Evaluating Evapotranspiration for Six Sites in Benton, Spokane, and 

Yakima Counties, Washington, May 1990 to September 1992

By Stewait A. Tomlinson

U.S. Geological Survey

Water-Resources Investigations Report 96-4002

Prepared in cooperation with

WASHINGTON STATE DEPARTMENT OF ECOLOGY

Tacoma, Washington 

1996
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

For additional information write to: Copies of this report may be

purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

1201 Pacific Avenue - Suite 600 Box 25286, MS 517

Tacoma, Washington 98402 Denver, Colorado 80225
CONTENTS

Abstract 1

Introduction 2

Background 2

Purpose and scope 2

Acknowledgments 7

Description of the study areas 7

Climate - - - - - - - - - - - 7

Vegetation 8

Soils and geology 9

Hydrology 10

Methods of estimating evapotranspiration - 11

Instrumentation 13

Energy-budget methods 13

Bowen-ratio method 17

Penman-Monteith method 17

Canopy resistance 17

Aerodynamic resistance 18

Weighing lysimeters 20

Deep-percolation model 21

Evaluation of evapotranspiration 21

Energy budgets 22

Evapotranspiration estimates 28

Grass and sage lysimeter sites 28

Snively Basin site 45

Turnbull meadow and marsh sites 61

Black Rock Valley site 61

Water budgets 73

Grass and sage lysimeter sites 73

Snively Basin site 75

Summary and conclusions 79

References cited 82

FIGURES

1. Maps showing location of evapotranspiration study sites in Washington: 3

la. Grass lysimeter, sage lysimeter, and Snively Basin sites 4

Ib. Turnbull meadow and marsh sites 5

Ic. Black Rock Valley site 6

2-4. Diagrams showing:

2. Methods of estimating evapotranspiration and periods of data collection at the study sites 12

3. Evapotranspiration instrumentation setup 14

4. Energy budget in the canopy layer 16 

5-7. Graphs showing energy budget from the Bowen-ratio method at the:

5. Snively Basin site, April 9-15, 1992 23

6. Snively Basin site, May 7-13, 1992 ---------------------------------------------------------- 24

7. Turnbull meadow site, July 10-16, 1991 25

8. Graph showing energy budget from the Penman-Monteith method at the Turnbull meadow

site, October 1-7, 1991 26

9. Graph showing energy budget from the Bowen-ratio method at the Black Rock Valley

site, July 22-28, 1992 27

in
FIGURES-CONTINUED

10-12. Graphs showing latent-heat flux from the:

10. Bo wen-ratio and Penman-Monteith methods at the Snively Basin site, May 7-13, 1992 29

11. Bowen-ratio and Penman-Monteith methods at the Turnbull meadow site, July 10-16, 1991 30

12. Bowen-ratio and Penman-Monteith methods at the Black Rock Valley site,

July 22-28, 1992 31

13-19. Graphs showing daily evapotranspiration:

13. From weighing lysimeters at the grass lysimeter sites, May 30, 1990, to September 30, 1991 42

14. From weighing lysimeters at the grass and sage lysimeter sites, October 1, 1991, to

September 30, 1992 43

15. At the grass lysimeter site and Snively Basin sites, May 30, 1990, to September 30, 1991 56

16. At the grass lysimeter site and Snively Basin site, October 1, 1991, to September 30, 1992 57

17. At the Snively Basin site from the Penman-Monteith method and deep-percolation

model, May 30, 1990, to September 30, 1991 ~~~~-~~~~~~~~~~~ -------------------------- 58

18. At the Snively Basin site from the Penman-Monteith method and deep-percolation

model, October 1, 1991, to September 30, 1992 59

19. At the Turnbull meadow and marsh sites, May 15, 1991, to September 30, 1992 - 68

20. Graph of wind speed at 3.0 meters above the canopy for the Black Rock Valley site,

July 26 to August 6, 1992 72

21-23. Graphs showing:

21. Cumulative precipitation and evapotranspiration from weighing lysimeters at the

grass and sage lysimeter sites, August 20, 1990, to September 30, 1992 74

22. Cumulative precipitation and evapotranspiration at the Snively Basin and grass

lysimeter sites, August 20, 1990, to September 30, 1992 76

23. Cumulative precipitation and evapotranspiration from the Penman-Monteith

method and deep-percolation model at the Snively Basin site, August 20, 1990, to

September 30, 1992 78

TABLES

1. Instrumentation used at evapotranspiration study sites 15

2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter

sites, May 1, 1990, to September 30, 1992 32

3. Daily and monthly precipitation and evapotranspiration at the grass lysimeter site,

April 2 to May 13, 1991, and at the sage lysimeter site, July 23-30, 1992 44

4. Daily and monthly precipitation and evapotranspiration and canopy resistance at the

Snively Basin site, May 31, 1990, to September 30, 1992 46

5. Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and

marsh sites, May 16, 1991, to September 30, 1992 62

6. Daily and monthly precipitation and evapotranspiration for Black Rock Valley site,

March 27 to September 30, 1992 69

IV
CONVERSION FACTORS AND VERTICAL DATUM

Multiply

Area

square meter (m2) 

square kilometer (km2)

Density 

kilogram per cubic meter (kg/m3)

Energy 

joule (J) 

Energy-flux density

watt per square meter (W/m2) 

Energy and mass

joule per gram (J/g)

Flow

cubic meter per second

Length

millimeter (mm) 

meter (m) 

kilometer (km)

Mass

gram (g) 

Power

watt (W)

Pressure

kilopascal (kPa)

Resistance

second per meter (s/m)

Specific-heat capacity 

joule per gram per kelvin ([J/g]/K)

Temperature 

degrees Celsius (°C) 

kelvin (K) 

Velocity

meter per second (m/s)

Volume

cubic meter (m3)

By

10.76 

0.3861

0.06243

9.478X10'4 

5.285xlO'3

0.4298

15,850

0.03937 

3.281 

0.6214

2.205x1 0'3 

3.4129

0.1450

0.3048

0.2388

1.8°C + 32 

1.8 K- 459.67

2.237

35.31

To obtain

square foot 

square mile

pound per cubic foot

British thermal unit

British thermal unit per square 

foot per minute

British thermal unit per pound

gallons per minute

inch 

foot 

mile

pound 

British thermal unit per hour

pound per square inch

second per foot

British thermal unit per pound per 

degrees Fahrenheit

degrees Fahrenheit 

degrees Fahrenheit

miles per hour

cubic foot

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-

a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada,

formerly called Sea Level Datum of 1929.
SYMBOLS AND EQUATIONS

Symbols used in text;

P Bowen ratio, unitless

C Specific heat of air, equal to 1.005 joules per gram per degree Celsius

C Specific heat of soil, in joules per kilogram per degree Celsius

C Specific heat of water, in joules per kilogram per degree Celsius

D Depth, in meters

d Zero plane displacement height (distance from surface to mean height of heat, vapor, or momentum 

	exchange), in meters

ET Rate of evapotranspiration, in millimeters per day

e Vapor pressure, in kilopascals

e Saturated vapor pressure, in kilopascals

e Ratio of molecular weight of water to air, equal to 0.622

FXl Soil-heat flux measurement 1, in watts per square meter

FX2 Soil-heat flux measurement 2, in watts per square meter

G Soil-heat flux, in watts per square meter

H Sensible-heat flux, in watts per square meter

h Canopy height, in meters

h Relative humidity, in percent

K, Height-dependent exchange coefficient (eddy diffusivity) for heat transport, in square meters per second

K Height-dependent exchange coefficient (eddy diffusivity) for water-vapor transport, in square meters

w

	per second

k von Karman's constant, equal to 0.4, unitless

L Latent-heat of vaporization of water, in joules per gram

LE Latent-heat flux, in watts per square meter

LE Potential latent-heat flux, in watts per square meter

P Atmospheric pressure, in kilopascals

p Air density, in grams per cubic meter

p, Soil bulk density, in kilograms per cubic meter

9t Gas constant for dry air, equal to 0.28704 joules per gram per kelvin

R Net radiation, in watts per square meter

n

r Canopy resistance, in seconds per meter

VI
SYMBOLS AND EQUATIONS-CONTINUED

Symbols used in text:

rh

2

r 

S 

s 

T

T

s

t 

u 

W

z 

z.

Aerodynamic resistance to heat flow, in seconds per meter

Square of the correlation coefficient, unitless

Flux going into storage as soil heat, in watts per square meter

Slope of the saturation vapor-pressure curve at air temperature, in kilopascals per degree Celsius

Air temperature, in degrees Celsius

Soil temperature, in degrees Celsius

Time, in seconds

Wind speed, in meters per second

Percentage of water content by weight, in kilograms of water per kilogram of soil

Measurement height, in meters

Heat-transfer roughness length, in meters

Momentum roughness length, in meters

Psychrometric constant, in kilopascals per degree Celsius

Equations used in study text:

Num- Name and source 

her or derivation Equation

1. Energy budget

(Brutsaert, 1982, p. 2)

2. Latent-heat of vaporization of water

(W.D. Nichols, U.S. Geological 

Survey, written commun., 1990)

R = LE + H+G 

n

_ 9t [6, 788.6 - 5.0016 (T + 273.15 ) ]

 " " " 

3. Latent-heat of vaporization of water 

(Reduction of eq. 2)

L = 2, 502.3 - 2.308 T

4. Soil-heat flux

(Campbell Scientific, Inc., 1991, 

sec. 4, p. 3)

FXl + FX2

Vll
SYMBOLS AND EQUATIONS-CONTINUED

Equations used in study textj

Num- Name and source

ber or derivation Equation

5. Soil-heat storage 5= - \D pb [Cs +(W Cw)]

(Campbell Scientific, Inc., 1991, 

sec. 4, p. 3)

H

6. Bowen ratio p = - =, LE 

(Bowen, 1926)

P C K, ~

p n d? 1. Bowen ratio p = - 

T v de 

(Rosenberg and others, 1983, p. 255) L e K ~

P C AT 

8. Bowen ratio P = p

(Tanner, 1988)

9. Psychrometric constant y =

L e 

(Rosenberg and others, 1983, p. 255)

10. Bowen ratio P = y -T- 

(Substitution of eq. 9 into eq. 8)

11. Sensible-heat flux H - p LE 

(Rearrangement of eq. 6)

R -G

12. Latent-heat flux LE = " 0

1 +p 

(Substitution of eq. 11 for H,

then rearrangement of eq. 1)

Vlll
SYMBOLS AND EQUATIONS-CONTINUED

Equations used in study text;

Num- Name and source 

her or derivation Equation

13a. Rate of evapotranspiration 

(Campbell, 1977, p. 141)

ET = 86.4 LE

13b. Latent-heat flux

(Rearrangement of equation 13a)

LE =

ET L

86.4

14. Vapor pressure

(Rearrangement of equation for 

h in Rosenberg and others, 1983, 

p.r!71)

e = 0.01 e h 

s r

15. Saturated vapor pressure

(Stull, 1988, p. 276; equation 

adjusted for °C)

16. Slope of the saturated 

vapor pressure curve

(Derivation of eq. 15 and 

conversion of T in K to °C)

s = 0.6112 17.67 17.67 T

243.5)

\exp 17.67 T 

T+ 243.5

17. Aerodynamic resistance 

to heat (neutral conditions)

(Campbell, 1977, p. 138)

In

rh =

In

k u

18. Penman equation (potential 

evapotranspiration)

(Monteith, 1965)

LE = 

P

Cp (es -e}/rh

IX
SYMBOLS AND EQUATIONS-CONTINUED

Equations used in study text:

Number

Name and source 

or derivation Equation

19. Penman-Monteith equation 

(Monteith, 1965)

LE =

 \R -G] + [p C (e -e}\/r, |_ n J |_K a P s \

s + y

20. Canopy resistance

(Rearrangement of eq. 19)

-1J.

y LE s(R -G)

v n '

p C (e -e) K a /? v j y -r,
Evaluating Evapotranspiration for Six Sites in Benton, Spokane, and 

Yakima Counties, Washington, May 1990 to September 1992

By Stewart A. Tomlinson

ABSTRACT

This report evaluates evapotranspiration for six sites 

in Benton, Spokane, and Yakima Counties, Washington. 

Three sites were located on the Arid Lands Ecology 

Reserve in Benton County: one at a full-canopy grassland 

in Snively Basin (Snively Basin site), one at a sparsecanopy grassland adjacent to two weighing lysimeters 

(grass lysimeter site), and one at a sagebrush grassland 

adjacent to two weighing lysimeters (sage lysimeter site). 

Two sites were located on the Turnbull National Wildlife 

Refuge in Spokane County: one at a full-canopy grassland 

in a meadow (Turnbull meadow site), the other a fullcanopy grassland near a marsh (Turnbull marsh site). The 

last site was located in a sagebrush grassland in the Black 

Rock Valley in Yakima County (Black Rock Valley site).

The periods of study at the six sites varied, ranging 

from 5 months at the Black Rock Valley site to more than 

2 years at the Snively Basin, grass lysimeter, and sage 

lysimeter sites. The periods of study were May 1990 to 

September 1992 for the Snively Basin, grass lysimeter, 

and sage lysimeter sites; May 1991 to September 1992 for 

the Turnbull meadow site; May 1991 to April 1992 for the 

Turnbull marsh site; and March to September 1992 for the 

Black Rock Valley site.

Evapotranspiration and energy-budget fluxes were 

estimated for the Snively Basin site, the Turnbull meadow 

site, and the Black Rock Valley site using the Bowen-ratio 

and Penman-Monteith methods. Daily evapotranspiration 

for the Snively Basin site was also estimated using a 

deep-percolation model for the Columbia Basin. The 

Bowen-ratio method and weighing lysimeters were used at 

the grass and sage lysimeter sites. The Penman-Monteith 

method was used at the Turnbull marsh site.

Daily evapotranspiration at the sites ranged from 

under 0.2 millimeter during very dry or cold periods to 

over 4 millimeters after heavy rainfall or during periods of

peak transpiration. At all sites, peak evapotranspiration 

occurred in spring, coinciding with plant growth, and the 

lowest evapotranspiration occurred in late summer and 

winter, coinciding with plant dormancy and extremely hot 

or cold temperatures.

Water budgets for the Snively Basin, grass lysimeter, 

and sage lysimeter sites were based on estimates of precipitation, evapotranspiration, and surface runoff. Surface 

runoff was estimated at zero for all sites. For the Snively 

Basin site, 1991 and 1992 water budgets using PenmanMonteith evapotranspiration estimates agreed within 

1 percent of the annual budgets computed using deeppercolation model estimates; daily estimates of evapotranspiration by the two methods varied considerably, 

however. For the Snively Basin site, 100 percent of the 

precipitation became ET in 1991, and in 1992, about 

91 percent of the precipitation became evapotranspiration. 

Water budgets based on weighing lysimeter data at the 

grass and sage lysimeter sites agreed within 1 percent of 

each other for 1991 and within 5 percent of each other for 

1992. For 1991, 100 percent of the precipitation became 

ET at both lysimeter sites. For 1992, 94 to 98 percent of 

the precipitation became ET at the grass lysimeter site 

while 98 to 99 percent of the precipitation became ET at 

the sage lysimeter site.

Though there were uncertainties in the methods used, 

recharge estimates for the Snively Basin and grass and 

sage lysimeter sites were of the same order of magnitude. 

The Penman-Monteith method (which incorporated 

Bowen-ratio measurements), deep-percolation model, and 

weighing lysimeters indicated that no recharge to subsurface systems (soil profile, unsaturated zone, and ground 

water) occurred in 1991 and that, in 1992, recharge to subsurface systems was probably less than 10 percent of the 

annual precipitation at the Snively Basin and grass and 

sage lysimeter sites.
INTRODUCTION

Most of the precipitation that falls on grass and sagebrush-covered lands in semiarid eastern Washington is 

returned to the atmosphere as evapotranspiration (ET). 

Evapotranspiration, the amount of water evaporated from 

soil and other surfaces plus the amount of water transpired 

by plants, thus plays an important part in the hydrologic 

cycle for eastern Washington. Combined with precipitation and surface-water discharge data, ET estimates are 

commonly used to estimate ground-water recharge (Gee 

and Kirkham, 1984; Gee and Hillel, 1988; Bauer and 

Vaccaro, 1990). Thus, ET estimates are important to 

resource managers.

Background

ET is one of the most difficult components of the 

hydrologic cycle to quantify because of the complexity of 

collecting accurate data needed for its computation. Many 

environmental factors contribute to ET, each of which 

requires accurate measurement of a number of atmospheric variables under varied conditions. Some of these 

factors are particularly difficult to measure in semiarid 

areas; for example, the extremes of temperature and relative humidity are occasionally beyond the data-collection 

capabilities of available instruments.

In order to better estimate ET in eastern Washington, 

an ET study was established in August 1989 by the 

U.S. Geological Survey and the State of Washington 

Department of Ecology. New ET studies were established 

in 1990 and 1991 through similar agreements between the 

two agencies. The objectives of these studies were to 

make long-term estimates of ET for several sites in eastern 

Washington and to investigate a method of estimating ET 

requiring only standard meteorological, or easily collected, data.

Purpose and Scope

This report primarily describes the third phase of a 

study on ET for rangelands in eastern Washington. The 

report also provides summaries and supplemental information for the results of the first two phases. This report 

presents results of ET research at four grassland sites and 

two sagebrush sites in eastern Washington. Two of the 

grass sites are on the Arid Lands Ecology (ALE) Reserve 

near Richland; the other two are on the Turnbull National 

Wildlife Refuge (NWR), near Cheney (fig. 1). The ALE

Reserve sites are in (1) a full-canopy (80-100 percent 

cover) grassland in Snively Basin (Snively Basin site), (2) 

a sparse-canopy (25-60 percent cover) grassland near the 

base of an alluvial fan adjacent to two weighing lysimeters 

(grass lysimeter site), and (3) a sparse-canopy sagebrush 

steppe adjacent to two weighing lysimeters (sage lysimeter site). The two Turnbull NWR sites are in (1) a 

meadow-steppe grassland (Turnbull meadow site) and (2) 

a marsh grassland (Turnbull marsh site). Another site is 

located in sagebrush steppe near the base of an alluvial fan 

in the Black Rock Valley near Moxee City, Wash. (Black 

Rock Valley site, fig. 1). This report evaluates ET data 

collected at these sites for various periods in 1990, 1991, 

and 1992. Also, the report compares methods used to estimate ET and discusses the water budgets estimated with 

them. Previous reports described the first phase, which 

focused on methods, instrumentation, and preliminary 

results for estimating ET from the Snively Basin site 

(Tomlinson, 1994) and the second phase, which provided 

more detailed results and discussed differences between 

the Bowen-ratio and Penman-Monteith methods for 1990 

and 1991 data (Tomlinson, 1995).

Estimates of ET were made with the Bowen-ratio 

method, the Penman-Monteith method, weighing lysimeters, and a deep-percolation model for the Columbia 

Plateau. For estimates of ET with the Bowen-ratio and 

Penman-Monteith methods, instruments collected net radiation, air and soil temperatures, soil-heat flux, and 

soil-water content data. The Bowen-ratio method also 

required vapor-pressure measurements. Wind speed and 

relative humidity were collected for the Penman-Monteith 

method. Scales measured lysimeter masses to estimate 

weighing-lysimeter ET and precipitation. The deep-percolation model required solar radiation, air temperature, and 

precipitation data.

The study sites in eastern Washington were chosen 

for a variety of reasons. The Snively Basin site and the 

Turnbull meadow and marsh sites generally provided suitable conditions for using energy-balance methods of 

estimating ET because of their uniform canopy height, 

flat-to-gently sloping aspect, and extensive cover in their 

respective areas. The grass and sage lysimeter sites were 

chosen because of their proximity to weighing lysimeters. 

The Black Rock Valley site was chosen because of its 

gently-sloping aspect, extensive sagebrush cover, and relatively remote location. The grass and sage lysimeter sites 

and the Black Rock Valley site represent typical vegetation across much of eastern Washington.
Conversion for

topographic map

in Figures 1a, 1b, and 1c

118°

FEET

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

3400

METERS

=

=

=

=

=

=

=

=

=

=

=

366

427

488

549

610

671

732

792

853

914

975

1,036

'.U.S. DEPARTMENT OF ENERGY 

HANFORD SITE

YAKIMA FIRING

CENTER Umtanum 

Yakima ^, Moxee City I I Ridge

Figure 1c

BLACK ROCK 

VALLEY

Figure 1. Location of evapotranspiration study sites in Washington.
119°43'30 119°38' 46°28'

27' - 26'

46°25'30"

42' 40'

jCr «i=S^JL ii. i--_J -1. vf^" T- ' ^/fr"V- -i P-l,-^- " &*"! t I" Af^J -^ iS^k'-i-^- iJ^il__ / 

 -&%.-L , '- ' ^r ^Vx;^-:1 --^ -^

s o ~ i' o' - - -'"& ~e,", " '-.....- -:^f "' :~ ''-i^^^^*^-''-^:-

ff^M,* (I - «'-%. ' i i AX~y '! /'! J.i, ... , J. >.( ;/ v ,,ir, i '. £ > t : - - .^iM^.^,% ' $..

Base from U.S. Geological Survey Snively Basin, 1974,1:24000 R.25 E.

CONTOUR INTERVAL 40 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 1a.--Location of grass lysimeter, sage lysimeter, and Snively Basin sites.
117°35' 34' 117°30'

47°26'30

47°24 R.41 E. R.42 E.

Base from U.S. Geological Survey Cheney, 1980,1:24 000

CONTOUR INTERVAL 10 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 1b.--Location of Turnbull meadow and Turnbull marsh sites.
120°12' 120°08'

46°35'

46°33'

Base from U.S. Geological Survey Black Rock Springs SW, 1953,1:24 000 R.21 E

CONTOUR INTERVAL 20 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 1c. Location of Black Rock Valley site.
Acknowledgments

The author thanks Battelle, Pacific Northwest 

Laboratories for their assistance in obtaining permission to 

install ET instrumentation on the ALE Reserve and for 

providing the U.S. Geological Survey with data from 

weighing lysimeters on the ALE Reserve. The author also 

thanks the U.S. Fish and Wildlife Service for their assistance in obtaining required permits and in site selection for 

instrumentation on the Turnbull NWR. The author thanks 

Mr. Simon Martinez and his family for their cooperation 

and permission to install ET instruments on their property 

in the Black Rock Valley. Also, thanks are given to the 

U.S. Army, Department of Defense, for their permission to 

access the Black Rock Valley site using roads on the 

Yakima Training Center.

DESCRIPITON OF THE STUDY AREAS

All study sites are located in eastern Washington (see 

fig. 1). The Snively Basin site, grass lysimeter site, and 

sage lysimeter site are located in the Rattlesnake Hills on 

the ALE Reserve of the Hanford Site (also called Hanford 

Works, Hanford Reservation, or simply Hanford in many 

publications, maps, and documents) in western Benton 

County, Washington, about 64 kilometers (km) east of 

Yakima and 40 km west of Richland (fig. la). The ALE 

Reserve encompasses diverse topography with altitudes 

ranging from 134 meters (m) in the lower valleys to 

1,073 m at the crest of the Rattlesnake Hills. Dominant 

physical features of the surrounding area are the Columbia 

River to the north and east, the Yakima River to the south, 

and the Cascade Range about 160 km to the west. The 

Snively Basin site is at an altitude of 494 m. About 450 m 

apart, the grass and sage lysimeter sites, adjacent to four 

weighing lysimeters (two at each site), occupy an alluvial 

fan 5 km northeast of the Snively Basin site, at an altitude 

of 293m.

The Turnbull meadow and marsh sites are located on 

the Turnbull NWR about 7 km southeast of Cheney, Wash, 

(fig. Ib). The Turnbull NWR topography is flat to gently 

sloping and dotted by many permanent and seasonal lakes 

and ponds. Major physiographic features of the surrounding area are the Palouse Hills, about 10 km south and west, 

and the Spokane River, about 50 km north. The Turnbull 

meadow site is located in a grass meadow at an altitude of 

706 m. The Turnbull marsh site is located on a grass knoll 

at an altitude of 696 m in a marshy area of seasonal wetlands.

The Black Rock Valley site (fig. Ic) lies at an altitude 

of 762 m in an area locally called The Big Flat between 

the Yakima Ridge, about 2.5 km to the north, and a small, 

unnamed ridge about 1.3 km to the south. The site is 

located about 14 km east northeast of Moxee City, Wash. 

Altitudes in the area range from 1,278 m at the crest of the 

Yakima Ridge to 700 m at the lowest part of the unnamed 

valley. Major nearby physiographic features are the 

Umptanum Ridge, 10 km north of the site, the Yakima 

River, 20 km west of the site, and the Cascade Range, 

120 km west of the site.

Climate

The semiarid climate of eastern Washington results 

primarily from the rain-shadow effect of the Cascade 

Range. The Cascade crest varies between 1,200 and 

3,050 m above sea level and forms an effective barrier to 

storms moving in from the Pacific Ocean. West of the 

Cascades, Olympia receives about 1,270 mm of precipitation annually, whereas east of the Cascades, Yakima 

receives only about 203 millimeters (mm) a year (Ruffner 

and Bair, 1987). From Yakima, annual precipitation gradually increases to the east with Walla Walla receiving 

about 383 mm and Spokane getting about 411 mm 

(Ruffner and Bair, 1987). Precipitation on the ALE 

Reserve from 1969 through 1980 ranged from about 

165 mm/yr in the lower altitudes to over 280 mm annually 

just north of the Rattlesnake Hills crest (Stone and others, 

1983). The Snively Basin site is located in one of the wettest areas of the ALE Reserve. Based on an average of 

three precipitation stations close to the Snively Basin site 

(Stone and others, 1983), the estimated annual precipitation at the site averages 245 mm. For the grass and sage 

lysimeter sites, estimated annual precipitation averages 

about 209 mm on the basis of an average of two nearby 

stations reported by Stone and others (1983). More than 

75 percent of the annual precipitation on the ALE Reserve 

falls from October to April, about one-fourth of it as snow. 

June to September is normally the driest time of year, 

though convective storms during this period can account 

for as much as 20 percent of the annual precipitation 

(Stone and others, 1983).

Average annual precipitation at Turnbull NWR has 

not been determined, but is likely to be similar to that 

at Cheney, only 7 km away. Annual precipitation at 

Cheney was measured from 1938-55 and averaged 

491 mm (Maytin and Gilkerson, 1962). Annual precipitation at other nearby stations averages 373 mm at Sprague 

(Maytin and Gilkerson, 1962), 30 km west, and 411 mm at 

Spokane (Ruffner and Bair, 1987), 48 km northeast. As at
the ALE Reserve sites, more than 75 percent of the total 

annual precipitation falls from October to April, with 

one-fourth to one-third in the form of snow (Ruffner and 

Bair, 1987). July to September is usually the driest part of 

the year. Thunderstorms form most often from May to 

September and can provide as much as 10 percent of the 

annual precipitation.

Because of the remoteness of the Black Rock Valley 

site, precipitation has not been documented there. The 

site's altitude of 762 m suggests that its average annual 

precipitation should be slightly greater than that at Moxee 

City (472 m), which averages 208 mm annually (Maytin 

and Starr, 1960). Precipitation patterns in the Black Rock 

Valley are probably similar to those on the ALE Reserve, 

40 km to the southeast.

Dew adds to precipitation at all sites. Monteith 

(1963a) estimated that precipitation as dewfall can range 

from 10 to 40 mm annually in some climates. No measurements of dew have been made on the ALE Reserve, 

Black Rock Valley, or Turnbull NWR. However, Rickard 

and others (1988) estimate dew at less than 5 percent of 

the annual precipitation on the ALE Reserve on the basis 

of available meteorological data.

Temperature patterns at all sites are primarily continental (influenced more by air masses moving over land 

rather than over water), but frequent storms move in from 

the Pacific Ocean, mainly during the winter months, moderating temperatures and bringing precipitation. For the 

weather station nearest to the ALE Reserve, located at 

Hanford (meteorological station), about 21 km from the 

Snively Basin site, annual temperatures average 

11.7 degrees Celsius ( C). Temperature extremes at 

Hanford range from 46 to -33 C (Stone and others, 1983). 

At Moxee City, 14 km from the Black Rock Valley site, 

the average annual temperature is 9.1 C, and extremes 

range from 39 to -29°C (Maytin and Starr, 1960). At 

Cheney, 7 km from the Turnbull NWR sites, the average 

annual temperature is 8.7 C and temperature extremes 

range from 42 to -37 C (Maytin and Gilkerson, 1962).

Vegetation

The study sites are located in grasslands or sagebrush 

steppes. The Snively Basin and grass lysimeter sites on 

the ALE Reserve are covered by cheatgrass (Bromus 

tectorum), bluebunch wheatgrass (Agmpyron spicatum), 

and Sandberg's bluegrass (Poa sandbergii). At the sage 

lysimeter site, big sagebrush (Artemesia tridentatd) grows 

with these grasses. Cheatgrass, an invasive grass from

Europe introduced to Washington about 1890 (Franklin 

and Dyrness, 1988), predominates at the Snively Basin 

site. Bluebunch wheatgrass and Sandberg's bluegrass predominate at the grass lysimeter site. Big sagebrush, bluebunch wheatgrass, and Sandberg's bluegrass predominate 

at the sage lysimeter site. Vegetation covers 80 to 

100 percent of the surface at the Snively Basin site and 25 

to 60 percent at the grass and sage lysimeter sites. The 

height of the grassland canopy was about 0.35 m at the 

Snively Basin site and 0.25 m at the grass lysimeter site. 

At the sage lysimeter site, the average height of the sagebrush was 1.0 m and of the grasses 0.25 m. At the Snively 

Basin site, roots from the grasses generally extended into 

the soil about 0.20 m, although some roots were found as 

deep as 1.1 m. Franklin and Dyrness (1988) found cheatgrass roots as deep as 0.97 m. Sagebrush has a taproot that 

can penetrate 1 to 4 m, but a caliche layer at 2 m at the 

sage lysimeter site probably limits rooting to that depth.

Other plants occurring in small numbers among the 

grasses and sagebrush on the ALE Reserve include rabbitbrush (Chrysothamnus nauseouses), bitterbrush (Purshia 

tridentatd), Carey's balsamroot (Balsamorhiza careyana), 

showy phlox (Phlox speciosd), and lupine (Lupinus sp.\ 

Sagebrush is probably the climax (stable stage of plant 

succession) species on the ALE Reserve, but it is firesensitive (Franklin and Dyrness, 1988). A major fire 

in 1984, which burned 80 percent of the ALE Reserve 

(Rickard and others, 1988), eliminated sagebrush at the 

Snively Basin and grass lysimeter sites. Grasses cover the 

surface in all directions for distances of 400 m to 3 km and 

further at the Snively Basin and grass lysimeter sites. The 

sage lysimeter site is located at the northeastern edge of a 

large area of sagebrush. Grasses begin about 30 to 100 m 

north and east of the sage lysimeter site, probably corresponding with the edge of the 1984 burn. Sagebrush 

extends over 1 km to the west and south of the sage lysimeter site.

Small areas of riparian vegetation grow near springs 

on the ALE Reserve. Areas such as Snively Gulch have 

small numbers of woody plants, including trees. Plant 

identification was aided by Hayes and Garrison's "Key 

to Important Woody Plants of Eastern Oregon and 

Washington" (Hayes and Garrison, 1960). Included 

among these trees are Black cottonwood (Populus trichocarpd), Common chokecherry (Prunus virginiana), 

Columbia hawthorne (Crataegus columbiana), several 

species of willow (Salix sp.), and a naturalized exotic, 

White poplar (Populus alba). At the weighing lysimeter 

sites, the closest trees are several naturalized Siberian elms 

(Ulmuspumila) at an abandoned ranch about 3.2 km away.
At the ALE Reserve sites, vegetation grows most rapidly during the wet winter and spring seasons. Growth 

peaks from March to May, when ET is also at its maximum because of the transpiration from the growing vegetation. Dryer summer weather beginning in June slows 

growth and ultimately causes the grasses to seed and perish or go dormant. At this time, sagebrush begins to lose a 

number of leaves in response to the drying conditions. In 

late summer and early fall, usually the driest time of year, 

sagebrush blooms while grasses are completely dormant. 

Grasses begin growing again in fall when the first major 

precipitation occurs.

The Turnbull meadow site is located in an area of 

meadow steppe dominated by perennial grasses. Predominant species are Idaho fescue (Festuca idahoensis), 

bluebunch wheatgrass (Agropyron spicatum), Men-ill's 

bluegrass (Poa ampld), Sandberg's bluegrass (Poa 

sandbergii), and Kentucky bluegrass (Poa pratensis). 

Mixed with the grasses are an abundance of other annual 

and perennial plants such as silky lupine (Lupinus 

sericeus), western yarrow (Achillea millefolium), and 

sticky geranium (Geranium viscosissimum). Vegetative 

cover is very thick and lush and the canopy height averages 0.91 m. The grasses extend at least 600 m in all directions from the Turnbull meadow site. Beyond that 

distance to the west and north, small patches of Ponderosa 

pine (Pinus ponderosa) mix with the grasses.

The Turnbull marsh site is located in a mixed grass 

community on a peninsular knoll bordered by a seasonal 

wetland on three sides. The knoll rises about 3 m above 

the bed of the seasonal wetland and is about 4.5 m wide 

and 9 m long. The vegetation includes a mixture of 

grasses including wheatgrass (Agropyron species) and 

ryegrass (Lolium species). Other vegetation includes bulrushes (Scirpus species), sedges (Carex species), common 

rush (Juncus effuses), common cat-tail (Typha latifolia), 

and common thistle (Cirsium vulgare). Vegetation is 

dense and averages 0.61 m high. The mixed grasses 

extend over 500 m to the north, east, and west and about 

300 m to the south.

A variety of trees and shrubs also grow on the 

Turnbull NWR. Thickets of round-leaved snowberry 

(Symphoricarpos albus) grow near the Turnbull meadow 

and marsh sites. The predominant tree in the dryer areas 

is Ponderosa pine (Pinus ponderosa). Creeks in the 

area support other trees such as quaking aspen (Populus 

tremuloides) and common chokecherry (Prunus 

virginiana). A great variety of other plant life grows on 

the Turnbull NWR (U.S. Fish and Wildlife Service, 1991).

Most vegetation at the Turnbull NWR sites remain 

dormant during the winter. The grasses begin growth at 

the Turnbull meadow site in March, with maximum 

growth from May through mid-July. Dry summer weather 

from mid-July through September slowly causes the vegetation to seed and perish or go dormant. At the Turnbull 

marsh site, plant growth also begins in March; however, 

the water table remains high enough for most vegetation to 

remain active into September. Freezing temperatures usually begin in September or October causing vegetation 

remaining in growth to go dormant or perish.

At the Black Rock Valley site, bluebunch wheatgrass, 

Sandberg's bluegrass, and big sagebrush predominate. 

Stiff sagebrush (Artemesia rigidd) and desert buckwheat 

(Eriogonum thymoides) also grow in areas surrounding the 

site. Relatively few other plants grow near the site there 

is a noticeable absence of annuals and non-grass perennials. The grasses average 0.4 m in height and the sagebrush 

0.9 m in height. Sagebrush-covered areas extend over

3 km to the west, north, and east of the site. Towards the 

south and southwest, sagebrush extends about 400 m, 

where an abandoned field covers areas further away. The 

plant growth cycle is similar to that of the ALE Reserve 

sites, with the exception that growth begins about 2 to

4 weeks later in spring because of colder temperatures 

resulting from the higher elevation of the Black Rock 

Valley site. ET is also higher in late summer and early fall 

at the Black Rock Valley site, compared with the ALE 

Reserve sites.

Soils and Geology

All study sites are located in the Columbia Plateau 

physiographic province. The major surficial rock features 

of this area are numerous layers of basalt, the result of lava 

flows during the Miocene and Pliocene epochs, with thin 

sedimentary and volcanic ash interbeds. Silt, gravel, and 

other alluvial deposits left as a result of the so-called 

Spokane Flood (actually a series of floods) that swept 

across the Columbia Plateau during the Pleistocene epoch 

(Alt and Hyndman, 1984) cover much of the lower elevations of the Columbia Plateau. Windblown loess was 

deposited over much of the Plateau during the Pleistocene 

and Holocene epochs.

The ALE Reserve is on the north side of the 

Rattlesnake Hills within the Pasco Basin. Loess, 

fine-grained sand, and layers of volcanic ash cover the 

ALE Reserve (Rockwell International, 1979). Bedrock 

consists of basalt.
The predominant soil at the Snively Basin site, 

Ritzville silt loam, is a dark grayish-brown silt-loam soil 

that develops under grassland from silty wind-laid deposits mixed with small amounts of volcanic ash (Hajek, 

1966). Ritzville silt loam is generally greater than 1.5 m 

thick and has high water-holding capacity, moderate 

permeability, and low runoff potential (U.S. Department 

of Agriculture, 1971).

Warden silt loam predominates at the grass and sage 

lysimeter sites. Permeability, water-holding capacity, and 

runoff potential of Warden silt loam are similar to those of 

Ritzville silt loam. This soil differs from the Ritzville silt 

loam in that it becomes strongly calcareous about 0.5 m 

below the surface. Granitic boulders are found in many 

areas with Warden silt loam soil. These boulders were 

carried to the area with glacial ice by the Spokane Flood. 

Hajek (1966) reports that Warden soils intergrade to 

Ritzville soils at an altitude of approximately 366 m.

The Turnbull NWR is located along the eastern margin of the Columbia Plateau in an area called the channeled scablands (Olson and others, 1975). This area was 

one of the major watercourses of the Spokane Flood (Alt 

and Hyndman, 1984), and heavy scouring of the basalt 

bedrock by the Spokane Flood created many various-sized 

basins that are the present-day coulees, potholes, ponds, 

and lakes in the area. The predominant orientation of 

these features is southwest to northeast, parallel with the 

main flow direction of the Spokane Rood. Bedrock is 

basalt.

The Turnbull meadow site is covered by Hesseltine 

silt loam. This soil developed from gravelly outwash 

materials with a thin mantle of loess (Maytin and 

Gilkerson, 1962). Hesseltine silt loam covers nearly level 

to gently sloping areas, and basalt bedrock is usually about 

0.3 m below the surface.

The Turnbull marsh site is located on a peninsular 

knoll that was constructed in the 1960's, and the soil making up the knoll is probably a mixture of several soil types. 

From samples taken of the top 0.2 m of the soil profile, 

Saltese muck appears to be the predominant soil type. The 

Saltese muck typically forms in areas having a high water 

table (Maytin and Gilkerson, 1962). The first 0.5 m of 

depth is composed of a black, granular, permeable muck. 

Underneath are reddish-brown layers of raw peat derived 

from tules, reeds, and sedges.

Willis silt loam lies at the Black Rock Valley site. It is 

a moderately deep, well-drained soil formed from loess 

(U.S. Department of Agriculture, 1985). Permeability of

the Willis silt loam is low to moderate, water-holding 

capacity is high, and runoff potential is moderate (U.S. 

Department of Agriculture, 1985). A hardpan exits in the 

soil at a depth of 0.5 to 1.0 m, and bedrock is basalt.

Hydrology

At all study sites, most precipitation is lost to ET. For 

the sites on the ALE Reserve, there is probably little 

ground-water recharge except during very wet periods in 

some winters, when ET is minimal. In a water-balance 

study for a sandy soil at the Hanford Site, Gee and 

Kirkham (1984) reported that 5 cm of water penetrated 

3.5 m below the land surface in wet years. Link and others 

(1990) found that grass-covered areas of the ALE Reserve 

held more water at depths of 2.75 m than areas covered 

with sagebrush. Consequently, grass-covered areas, such 

as the Snively Basin and grass lysimeter sites, would be 

expected to allow more recharge than areas covered with 

the deeper-rooted sagebrush, which would remove deeper 

soil moisture.

Schwab and others (1979) described 125 springs on 

the ALE Reserve and found flows ranging from small 

seeps with instantaneous discharges estimated at less than 

1.6 x 10'5 m3/s (one-quarter gallon per minute) to streams 

originating from multiple springs with combined flows of 

4.4 x 10~3 m3/s (70 gallons per minute). Streams composed of discharge from these springs and seasonal snowmelt from higher elevations flow down to the lower 

elevations of the ALE Reserve, where they disappear 

along losing reaches. In so doing, these streams reportedly recharge a perched water table, which is about 30 m 

above the regional static water table (Harr and Price, 

1972).

The largest spring in Snively Basin is Lower Snively 

Spring, with an estimated flow of about 2.8 x 10~3 m3/s 

(45 gallons per minute) (Schwab and others, 1979). The 

gaining reaches of the Snively Spring system represent the 

primary surface runoff in Snively Basin except during and 

shortly after intense rainfall.

The closest spring to the grass and sage lysimeter sites 

is Benson Spring. It is located 2 km south of the sites and 

flows at an estimated 6.2 x 10 m3/s (10 gallons per minute) 

(Schwab and others, 1979).

At the Turnbull NWR, some ground-water recharge 

probably occurs during most years, though timing and 

amounts are variable. In a study of southern Spokane 

County, Olson and others (1975) estimated that about 2 to

10
3 percent of the annual precipitation reached aquifers. 

Recharge occurs mainly through infiltration along stream 

channels and from wetlands in the area. Lakes and basins 

in the area refill through a combination of ground-water 

discharge and overland runoff.

From November through February at the Turnbull 

NWR, ET rates are very low (because of the cold 

weather), while precipitation is at its highest for the year. 

Under these conditions, seasonal basins and lakes are 

refilled, and marshes and other wetlands are reflooded. 

The basin and lakes refill primarily as a result of 

ground-water discharge (JJ. Vaccaro, U.S. Geological 

Survey, oral commun., 1995) as water tables rise due to 

precipitation that infiltrates subsurface systems (soil moisture and ground water). Some precipitation may become 

overland runoff and contribute to refilling the basins, 

lakes, and marshes during heavy rain or from rain falling 

on frozen ground. Part of the recharged soil moisture is 

significantly lost to ET from about March to July. By 

August or September, the lakes and wetlands have much 

lower water levels or, in some cases, have become dry. 

The amount of water-level decline is variable from year to 

year, depending on precipitation, air temperature, solar 

radiation and other meteorological factors. Autumn rains 

usually start in October, beginning the cycle again.

At the Black Rock Valley site, there are several seeps 

west and east of the site that flow southward from the 

Yakima Ridge through canyons to the main part of the 

Black Rock Valley. One of these canyons is about 2.5 km 

west of the site. Another canyon lies 4 km east of the site. 

Normally the drainages in these two canyons are dry in the 

upper reaches, but water may run in them during and 

shortly after intense rainfalls. No measurements of these 

drainages are available. Depth to the water table is not 

known at the Black Rock Valley site, but it must be fairly 

close to the surface in an area about 5 km southeast of the 

site, where several small cottonwood and willow trees are 

growing. In a field about 1 km west of the Black Rock 

Valley site, however, water was first reported at about 

150 to 200 m below the surface while drilling a well 

(S. Martinez, oral commun., 1994).

METHODS OF ESTIMATING 

EVAPOTRANSPIRATION

Several methods of data collection and analysis were 

used in this study to estimate ET; instruments, energybudgets, weighing lysimeters, and the Columbia Plateau 

deep-percolation model (model). Instruments measured 

solar radiation, net radiation, wind speed, air temperature, 

vapor pressure, relative humidity, soil temperature, soilheat flux, and precipitation. Field personnel collected soil 

samples during site visits; laboratory analysis of these 

samples determined soil-water content. Net radiation, air 

temperature at two heights, vapor pressure at two heights, 

soil temperature, soil-heat flux, and soil-water content 

were required to estimate ET with the Bowen-ratio 

method. Net radiation, wind speed, air temperature, 

relative humidity, soil temperature, soil-heat flux, and 

soil-water content were required to estimate ET with the 

Penman-Monteith method. Precipitation and solar radiation data were not required for the Bowen-ratio or 

Penman-Monteith methods; those data assisted in interpreting the other data such as relative humidity and 

soil-heat flux and were also used in the model. ET was 

calculated from the weighing lysimeters by determining 

daily weight differences in the lysimeters. Model ET estimates required solar radiation, air temperature, and precipitation data.

ET was estimated for different periods with a 

different combination of methods at each site (fig. 2). 

For the Snively Basin site, instruments collected data from 

May 30, 1990 to September 30, 1992, and ET was estimated with the Bowen-ratio and Penman-Monteith methods. Also, the model was used to estimate ET at the 

Snively Basin site for August 20, 1990 to September 30, 

1992. At the grass and sage lysimeter sites, weighing 

lysimeters collected data from May 1, 1990 to 

September 30, 1992. In addition, Bowen-ratio data were 

collected from April 1 to May 14, 1991 at the grass lysimeter site and from April 30 to September 30, 1992 at the 

sage lysimeter site. For the Turnbull meadow site, instruments collected data from May 15, 1991 to September 29, 

1992, and ET was estimated with the Bowen-ratio and 

Penman-Monteith methods. For the Turnbull marsh site, 

instruments collected data from May 15, 1991 to April 29, 

1992, and ET was estimated with the Penman-Monteith 

method. For the Black Rock Valley site, instruments collected data from March 26 to September 30,1992, and ET 

was estimated with the Bowen-ratio and PenmanMonteith methods.

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Instrumentation

Figure 3 shows the instruments used to collect data 

needed to estimate ET at the six sites. Table 1 describes 

each of the instruments. More detailed information on the 

instruments is presented by Tomlinson (1994) in the first 

phase report for this study. Two sets of instruments collected data at the Snively Basin site, the Turnbull meadow 

site, and Black Rock Valley site (fig. 3). One set of instruments collected data primarily for the Bowen-ratio 

method, and the other set of instruments primarily gathered data for the Penman-Monteith method. Only 

Bowen-ratio instruments collected data at the grass and 

sage lysimeter sites. At the Turnbull marsh site, only 

Penman-Monteith instruments collected data. The 

Bowen-ratio set of instruments included one data logger, 

one net radiometer, one set of four averaging soil-temperature thermocouples, two soil-heat-flux transducers, one 

cooled-mirror hygrometer with two air intakes, and two 

air-temperature thermocouples. The Penman-Monteith set 

of instruments included one data logger, one net radiometer, one pyranometer, one anemometer, one air temperature and relative-humidity probe, one precipitation gage, 

one set of four averaging soil-temperature thermocouples, 

and two soil-heat-flux transducers. Additionally, personnel collected soil samples during visits at all sites in order 

to estimate the soil-water content which was used to estimate the soil-heat storage term for the Bowen-ratio and 

Penman-Monteith methods.

Each set of instruments was mounted on a separate 

tripod and mast. Soil-heat-flux transducers and averaging 

soil-temperature probes were installed below the soil surface. To estimate the soil-heat storage term for both methods, soil samples collected from all sites were analyzed for 

water content.

Several problems with the instrumentation resulted in 

incomplete or erroneous data. Burrowing animals damaged the soil-heat-flux transducer wires at the Snively 

Basin, Turnbull meadow, Black Rock Valley, and sage 

lysimeter sites on several occasions during the period of 

study. At the Snively Basin site, the motor driving the 

pump for the cooled-mirror hygrometer ran intermittently 

between June 25 and July 10, 1990; the pump was 

replaced July 11, 1990. At the Snively Basin site on 

August 21, 1990, rain or hail from a thunderstorm broke 

the lower fine-wire thermocouple, which was replaced 

September 6, 1990. Ice formed on the mirror of the 

cooled-mirror hygrometer on several occasions at the 

Snively Basin site in October 1990 and September 1991; 

at the Turnbull meadow site in July and September 1991; 

at the sage lysimeter site in May, June, July, and

September 1992; and at the Black Rock Valley site in May 

and June 1992. An animal chewed through the battery 

cable at the sage lysimeter site on July 31, 1992; this was 

repaired on August 14,1992. Other inexplicable problems 

occurred with the cooled-mirror hygrometer at the sage 

lysimeter site that resulted in invalid vapor-pressure data 

for most of the May to September 1992 data-collection 

period. The cooled-mirror hygrometer at the sage lysimeter site was subsequently sent to the manufacturer for 

repair, where problems with the cooled mirror were corrected. When instrument problems occurred intermittently, erroneous data values were replaced with estimates 

made by averaging valid values on each side of the erroneous one. Differences between like instruments probably 

produced little error in the resultant ET estimates. In 

a study conducted from September 5-13, 1991 at the 

Snively Basin site, like instruments were compared 

(Tomlinson, 1995). Net radiometers differed by 4 percent, 

soil-heat-flux transducers by 28 percent, air temperature 

by 4 percent, and vapor-pressure by 10 percent (2 days 

only). The study determined that if all instruments varied 

by the maximum amount, only a 12 percent change in ET 

would result from the Bowen-ratio method. More likely, it 

is less than 12 percent because some errors would probably mitigate others.

Energy-Budget Methods

Energy-budget methods employed in the study use the 

equations, terms, and symbols at the beginning of the 

report. Detailed information on the equations for this specific study are presented by Tomlinson (1994). Additionally, the Bowen-ratio and Penman-Monteith methods are 

described in great detail in textbooks written by Campbell 

(1977), Brutsaert (1982), Rosenberg and others (1983), 

and Monteith and Unsworth (1990). The notation and 

form of the equations in these texts may differ from this 

report, but the principles are the same.

ET involves a phase change of water from liquid to 

vapor (a process requiring energy) and the movement of 

that vapor into the atmosphere. It can be conceptualized 

as taking place as part of an energy budget, which has four 

main flux components; net radiation, latent-heat flux, sensible-heat flux, and soil-heat flux. Field measurements of 

the energy-budget components encompass a layer with its 

upper boundary just above the plant canopy and its lower 

boundary just below the soil surface (fig. 4); in this report, 

this layer is called the canopy layer. In the energy budget 

equation (eq. 1, located at the beginning of the report), net 

radiation equals the sum of the other three fluxes.

13
1.

2.

3.

4.5.6.7.

EXPLANATION

Net radiometer 8.

Pyranometer 9.

Anemometer 10. 

Temperature relative-humidity probe

Precipitation gage 11.Enclosure with data logger 12.Battery 13.

Soil-temperature thermocouples 

Soil-heat-flux transducers 

Enclosure with data logger and 

cooled-mirror hygrometer 

Air intake for hygrometer 

Fine-wire thermocouple 

Solar panel

PENMAN-MONTEITH 

INSTRUMENTATION

BOWEN-RATIO 

INSTRUMENTATION

Figure 3.--lnstrumentation setup at the evapotranspiration sites.
Table I.. Instrumentation used at evapotranspiration study sites

Instrument type Function Manufa

Data logger Scan instruments, record and process data Campbell Scientific 

Net radiometer Measure net radiation Radiation and Ener

Pyranometer Measure solar and diffuse radiation LI-COR (LI-200S)

Anemometer Measure wind speed Met One (014A)

Temperature-relative humidity probe Measure air temperature and relative humidity Campbell Scientific 

Precipitation gage Measure precipitation Texas Electronics (

Soil-temperature thermocouple Measure average soil temperature Radiation and Ener

Soil-heat flux transducer Measure soil-heat flux Radiation and Ener

Cooled-mirror hygrometer Measure vapor pressure and dew point General Eastern (D

Fine-wire thermocouple Measure air temperature Campbell Scientific 
Net 

radiation

Sensibleheat 

flux

Latentheat 

flux

i Canopy 

/ layer

Figure 4.--Energy budget in the canopy layer.

Defined as the sum of all incoming shortwave solar 

radiation and incoming longwave sky radiation minus the 

sum of reflected solar radiation and emitted longwave 

radiation (Haan and others, 1982), net radiation, R , provides the major energy source for the energy budget. Net 

radiation is considered positive when the sum of incoming 

radiation fluxes exceeds the sum of outgoing radiation 

fluxes.

Latent-heat flux, LE , results from the vaporization 

and movement of water. It is the product of the latent heat 

of vaporization of water and ET (eq. 13b). In this report, 

latent-heat flux is considered positive when vapor is transferred upward across the canopy layer.

Sensible-heat flux, H , is a turbulent, temperaturedriven heat flux resulting from differences in temperature 

between soil and vegetative surfaces and the atmosphere. 

In this report, sensible-heat flux is considered positive 

when heat is transferred upward from the surface across 

the upper boundary of the canopy layer. During the daytime, positive sensible-heat flux is often the result of surface heating. At night, sensible-heat flux is often less than 

zero, the result of surface cooling.

Soil-heat flux, G, represents energy moving downward through the soil from the land surface (eq. 4). Temperature gradients in the soil are measured by soil-heat 

flux transducers. The transducers measure the gradient 

across a material of known thermal conductivity. The 

thermal conductivity of the soil changes with soil-moisture content and is probably different from the transducer 

material these differences produce small changes in the 

overall soil-heat flux and are ignored in this study. 

Soil-heat flux includes the amount of energy that is stored 

in or comes from the layer of soil between the surface and 

the point of measurement (eq. 5). In this report, soil- heat 

flux is considered positive when moving downward 

through the soil from the land surface and negative when 

moving upward through the soil towards the surface.

One of the requirements for use of energy-budget 

methods is that the wind must move over a sufficient distance of like vegetation and terrain before it reaches the 

sensors. This distance is termed fetch, and the fetch 

requirement is generally considered to be 100 times the 

height of the sensors (Campbell, 1977, p. 40). At the 

study sites, the maximum sensor height above the canopy 

was 3.0 m. Therefore, a minimum of 300 m of similar

16
vegetation and terrain should be present at the sites. This 

requirement was met in all directions at all of the study 

sites except for one direction at the sage lysimeter site and 

possibly one direction at the Black Rock Valley site. The 

sage lysimeter site is at the northern end of an extensive 

patch of sagebrush but only about 30 to 100 m from an 

area with grasses but no sagebrush. Winds coming 

directly from the south passed over this grassy area before 

reaching the instruments at the sage lysimeter site, so there 

may have been times during the study period when fetch 

requirements were not met. To compare Bowen-ratio ET 

estimates with weighing- lysimeter ET, it was necessary to 

set the Bowen-ratio instruments in this part of the sagebrush patch so they could collect data adjacent to the 

weighing lysimeters. Whether the differences between the 

non-sagebrush area and the sagebrush area were sufficient 

to affect the data that were collected is not known because 

most of the vapor-pressure data collected at the site was 

erroneous because of sensor malfunctions. From weighing-lysimeter ET results at the grass and sage lysimeters 

sites, however, ET appeared to be nearly the same in sage 

and non-sage areas. At the Black Rock Valley site, the 

fetch requirement is technically met; however, an abandoned field is about 400 m southwest of the site. Since 

winds often come from the southwest and wind speeds are 

frequently over 10 m/s, there might be some situations in 

which the fetch requirement was greater than that generally accepted. During periods of high winds from the 

southwest, this might have resulted in unrepresentative 

data for the site.

Bowen-Ratio Method

The Bowen-ratio method incorporates energy-budget 

principles and turbulent-transfer theory (Brutsaert, 1982, 

p. 210-214). The ratio of sensible- and latent-heat fluxes 

of the energy-budget equation (eq. 1) is known as the 

Bowen ratio (Bowen, 1926). Bowen showed that this 

ratio, P (eq. 6), could be calculated from vertical gradients 

of temperature and vapor over a surface (eq. 7) under certain conditions. Often the gradients are approximated 

from air temperature and vapor-pressure measurements 

taken at two heights above the canopy. The Bowen-ratio 

method assumes that there is no net horizontal advection 

of energy. If there is no net horizontal advection of 

energy, the coefficients (eddy diffusivities) for heat and 

water vapor transport, Kh and KW , respectively, are 

assumed to be equal. With this assumption (eq. 8) and the 

reduction of several terms to form the psychrometric constant (eq. 9), the Bowen ratio takes the form of 

equation 10.

Once the Bowen ratio is determined, the energy-budget equation can be solved for the sensible-heat flux 

(eq. 11) and latent-heat flux (eq. 12). The rate of ET can 

then be determined using the latent-heat flux, latent-heat 

of vaporization of water, and a factor (86.4) that accounts 

for conversion of units (eq. 13a).

Penman-Monteith Method

Estimates of latent-heat flux made with the PenmanMonteith equation require values for vapor pressure 

(eq. 14), saturated vapor pressure (eq. 15), the slope of the 

saturated vapor-pressure curve (eq. 16), and aerodynamic 

resistance to heat (eq. 17) in addition to the energy-budget 

components of net radiation, soil-heat flux, and sensibleheat flux. Field measurements of air temperature, relative 

humidity, and wind speed are needed to determine these 

variables.

Penman (1948) was the first to introduce an evaporation equation for open water (Brutsaert, 1982, p. 215). 

Later, Penman (1956) described an equation to determine 

potential ET over any wet surface, wherein he made the 

assumption that atmospheric resistances to turbulent transport of heat and water vapor were equal. The Penman 

equation (eq. 18) has been refined over the years and can 

estimate potential ET relatively accurately under conditions of unlimited water supply, such as occurs over bodies 

of water and well-watered, physiologically-active crops. 

However, estimates of actual ET made with the Penman 

method for most wildland conditions would be in error 

because of a limited water supply.

Variations of the Penman equation account for the 

resistance due to plant stomatal closure, plant senescence, 

and partially dry soil, and they enable actual ET to be calculated when water is in limited supply. One variation 

developed by Monteith (1963b), termed the PenmanMonteith equation (eq. 19), adds a canopy resistance term 

(eq. 20) to the basic Penman equation.

Canopy Resistance

The canopy resistance is a combination of the resistances to evaporation due to dry soil and to transpiration 

due to stomatal closure or senescence. The canopy resistance is not easily measured, however. In practice, the 

canopy resistance is not measured directly, but determined 

by computing the latent-heat flux by other means, such as 

the Bowen-ratio method, for short periods, and then solving the Penman-Monteith equation for the canopy resistance, which was the approach used in this study. Using

17
this approach, values for the canopy resistance ranged 

from near zero during and shortly after periods of heavy 

rainfall to over 30,000 seconds per meter (s/m) during 

extremely hot, dry periods (Tomlinson, 1994; Tomlinson, 

1995).

For periods when Bowen-ratio data were available to 

calibrate the Penman-Monteith equation for the canopy 

resistance, daily average canopy resistances were computed with canopy resistances calculated for each 

20-minute or 60-minute interval from 8 o'clock in the 

morning to 5 o'clock in the afternoon, when ET was highest (Tomlinson, 1994; Tomlinson, 1995). This daily average canopy resistance was then used in the PenmanMonteith equation for all intervals to compute a daily ET 

value. This procedure allowed ET estimates to be made 

for days when Bowen-ratio data were available for only 

part of the day.

For the Snively Basin site, during periods where no 

Bowen-ratio data were available, such as winter, the canopy resistance was simply estimated (educated guess) 

after taking into consideration data such as soil moisture, 

air temperature, relative humidity, and precipitation. For 

instance, if the relative humidity was 100 percent (fog), if 

there was snow on the ground, or if there was rainfall, the 

canopy resistance was assumed to be zero because of an 

abundant water supply (equivalent to potential ET). For 

subsequent days with above-freezing temperatures and no 

precipitation, canopy resistances were increased with educated guesses on the basis of spring and summer dryingoff conditions, to a maximum of 3,000 s/m. This value 

seemed reasonable on the basis of canopy resistances for 

similar conditions in late summer. These methods of estimation were used because no simple function was found 

correlating canopy resistance with any one variable. The 

best correlation found was with soil moisture, but the r2 

(square of the correlation coefficient) was only 0.63.

For the Turnbull meadow and marsh sites, good 

correlation between soil moisture and canopy resistance 

(Tomlinson, 1995) allowed estimates of canopy resistance 

to be made on the basis of soil moisture for all periods of 

the year where no Bowen-ratio data were available. For 

the Turnbull meadow site's soil moisture-canopy resistance relation, the r2 was 0.82 (Tomlinson, 1995).

Aerodynamic Resistance

In the Penman and Penman-Monteith equations, the 

aerodynamic resistance to heat, rh , is the turbulent resistance between the average height of leaf surfaces and the

height of temperature and wind-speed measurements. 

Heat produced at the leaf surfaces must overcome this 

resistance to arrive at sensor height.

There are a number of ways to calculate the values of 

aerodynamic resistance to heat. These methods commonly use momentum-exchange theory and can produce 

different estimates of the resistance. Momentumexchange theory is complex, and some of the accurate 

measurements needed are difficult to obtain. Some methods are applicable only to neutral periods (sensible-heat 

flux, (H - 0) , others only to stable periods (H<0) , or 

unstable periods (#>0) . A primary goal in this study 

was to use a method that was simple to apply and would 

produce reasonable estimates of ET when used in the 

Penman-Monteith method compared with ET estimates 

obtained from the Bowen-ratio method.

The equation used in this study to estimate rh (eq. 17) 

requires the measurement of wind speed at only one 

height. However, the equation is applicable only during 

neutral conditions. For unstable conditions, a profile stability correction for sensible heat should be added to the 

equation. However, solving for the profile stability correction involves a series of extremely complex iterative calculations. Though using equation 17 without the 

correction for unstable conditions may overestimate rh 

by as much as a factor of two in some conditions 

(D.I. Stannard, U.S. Geological Survey, written commun., 

1992), some investigators have not used the stability correction in their calculations for wildland ET and have produced reasonable results (Duell, 1990). Some researchers 

have applied the correction and found little effect on the 

resulting estimates of rh (Nichols, 1992). Others have 

sought to obtain an empirical equation that incorporates 

this term (Thorn and Oliver, 1977; Marht and Ek, 1984).

For this study, using an rh value in error by as much 

as 100 percent has little impact on the calculations of ET. 

Doubling rh for one time step (20 or 60 minutes) in the 

Penman-Monteith equation for the Snively Basin site 

increased the daily average canopy resistance by 

30 percent and the daily ET estimate by 3.5 percent 

(Tomlinson, 1995). Three and one-half percent is within 

range of the precision errors introduced by the instruments 

(Tomlinson, 1995). Furthermore, the data showed that the 

canopy resistance frequently varied by 30 percent or more 

during each 20 or 60-minute time step, even during neutral 

conditions. Using the stability-correction factor in this 

study would not have resulted in more accurate estimates 

of ET; therefore, it was not used.

18
The 30-percent error in rc is a worst-case scenario; 

the error is likely much less than 30 percent most of the 

time, because neutral conditions are often approximated 

with high wind speeds (D.I. Stannard, U.S. Geological 

Survey, written commun., 1990), which are common at the 

study sites. Hourly average wind speeds frequently range 

from 5 to 15 m/s, occasionally exceeding 15 m/s.

The terms d , z , and z, on the right-hand side of m n °

equation 17 are used in wind-profile equations. The zero 

plane displacement height, d, is the distance, in meters, 

from the surface to the mean height of heat, vapor, or 

momentum exchange. The momentum roughness length, 

zm , in meters, is related to the variance in canopy height. 

The heat-transfer roughness length, zh , in meters, is a 

function of the momentum roughness length. The terms 

d , zm , and zh are difficult to measure, but they may be 

determined graphically from wind profiles or calculated 

through empirical equations. For dense canopies, 

Campbell (1977, p. 38) suggests that d equals 0.64 times 

the canopy height, h . For the Snively Basin site, the 

0.35 m canopy is somewhat less than dense. Therefore, a 

value for d lower than 0.64 times h seems reasonable 

because the level of heat, vapor, or momentum exchange 

will be closer to the surface than for a truly dense canopy. 

.For the Snively Basin site, 0.50 times h was chosen, giving a d of 0.18 m. The value chosen for d does not have 

a major effect on the resulting value for rh in equation 17 

because d is much smaller than the z of 3.0 m. Using a d 

of zero changes the overall rh less than 2 percent from rh 

obtained with a d of 0.18 m, other values being equal. 

For the Snively Basin site, wind-speed data were obtained 

for a 2-week period at 1, 2, 3, and 4 m above the canopy, 

and several wind-speed profiles were plotted to estimate 

zm graphically (Tomlinson, 1994). From these profiles, 

the average value of zm was 0.004 m. This value seems 

reasonable compared with tabled zm values for full-cover 

grasses of 0.001 m to 0.0065 m in Brutsaert (1982, 

p. 114). Campbell (1977, p. 39) states that zh equals 0.2 

zm , so z equals 0.0008 m for the Snively Basin site. 

Wind speed was collected at height z , 3.0 m above the 

canopy. For the Snively Basin site, substituting the above 

values for the variables z > d , zh , zm , and k into 

equation 17 and reducing yields

335 

u

For periods when snow covered the vegetation, d was 

estimated to be zero (flat surface), z was estimated to be 

0.0001 m (Stull, 1988, p. 380), and "h was 0.0002 m. 

Using these values in equation 17 produces

r, =

768

For the sites at the Turnbull NWR, the vegetative canopy is dense, and estimates of the aerodynamic resistance 

to heat can be made on the basis of the height of the vegetation. Thus, Campbell's (1977, p. 38) estimate for d 

(d = 0.64 h) was used. For dense canopies, Campbell 

(1977, p. 39) estimates the momentum roughness length as 

z = 0.13/1 and the heat-transfer roughness length as

For the Turnbull meadow site, canopy height, h , is 

0.91 m, so d = 0.58 m, zm = 0.12 m, and zh = 0.024 m. 

Wind speed, u , was collected at height z = 3.0 m. These 

values in equation 17 give the aerodynamic resistance to 

heat as

5.5

For the Turnbull marsh site, h = 0.61 m, so d = 

0.39 m, z = 0.079 m, and z. = 0.016 m. Using these m n °

values with a z = 3.0 m in equation 17 gives

r, =

113

Snow did not completely cover the plants during the 

winter of 1991-92 at the Turnbull meadow and marsh 

sites; therefore, no adjustments were made for snow conditions at these sites.

For the Black Rock Valley site, no wind-speed profile 

measurements were made to determine zm Estimates of 

z over 0.75-m high greasewood in Nevada were 0.07 m 

from a Leaf-Area-Index method and 0.06 m using 

wind-speed profiles (Nichols, 1992, p. 229-233). From an 

analysis of turbulence over a sparsely-vegetated canopy 

with 1-m-high greasewood in Colorado, zm was estimated 

at 0.05 m (Stannard, 1993, p. 1381-1383). An average of 

0.06 m seems reasonable to use for the Black Rock Valley 

site because of the similarity in canopy height the average shrub height at the Black Rock Valley was 0.81 m 

compared with 0.75 m and 1 m at the Nevada and 

Colorado sites, respectively. The value for zh at the

19
Black Rock Valley site was estimated from In = 2

\ zh) 

(Garratt and Hicks, 1973, fig. 2). This method has been

used at other sparse-canopy sites (Stannard, 1993, 

p. 1383). The zero-plane displacement, d , was estimated 

at zero for the Black Rock Valley site because of the wide 

spacing of the shrubs and sparseness of the grass subcanopy. From the above estimated values for d , z , and zh 

in equation 17 for the Black Rock Valley site,

The scales that weigh the monoliths produce voltages 

that are measured every 10 seconds and averaged every 

hour (Gee and others, 1991). The hourly average voltages 

are converted to weight in kilograms by adding 1 to the 

voltage and multiplying the result by a calibration factor 

(R. Kirkham, Battelle, PNW Laboratories, written commun., 1991). The factors for each lysimeter, in kilograms 

per volt (kg/v), are as follows:

145 

u

Estimates of d , zm , zh , and rh were not made for 

the grass lysimeter or sage lysimeter sites because the 

Penman-Monteith method was not used to estimate ET at 

those sites.

Lysimeter 

number

1

2

3

4

Site

Grass

Grass

Sage

Sage

Factor 

(kg/v)

4650.2527

4646.3382

4651.5727

4645.2527

Weighing Lysimeters

Weighing lysimeters provide the most direct method 

for estimating evapotranspiration (Kirkham and others, 

1991). When the lysimeter soil profile and vegetation type 

and density properly represent the surrounding area, 

lysimeters are considered the standard by which other 

methods, such as Bowen-ratio and Penman-Monteith, are 

evaluated. In their simplest design, lysimeters are containers of soil buried in the ground flush with the soil surface. 

The containers are weighed periodically to measure moisture changes. In some cases, the entire container is 

removed from the ground for weighing.

Monolith weighing lysimeters employ a boxwithin-a-box construction. The inner box contains a 

monolith of soil and vegetation that is as undisturbed as 

possible. The inner box rests on a scale for measurements 

of mass. The outer box acts as a retaining wall for the soil 

profile surrounding the lysimeter. Changes in the mass 

reflect evapotranspiration and precipitation. Monolith 

weighing lysimeters installed and maintained on the ALE 

Reserve by Battelle, Pacific Northwest Laboratories, use 

scales that are sensitive to 50 grams, equivalent to 

0.02 mm of water (Gee and others, 1991). The surface 

dimensions of the inner boxes of the ALE Reserve lysimeters are about 1.5 m2 and range from 1.4 to 1.6 m deep 

(Kirkham and others, 1991).

The difference between the weights can then be converted to ET (negative weight difference) or precipitation 

(positive weight difference) in millimeters as follows: 

divide the weight difference, in kilometers per hour, by 

23,104 cm2 (the area of each lysimeter); multiply the 

result by 10,000 mm/kg/cm2 to obtain a value in millimeters per hour. Sum the hourly weight losses (negative differences) to obtain ET and add the weight gains (positive 

weight differences) to obtain precipitation. An alternate 

method to obtain daily ET is to use the above procedure 

with midnight-to-midnight voltage values, and subtract 

daily precipitation.

Estimating ET and precipitation using the weighinglysimeter data was usually fairly straightforward, but there 

were some exceptions. The process of calculating daily 

ET and precipitation was normally a simple matter of 

summing the hourly weight losses (ET) and weight gains 

(precipitation). On some occasions, however, such as during light rainfalls, precipitation and ET probably occurred 

during the same hour and the net hourly result was the 

greater of ET or precipitation. On other occasions, weight 

gains and losses might have been due to soil or snow 

movement during windstorms or due to animal trespass. 

Also, during very dry periods, the lysimeters showed a 

tendency to gain weight at night, possibly the result of dew 

formation or heating and cooling effects on the lysimeter 

monoliths (R. Kirkham, Battelle, PNW Laboratories, oral 

commun., 1993). Unless these circumstances were very 

clear, it was not possible to account for these phenomena 

in the data.

20
Deep-Percolation Model

Bauer and Vaccaro (1987) developed a deep-percolation model for estimating ground-water recharge and used 

that model to make such estimates for the Columbia 

Plateau (Bauer and Vaccaro, 1990), which includes the 

ALE Reserve and Black Rock Valley. The deep-percolation model computes transpiration, soil evaporation, snow 

accumulation, snowmelt, sublimation, and evaporation of 

intercepted moisture using data for precipitation, daily 

maximum and minimum air temperature, streamflow, 

soils, land use, and elevation. The model (Bauer and 

Vaccaro, 1990) makes water-budget calculations using the 

formula

temperature and precipitation data collected at the site. 

This modification allows the model to be used to calculate 

ET and recharge for more site-specific areas.

The model used user-variable parameters described 

by Bauer and Vaccaro (1990). For the Snively Basin site 

model simulations, the soil type used was a silty loam and 

soil depth for the model was set at 0.6 m (consisting of 

four 0.15-m layers), 0.4 m deeper than the observed 

rooting depth. To compute plant transpiration, the 

model uses Blaney-Criddle crop-growth coefficients (U.S. 

Department of Agriculture, 1967) from growth curves for 

grasses. In the Blaney-Criddle formulation, the growing 

season for plant transpiration is considered to be from last 

frost in the spring to first frost in the fall.

PRCP = RCH + EVINT + EVSOL + EVSNW 

+ PTR + RO + MNT + &SNW + ASNM

where

PRCP = precipitation,

RCH = water percolating below the root zone,

EVINT = evaporation of foliage-intercepted moisture,

EVSOL - evaporation from bare soil,

EVSNW = snowpack sublimation,

PTR = transpiration,

RO = surface runoff,

A/AT = change of moisture on foliage surfaces,

ASNW = change of snowpack, and

ASM = change of soil water in the root zone.

The deep-percolation model makes daily simulations 

for individual grid cells for zones ranging in size from 52 

to 6,200 km2. For most cells, maximum and minimum air 

temperature and precipitation are estimated from selected 

weather stations using a distance-weighted method (Bauer 

and Vaccaro, 1990). If the average daily air temperature 

for the cell was less than 0 C, then all of the precipitation 

for that day was assumed to be snow and was added to the 

snowpack. To estimate ET with the model for the Snively 

Basin site, the model was modified to accept actual air

EVALUATION OF 

EVAPOTRANSPIRATION

Energy-budgets, ET estimates, and water budgets provided a variety of information needed to evaluate ET at the 

grass and sage lysimeter, Snively Basin, Turnbull meadow 

and marsh, and Black Rock Valley sites. For energybudget methods of estimating ET, energy budgets of net 

radiation, soil-heat flux, sensible-heat flux, and latent-heat 

flux were calculated from the collected data. From the 

latent-heat fluxes, which were estimated by the Bowenratio and Penman-Monteith methods, ET estimates were 

made. ET estimates made using the Bowen-ratio latentheat fluxes represent Bowen-ratio ET. ET estimates made 

using the Penman-Monteith latent-heat fluxes represent 

Penman-Monteith ET. ET estimates made using weighing 

lysimeters or the deep-percolation model, which did use 

energy-budget fluxes, are termed, respectively, lysimeter 

ET and model ET.

Bowen-ratio and Penman-Monteith ET agreed well 

with each other for the Snively Basin, Turnbull meadow, 

and Black Rock Valley sites squares of the correlation 

coefficient (r2) were 0.97, 0.96, and 0.91, respectively, for 

the sites. These close agreements were primarily the result 

of using the Bowen-ratio method to calibrate the PenmanMonteith method for the canopy resistance they were 

not independent methods or results. Bowen-ratio ET was 

only 41 percent of lysimeter ET for 6 weeks in April and 

May 1991 at the grass lysimeter site but it was 96 percent 

of lysimeter ET at the sage lysimeter site during 8 days in 

July 1992.

21
For the Snively Basin site, annual Penman-Monteith 

ET differed from annual model ET by 0.4 percent for 1991 

and by 1.2 percent for 1992. However, on a daily, 

monthly, and seasonal basis, the differences between 

Penman-Monteith ET and model ET were usually greater, 

averaging 25.2 percent on a daily basis, 4.0 percent on a 

monthly basis, and 0.7 percent on a seasonal basis. The r2 

of the daily values of Penman-Monteith ET and model ET 

of 0.57 indicated considerable variability.

Water budgets calculated for the Snively Basin site 

and grass and sage lysimeter sites were similar. The 

budgets showed that 100 percent of the precipitation 

became ET in 1991 and about 91 to 98 percent became ET 

in 1992. A water budget for the Turnbull meadow site 

could not be calculated because soil moisture conditions, 

precipitation, and ET prior to May 1991 (when data collection commenced) could not be accurately determined 

(S. Tomlinson, U.S. Geological Survey, written commun., 

1994). No water budgets could be calculated for the 

Turnbull marsh or Black Rock Valley sites because of 

insufficient data.

Energy Budgets

In an energy budget, net radiation equals the sum of 

soil-heat flux, sensible-heat flux, and latent-heat flux 

(eq. 1). The variability of net radiation and the other 

fluxes depended on many conditions such as type, height, 

and extent of vegetation, stage of plant growth, amount 

and density of cloud cover, rainfall, wind speed, season of 

the year, and soil-moisture content. Some plant canopies, 

such as forests, can also store large amounts of heat, which 

can be part of the energy budget. Canopy-heat storage for 

the grass and sagebrush sites was considered negligible 

because of the sparse nature or short height of the canopies.

Net radiation, usually the largest part of the energy 

budget at the eastern Washington study sites, varied 

depending on cloud cover and time of day (figs. 5-9). Net 

radiation curves were smooth for clear days, such as 

July 10 and 12, 1991 (fig. 7), October 3 and 4, 1991 

(fig. 8), and May 7 and 10, 1992 (fig. 6). Net radiation 

measured near zero at sunrise and sunset on clear days, 

peaking around noon. The smoothness of net radiation 

graphs for clear days was also generally reflected in the 

other fluxes. Net radiation curves on partly-cloudy days, 

such as April 10-14, 1992 (fig. 5) and May 12 and 13,

1992 (fig. 6) were irregular due to clouds passing over the 

site. On completely cloudy days, such as April 9, 1992 

(fig. 5), May 8, 1992 (fig. 6), and July 22-23,1992 (fig. 9), 

net radiation and other fluxes were low and somewhat 

irregular, depending on the thickness of the cloud cover. 

Occasionally, irregularities in net radiation were not due to 

clouds. On July 11, 1991 a partial solar eclipse in midmorning caused a dip in the net-radiation curve for an 

otherwise clear day (fig. 7).

During days of precipitation, such as April 9, 1992 

(fig. 5), and July 23, 1992 (fig. 9), soil and atmospheric 

radiation produced little surface warming, so soil- and 

sensible-heat fluxes remained low. Most of the energy 

from net radiation was converted to latent-heat flux, which 

approached or slightly exceeded net radiation.

For periods when the top layer of soil and the air were 

extremely dry, such as October 1-7, 1991 (fig. 8), most net 

radiation became sensible-heat flux, and to a lesser extent, 

soil-heat flux. In this case, sensible-heat flux approached 

the net radiation while latent-heat flux approached zero.

Energy budgets showed other interesting relationships 

between soil, plants, and their environment. These relationships include processes such as frost and advection. 

May 7, 1992 (fig. 6) immediately followed 5 days of high 

latent-heat flux and ET (over 3 millimeters per day) at the 

Snively Basin site due to maximum daytime temperatures 

above 30°C. On May 10 and 11, 1992, the Snively Basin 

site showed similar net radiation and soil-heat flux; however, latent-heat flux on May 11 was only half of what it 

was on May 10. Air temperatures below freezing on the 

mornings of May 11, and May 12, 1992, might have 

stressed the grasses enough to affect their ability to transpire effectively. Afternoon high temperatures were about 

18 Con both days. In another case, an unusual nighttime 

advection condition showed up as a spike of latent-heat 

flux (fig. 7) and ET. At the Turnbull meadow site on 

July 13, 1991, just after midnight, wind speed increased 

from 1.5 to 6 m/s, air temperatures rose from 18.6 to 

24.8 C, and relative humidity dropped from 64 to 

44 percent. A nearby thunderstorm may have advected 

warmer, drier air to the site because, an hour later, some 

rainfall was measured. The phenomenon was large-scale 

because it was also observed at the Turnbull marsh site. 

Other effects such as plant senescence, evaporation at 

night, and seasonal variation were shown by Tomlinson 

(1995).

22
to

U)

600

550

500

450

DC

E 400

111

o

CO

111 

Q

X

350

300

[2 250 

<

Z 200

150

100

50

-50

-100

"1 T

1 T I I 

20-MINUTE AVERAGES:

 NET RADIATION 

SOIL-HEAT FLUX 

LATENT-HEAT FLUX

-- SENSIBLE-HEAT FLUX

16.26 MILLIMETERS OF

RAINFALL MEASURED

FROM APRIL 11-14

7.62 MILLIMETERS OF

RAINFALL MEASURED

ON APRIL 9

I____I J____I J____I J____I J_

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 080

I 9 I 10 I 11 I 12 I 13 I 

APRIL 1992

Figure 5.--Energy budget from the Bowen-ratio method at the Snively Basin site, April 9-15, 1992.
to

600

550

500

450

400

350

300

250

200

§ 150

LLJ 

Q

*, 100

50

QC

P 

LLJ

2 

LLJ

o

CO 

IT 

ff

20-MINUTE AVERAGES: 

NET RADIATION

....... soiL-HEAT FLUX

LATENT-HEAT FLUX

-- SENSIBLE-HEAT FLUX

-50

-100

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 080

I 7 I 8 I 9 I 10 I 11 I 

MAY 1992

Figure 6.-Energy budget from the Bowen-ratio method at the Snively Basin site, May 7-13,1992.
650

to

DC 

LU

LU 

|

o

DC

V)

z

LLJ 

Q

X

ID

I 

20-MINU

NET RADIATION 

SOIL-HEAT FLUX

1.52 MILLIMETERS

OF RAINFALL 

MEASURED AFTER 

MIDNIGHT JULY 13

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 080

I 10 I 11 I 12 I 13 I 14 I 

JULY 1991

Figure 7. Energy budget from the Bowen-ratio method at the Turnbull meadow site, July 10-16, 1991.
oc

LU 

LU

O

CO

450

400

350

300

250

OC

_U 200

150

CO 100

LU 

Q

50

-50

-100

\ \

20-MINUTE AVERAG

NET RADIATION 

SOIL-HEAT FLUX --- 

J____I J____I 

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 080

11 I 2 I 3 I 4 I 5 I 

OCTOBER 1991

Figure 8.--Energy budget from the Penman-Monteith method at the Turnbull meadow site, October 1-7, 1991.
to

700

600

500

tr 

LU

LU 400

o

05

tr 300

200

05

z

LU 100

-100

-200

20-MINUTE AVERAGES:

 NET RADIATION

 - SOIL-HEAT FLUX

 LATENT-HEAT FLUX

--- SENSIBLE-HEAT FLUX

32.26 MILLIMETERS OF

RAINFALL MEASURED

ON JULY 22-23

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 08

I 22 I 23 I 24 I 25 I 26 I 

JULY 1992

Figure 9.--Energy budget from the Bowen-ratio method at the Black Rock Valley site, July 22-28, 1992.
Evapotranspiration Estimates

ET estimates were made on the basis of data from 

energy-budget flux calculations, data from lysimeters at 

the grass and sage lysimeter sites, and results from the 

model. For the Snively Basin, Turnbull meadow, and 

Black Rock Valley sites, the latent-heat flux calculated 

with the Bowen-ratio method was used to calibrate the 

Penman-Monteith equation for the canopy resistance.

Canopy resistances for each time step (20 or 

60 minutes) from about 8 a.m. to 5 p.m. were averaged for 

the day. Latent-heat flux and ET were recalculated with 

the average daily canopy resistance in the PenmanMonteith method for each time step. For these three sites, 

this procedure produced satisfactory daily estimates of 

Penman-Monteith ET, compared with daily estimates of 

Bowen-ratio ET. For example, at the Snively Basin site, 

latent-heat flux and ET estimated with the PenmanMonteith method for the period May 7 to May 13, 1992 

were only 9 percent more than those estimated with the 

Bowen-ratio method. Comparison of the latent-heat fluxes 

made with the Bowen-ratio and Penman-Monteith methods show this similarity at the three sites (figs. 10-12). 

Other examples are shown by Tomlinson (1994) and 

Tomlinson (1995).

Grass and Sage Lysimeter Sites

Precipitation measured by the lysimeters at the grass 

and sage lysimeter sites agreed closely, as did ET for the 

two sites (table 2, figs. 13-14). Total ET from August 20, 

1990 to September 30, 1992 at the grass lysimeter site 

(466 mm) agreed within 1 percent of the ET for the same 

period at the sage lysimeter site (469 mm). Total precipitation measured by the weighing lysimeters at the grass 

lysimeter site for this same period (478 mm) agreed within 

1 percent of precipitation measured by lysimeters at the 

sage lysimeter site (470 mm). On a daily basis, ET values 

at both sites were close, with an r2 of 0.93. This close 

agreement can be expected because the sites are only 

450 mm apart.

Comparisons between Bowen-ratio ET and weighinglysimeter ET for the grass and sage lysimeter sites were 

more variable. For the grass lysimeter site from April 2 to 

May 13, 1991, total ET estimated with the Bowen-ratio 

method was only 41 percent of the total ET measured by 

the lysimeters (table 3). On a daily basis, there was considerable variability; r2 was 0.56. These differences might 

have been caused by instrument error, invalidation of 

assumptions in the Bowen-ratio method resulting from 

processes such as advection of air from unrepresentative 

areas, or conditions in the lysimeters not representing conditions in the larger area surrounding the site.

Although it may be possible that the lysimeters at the 

grass lysimeter site did not always represent true conditions at the site, subsequent investigations by the author in 

1993 and 1994 at the site (S. Tomlinson, U.S. Geological 

Survey, written commun., 1994) suggest Bowen-ratio 

instrument problems were probably responsible for the 

large differences between the Bowen-ratio and weighinglysimeter ET estimates. Worn o-ring seals may have 

allowed leakage of air into the cooled-mirror chamber of 

the DEW-10 system at the grass lysimeter site, which 

would reduce the measured vapor-pressure gradient, and 

thus the latent-heat flux and ET rate.

Without the weighing-lysimeter data for comparison, 

there would have been no indication that the Bowen-ratio 

vapor-pressure data were possibly erroneous. Measurements such as net radiation (two net radiometers were 

used), air temperature and air-temperature difference, soil 

temperature, and soil-heat flux (four soil-heat-flux transducers were used) all appeared reasonable. The vaporpressure values collected by the DEW-10 at the grass 

lysimeter site appeared reasonable; however, the vaporpressure gradients did not. The vapor-pressure gradients 

were extremely small, even during conditions when large 

gradients would have been expected, such as after rainfall. 

Subsequent studies at the grass lysimeter site failed to substantiate large differences between results from the weighing lysimeters and the Bowen-ratio method (S. Tomlinson, 

U.S. Geological Survey, written commun., 1994). Instrument error, possibly in the vapor-pressure measurements, 

was the likely reason for the unusually low Bowen-ratio 

ET estimates, compared with the lysimeter ET estimates. 

(Text continued on p. 45.)

28
QC

LJJ

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LJJ

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LJJ Q.

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LJJ 

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340

320

300

280

260

240

220

200

180

160

140

120

100

80

60

40

20

0

-20 J____I

BOWEN

PENMA

J____I J_

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 080

I 7 | 8 I 9 I 10 | 11 | 

MAY 1992

Figure 10.-Latent-heat flux from the Bowen-ratio and Penman-Monteith methods at the Snively Basin site, May 7-1
CC

E

LU

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to

CC 

LU 

Q_

I

to

LU 

Q

BOWE

PENMA

I I I 

2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 08

I 10 | 11 | 12 | 13 | 14 | 

JULY 1991

Figure 11.-Latent-heat flux from the Bowen-ratio and Penman-Monteith methods at theTurnbull meadow site, 
cc 

P

LLJ 

^

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CC 

LLJ 

Q.

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400

380

360

340

320

300

280

260

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220

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160

140

120

100

80

60

40

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-40 

2400

BOWEN

PENMA

0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 0800 1600 2400 08

| 22 I 23 | 24 | 25 | 26 I 

JULY 1992 

Figure 12.--Latent-heat flux from the Bowen-ratio and Penman-Monteith methods at the Black Rock Valley site
Table2.--Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992

[Precipitation and evapotranspiration estimates for the weighing lysimeters are based on data collected and provided by Battelle, 

Pacific Northwest Laboratories; mm, millimeters; PRG, average precipitation from two weighing lysimeters at grass lysimeter 

site; PRS, average precipitation from two weighing lysimeters at sage lysimeter site; ETG, average evapotranspiration from two 

weighing lysimeters at grass lysimeter site; ETS, average evapotranspiration from two weighing lysimeters at sage lysimeter site; 

TOT, monthly totals of daily precipitation and evapotranspiration; *, partially estimated]

May 1990

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRG

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.30

0.72

0.00

0.00

0.00

0.00

0.00

0.00

0.01

0.35

0.59

2.90

7.39

0.00

0.00

0.00

0.64

1.56

0.05

1.46

3.15

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.26

0.45

0.00

0.00

0.00

0.00

0.00

0.00

0.02

0.42

0.52

2.73

7.35

0.00

0.00

0.00

0.73

1.43

0.09

1.63

2.80

ETG

(mm)

0.57

0.56

0.45

0.49

0.39

0.26

0.30

0.16

0.23

0.32

0.30

0.47

0.52

0.11

0.24

0.24

0.09

0.17

0.18

0.40

0.22

0.75

1.37

2.08

1.08

0.53

0.64

0.59

1.28

0.78

1.35

ETS

(mm)

0.56

0.64

0.64

0.58

0.50

0.33

0.16

0.33

0.33

0.27

0.36

0.39

0.39

0.10

0.26

0.36

0.20

0.24

0.28

0.50

0.23

0.66

1.21

2.01

1.03

0.62

0.66

0.56

1.46

0.68

1.47

PRG

(mm)

0.00

0.00

0.24

0.00

0.00

3.20

0.00

0.00

0.00

0.27

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

June

PRS

(mm)

0.00

0.00

0.24

0.00

0.00

3.14

0.00

0.00

0.00

0.23

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1990

ETG

(mm)

1.80

0.75

0.64

0.50

0.30

1.25

1.38

0.41

0.46

0.58

0.25

0.20

0.19

0.35

0.17

0.23

0.17

0.17

0.16

0.25

0.23

0.02

0.20

0.24

0.19

0.14

0.28

0.14

0.15

0.18

July 1990

ETS

(mm)

1.69

0.81

0.66

0.53

0.30

1.18

1.47

0.33

0.45

0.70

0.30

0.19

0.25

0.39

0.30

0.35

0.30

0.31

0.22

0.37

0.36

0.05

0.37

0.39

0.26

0.20

0.16

0.26

0.23

0.29

PRG

(mm)

0.14

0.23

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.49

1.52

0.12

0.00

0.00

0.00

0.51

1.71

PRS

(mm)

0.06

0.36

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.44

1.60

0.17

0.00

0.00

0.00

0.32

1.23

ETG

(mm)

0.22

0.24

0.22

0.12

0.02

0.12

0.13

0.22

0.13

0.13

0.14

0.13

0.20

0.13

0.13

0.12

0.12

0.13

0.08

0.11

0.08

0.12

0.03

0.45

1.08

0.56

0.16

0.14

0.11

0.17

1.81

ETS

(mm

0.16

0.28

0.12

0.22

0.14

0.13

0.20

-0.24

0.31

0.31

0.29

0.33

0.23

0.26

0.26

0.22

0.14

0.21

0.18

0.21

0.20

0.16

0.10

0.28

1.01

0.61

0.19

0.16

0.29

0.19

1.47

TOT 19.12 18.43 17.12 18.01 3.71 3.61 11.98 13.67 4.72 4.18 7.55 9.10

32
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992-Continued

August 1990

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

0.14

20.06

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.80

0.00

0.00

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.35

0.12

20.37

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.53

0.00

0.00

ETC

(mm)

0.32

0.14

0.12

0.14

0.08

0.10

0.05

0.02

0.04

0.00

0.08

0.07

0.00

0.18

0.00

0.08

0.02

0.06

0.29

0.19

1.32

2.67

1.55

1.03

0.88

0.66

0.62

0.49

1.31

1.06

0.44

ETS

(mm)

0.21

0.16

0.16

0.20

0.23

0.23

0.12

0.15

0.11

0.06

0.09

0.18

0.16

0.11

0.00

0.09

0.00

0.00

0.08

0.07

1.38

2.53

1.28

0.96

0.86

0.61

0.64

0.58

1.07

0.97

0.51

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.0.0

0.00

0.00

September 1990

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.38

0.37

0.37

0.37

0.30

0.26

0.15

0.30

0.27

0.25

0.18*

0.18

0.20

0.22

0.07

0.28

0.09

0.14

0.18

0.21

0.10

0.14

0.16

0.08

0.10

0.14

0.13

0.15

0.17

0.12

ETS

(mm)

0.42

0.41

0.39

0.44

0.40

0.32

0.13

0.31

0.31

0.26

0.31*

0.12

0.15

0.18

0.00

0.15

0.13

0.13

0.16

0.18

0.08

0.11

0.13

0.13

0.14

0.07

0.15

0.13

0.14

0.06

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.90

0.00

0.00

0.00

4.50

0.00

0.24

0.61

0.00

0.00

0.00

1.89

0.19

0.08

0.00

1.80

13.22

0.24

October 1990

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.91

0.00

0.00

0.00

4.55

0.00

0.25

0.71

0.17

0.00

0.00

1.83

0.25

0.00

0.00

1.86

13.06

0.24

ETC

(mm)

0.02

0.13

0.01

0.10

0.12

0.16

0.14

0.11

0.00

0.09

0.08

0.00

0.12

0.91

0.54

0.33

0.13

0.97

1.20

0.43

0.75

0.46

0.24

0.17

0.39

1.12

0.46

0.31

0.21

0.23

1.66

ETS 

(mm

0.00

0.00

0.00

0.19

0.00

0.00

0.00

0.00

0.00

0.08

0.00

0.00

0.00

0.72

0.53

0.15

0.00

0.96

0.99

0.32

0.70

0.63

0.19

0.11

0.17

1.14

0.32

0.39

0.15

0.17

1.69

TOT 22.51 22.37 14.01 13.80 0.00 0.00 6.06 6.04 24.67 24.83 11.59 9.60

33
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992--Continued

November 1990

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRG

(mm)

0.00

0.00

0.00

0.12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.06

0.02

0.00

0.00

0.10

0.16

0.25

0.68

0.62

0.00

0.00

0.00

0.86

0.00

PRS

(mm)

0.00

0.00

0.00

0.17

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.10

0.01

0.00

0.00

0.12

0.11

0.23

0.60

0.60

0.00

0.00

0.00

1.08

0.00

ETC

(mm)

1.12

0.55

0.42

0.63

0.56

0.40

0.32

0.30

0.43

0.40

0.14

0.24

0.33

0.32

0.23

0.22

0.16

0.26

0.18

0.22

0.21

0.34

0.46

0.38

0.88

0.31

0.30

0.18

0.54

0.43

ETS 

(mm)

0.94

0.31

0.34

0.69

0.40

0.27

0.37

0.23

0.69

0.61

0.12

0.15

0.39

0.27

0.17

0.01

0.08

0.21

0.00

0.15

0.01

0.71

0.52

0.59

0.77

0.00

0.23

0.00

0.75

0.25

PRG

(mm)

0.29

0.00

0.00

0.00

0.00

0.00

0.26

0.11

4.09

7.77

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.84

4.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

6.34

0.00

2.36

0.52

December 1990

PRS

(mm)

0.28

0.00

0.00

0.00

0.00

0.00

0.39

0.21

4.14

7.70

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.03

4.65

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

7.47

0.00

2.39

0.32

ETC

(mm)

0.27

0.29

0.09

0.14

0.14

0.09

0.18

0.18

0.08

0.18

0.88

0.24

0.13

0.24

0.19

0.24

0.82

0.77

0.59

0.47

0.23

0.11

0.25

0.23

0.11

0.13

1.34

0.26

0.34

0.18

0.69

ETS

(mm)

0.28

0.09

0.22

0.23

0.07

0.00

0.19

0.18

0.02

0.28

0.74

0.07

0.03

0.11

0.09

0.23

0.86

0.75

0.61

0.12

0.00

0.00

0.00

0.00

0.03

0.05

1.42

0.37

0.25

0.11

0.69

PRG

(mm)

0.00

0.00

0.00

0.00

0.16

1.70

2.18

0.14

2.68

3.90

2.19

1.31

0.00

0.00

0.00

0.58

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.08

0.00

0.00

0.00

0.00

0.21

January 1991

PRS

(mm)

0.00

0.00

0.00

0.00

0.15

1.72

2.23

0.12

3.03

3.94

2.21

2.36

0.00

0.00

0.00

0.47

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.09

0.00

0.00

0.00

0.00

0.18

ETC

(mm)

0.12

0.66

0.19

0.31

0.11

0.20

0.00

0.07

0.09

0.14

0.20

2.88

1.78

1.23

1.01

0.20

0.24

0.08

0.51

0.33

0.24

0.21

0.11

0.31

0.31

0.08

0.14

0.31

0.11

0.10

0.23

ETS

(mm

0.22

0.29

0.23

0.01

0.00

0.15

0.07

0.11

0.10

0.18

0.57

4.06

1.75

1.41

1.29

0.08

0.31

0.01

0.38

0.25

0.11

0.12

0.07

0.23

0.15

0.00

0.11

0.28

0.00

0.02

0.29

TOT 2.81 3.02 11.46 10.23 28.59 30.58 10.08 15.13 16.50 12.50 12.85

34
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992 Continued

February 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRO

(mm)

0.12

1.09

0.43

3.66

1.39

0.14

0.02

0.00

0.00

0.23

0.12

2.32

2.14

0.26

0.00

0.00

0.00

0.00

0.00

0.74

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.07

1.01

0.39

3.57

1.50

0.09

0.08

0.00

0.00

0.31

0.10

1.71

2.12

0.22

0.00

0.00

0.00

0.00

0.00

0.70

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.16

0.50

0.64

0.42

1.45

0.62

0.47

0.47

0.34

0.28

0.19

0.62

0.34

0.70

0.27

1.17

1.06

0.20

0.95

1.16

0.50

0.62

0.60

0.57

0.42

0.51

0.46

0.50

ETS

(mm)

0.24

0.60

0.86

0.70

1.78

0.71

0.57

0.54

0.42

0.36

0.17

0.58

0.36

0.76

0.43

1.24

1.07

0.12

1.04

1.43

0.55

0.67

0.66

0.62

0.54

0.62

0.52

0.52

PRO

(mm)

0.13

6.73

5.04

2.17

0.14

0.00

0.00

0.00

0.18

0.00

1.36

0.93

0.00

0.00

0.23

0.00

0.00

0.19

0.75

0.04

0.13

0.00

0.06

13.37

4.47

0.00

0.00

0.00

0.00

0.00

0.00

March

PRS

(mm)

0.15

6.87

5.08

1.92

0.02

0.00

0.00

0.00

0.13

0.05

1.20

0.77

0.00

0.00

0.24

0.00

0.00

0.11

0.42

0.05

0.15

0.00

0.06

12.69

4.25

0.00

0.00

0.00

0.00

0.00

0.00

1991

ETC

(mm)

0.15

1.12

2.22

1.00

1.74

1.18

1.00

0.82

0.54

0.91

0.58

1.03

0.98

0.74

0.93

0.67

0.67

0.59

0.50

1.25

0.59

0.60

0.42

0.50

0.50

2.38

1.78

1.26

1.33

1.23

1.11

April 1991

ETS

(mm)

0.00

0.78

2.45

0.88

1.98

1.18

1.16

0.92

0.59

1.13

0.56

1.08

1.13

0.73

1.05

0.74

0.79

0.61

0.44

1.10

0.63

0.75

0.43

0.60

0.38

2.67

1.87

1.42

1.36

1.34

1.38

PRO

(mm)

0.00

0.22

0.60

6.13

0.00

0.00

0.00

2.41

0.36

0.00

0.00

0.00

0.00

0.53

5.20

0.09

0.00

0.00

0.00

0.00

0.00

0.00

0.22

0.11

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.00

0.27

0.62

5.93

0.00

0.00

0.00

2.48

0.31

0.00

0.00

0.00

0.00

0.60

5.15

0.03

0.00

0.00

0.00

0.00

0.00

0.00

0.15

0.12

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

1.27

1.10

0.70

1.69

2.66

1.37

1.13

0.88

2.17

1.25

1.43

1.24

1.23

0.93

1.00

2.19

1.54

1.42

1.25

1.22

1.16

1.04

0.77

0.83

0.43

0.65

0.46

0.47

0.58

0.58

ETS

(mm

1.61

1.42

0.76

1.79

2.86

1.35

1.20

0.90

2.36

1.16

1.37

1.14

1.15

0.90

0.97

2.15

1.47

1.30

1.13

1.07

1.11

0.90

0.66

0.79

0.33

0.45

0.42

0.36

0.59

0.51

TOT 12.66 11.87 16.19 18.68 35.92 34.16 30.32 32.13 15.87 15.66 34.64 34.18

35
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992 Continued

May 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRO

(mm)

0.16

0.00

0.35

0.03

0.18

0.00

1.80

3.14

0.00

0.00

0.14

0.36

0.00

0.00

0.00

4.18

3.46

0.58

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.07

0.00

0.19

0.04

0.13

0.00

1.68

3.19

0.00

0.00

0.13

0.37

0.00

0.00

0.00

3.96

3.35

0.53

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.51

0.61

0.43

0.78

0.45

0.29

0.35

2.32

0.81

0.60

0.52

0.67

0.44

0.54

0.41

0.58

1.25

1.47

0.63

0.97

0.92

0.78

0.38

0.51

0.32

0.34

0.33

0.27

0.20

0.24

0.24

ETS 

(mm)

0.42

0.59

0.38

0.66

0.36

0.27

0.23

2.40

0.63

0.48

0.47

0.78

0.39

0.58

0.39

0.69

1.37

1.41

0.48

0.86

0.97

0.70

0.43

0.48

0.28

0.39

0.36

0.40

0.09

0.37

0.33

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

9.62

4.12

0.33

0.00

0.00

0.00

0.00

0.57

0.00

0.05

0.08

0.43

0.00

5.77

12.70

1.16

0.38

0.00

0.00

0.00

0.00

0.00

0.10

0.11

0.00

June

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

9.46

4.11

0.35

0.00

0.00

0.00

0.00

0.51

0.00

0.03

0.10

0.22

0.00

5.14

11.98

1.34

0.26

0.00

0.00

0.00

0.00

0.00

0.12

0.30

0.00

1991

ETC 

(mm)

0.27

0.22

0.27

0.20

0.35

2.85

1.62

1.09

0.91

0.83

0.61

0.44

0.67

0.62

0.41

0.43

0.81

0.30

0.34

2.77

1.47

1.59

1.59

1.13

1.10

0.88

0.94

0.78

0.48

0.92

July 1991

ETS 

(mm)

0.42

0.35

0.30

0.18

0.26

2.94

1.53

1.15

1.00

0.96

0.76

0.45

0.61

0.63

0.40

0.48

0.62

0.34

0.33

2.65

1.69

1.53

1.53

1.10

1.26

1.06

1.12

1.00

0.76

0.95

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.60

0.00

0.00

1.24

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.40

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.62

0.00

0.00

1.20

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.37

ETC 

(mm)

0.79

0.86

0.93

0.77

0.70

0.58

0.62

0.62

0.52

0.54

0.50

0.55

0.82

0.46

0.18

0.97

0.50

0.47

0.38

0.41

0.36

0.39

0.40

0.30

0.23

0.28

0.25

0.29

0.26

0.26

0.37

ETS 

(mm

0.98

1.03

0.97

0.94

0.67

0.57

0.56

0.66

0.53

0.45

0.45

0.46

0.90

0.38

0.07

0.87

0.43

0.30

0.36

0.33

0.34

0.33

0.33

0.29

0.21

0.22

0.25

0.26

0.24

0.21

0.34

TOT 14.38 13.64 19.16 18.64 35.42 33.92 26.89 28.36 2.24 2.19 15.56 14.93

36
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992-Continued

August 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRO

(mm)

0.34

0.00

0.00

0.00

0.00

1.23

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.25

0.00

0.00

0.00

0.00

1.42

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.80

0.29

0.26

0.22

0.11

0.45

0.81

0.30

0.17

0.19

0.14

0.14

0.13

0.11

0.16

0.13

0.14

0.13

0.18

0.17

0.13

0.13

0.12

0.09

0.13

0.11

0.01

0.02

0.12

0.14

0.01

ETS

(mm)

0.66

0.27

0.28

0.21

0.12

0.47

0.91

0.33

0.14

0.16

0.10

0.18

0.14

0.13

0.22

0.22

0.20

0.17

0.38

0.20

0.17

0.15

0.20

0.09

0.07

0.03

0.00

0.00

0.05

0.22

0.04

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.15

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

September 1991

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.15

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.07

0.10

0.11

0.06

0.11

0.00

0.03

0.03

0.12

0.07

0.06

0.06

0.15

0.10

0.07

0.05

0.04

0.06

0.03

0.10

0.09

0.08

0.01

0.01

0.00

0.02

0.04

0.02

0.10

0.03

ETS

(mm)

0.08

0.07

0.09

0.07

0.12

0.06

0.01

0.00

0.00

0.09

0.07

0.07

0.17

0.03

0.08

0.02

0.05

0.07

0.00

0.00

0.02

0.00

0.00

0.09

0.00

0.07

0.01

0.07

0.09

0.04

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.05

0.33

1.77

5.25

2.39

0.04

4.08

0.92

0.00

5.70

October 1991

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.52

0.04

2.25

5.50

2.47

0.09

4.50

0.63

0.00

5.94

ETC

(mm)

0.10

0.12

0.05

0.07

0.09

0.03

0.00

0.05

0.00

0.05

0.03

0.09

0.02

0.04

0.04

0.00

0.14

0.04

0.01

0.00

0.00

0.17

1.12

1.20

0.40

1.06

0.71

0.60

1.13

0.82

0.15

ETS

(mm

0.06

0.06

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.03

0.00

0.12

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.95

1.24

0.32

1.14

0.64

0.30

0.91

0.67

0.05

TOT 1.57 1.67 6.04 6.41 0.15 0.15 1.82 1.54 22.53 23.94 8.33 6.50

37
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992-Continued

November 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRG

(mm)

1.04

0.00

0.11

4.84

5.81

0.22

0.27

0.52

1.02

0.09

0.13

0.00

0.49

0.00

0.00

8.59

0.09

0.15

4.89

0.00

0.00

0.00

0.81

5.54

1.85

10.65

0.00

6.92

0.00

0.00

PRS

(mm)

1.14

0.00

0.11

4.79

5.83

0.24

0.29

0.49

1.04

0.16

0.10

0.01

0.43

0.00

0.00

8.80

0.08

0.18

4.90

0.00

0.00

0.00

0.79

5.43

1.79

10.64

0.00

6.96

0.00

0.00

ETC

(mm)

1.12

0.55

0.42

0.63

0.56

0.40

0.32

0.30

0.43

0.40

0.14

0.24

0.33

0.32

0.23

0.22

0.16

0.26

0.18

0.22

0.21

0.34

0.46

0.38

0.88

0.31

0.30

0.18

0.54

0.43

ETS

(mm)

0.94

0.31

0.34

0.69

0.40

0.27

0.37

0.23

0.69

0.61

0.12

0.15

0.39

0.27

0.17

0.01

0.08

0.21

0.00

0.15

0.01

0.71

0.52

0.59

0.77

0.00

0.23

0.00

0.75

0.25

PRG

(mm)

0.00

0.00

0.00

0.00

5.87

2.79

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.13

2.23

0.00

0.00

3.53

2.22

0.00

0.82

0.00

0.00

0.00

0.21

0.15

0.11

0.04

December 1991

PRS

(mm)

0.00

0.00

0.00

0.00

5.43

2.67

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.22

2.27

0.00

0.00

3.46

2.12

0.00

0.83

0.00

0.00

0.00

0.21

0.16

0.10

0.05

ETC

(mm)

0.93

0.90

0.44

0.75

1.03

0.71

1.29

1.39

1.06

0.48

0.87

0.86

0.35

0.33

0.21

0.12

0.26

0.18

0.22

0.07

0.02

0.18

0.12

0.08

0.27

0.19

0.21

0.18

0.28

0.20

0.14

ETS

(mm)

0.96

1.07

0.60

0.94

0.96

0.84

1.20

1.45

1.16

0.32

0.86

0.95

0.07

0.18

0.01

0.00

0.25

0.20

0.18

0.00

0.00

0.32

0.20

0.16

0.36

0.19

0.24

0.18

0.34

0.19

0.21

PRG

(mm)

0.15

1.75

3.90

0.26

6.31

0.00

0.00

0.00

0.00

0.68

0.00

0.00

0.00

0.00

0.00

4.40

0.00

0.00

0.00

0.00

0.00

0.14

0.58

0.00

0.02

0.15

3.82

4.33

0.17

0.00

0.00

January 1992

PRS

(mm)

0.13

1.74

3.79

0.37

6.46

0.00

0.00

0.00

0.00

0.81

0.00

0.00

0.00

0.00

0.00

4.24

0.00

0.00

0.00

0.00

0.00

0.11

0.72

0.02

0.00

0.17

3.87

4.19

0.19

0.00

0.00

ETC

(mm)

0.16

0.42

0.22

0.53

0.15

0.45

0.64

0.26

0.24

0.06

1.12

0.24

0.18

0.09

0.06

0.23

0.21

0.24

0.28

0.30

0.77

0.29

0.85

0.61

0.88

0.20

0.05

1.82

1.21

0.37

0.66

ETS

(mm

0.15

0.59

0.17

0.71

0.18

0.61

0.50

0.23

0.21

0.06

1.33

0.12

0.16

0.15

0.05

0.26

0.25

0.19

0.30

0.27

0.91

0.26

1.17

0.99

0.96

0.12

0.04

2.02

1.35

0.41

0.74

TOT 54.03 54.20 19.19 19.49 18.10 17.52 14.32 14.59 26.66 26.81 13.79 15.46

38
Table 2.--Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992-Continued

February 1992

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRG

(mm)

0.00

0.00

0.00

0.02

0.18

0.26

1.78

0.23

4.96

0.00

0.00

0.00

0.15

0.28

0.46

0.08

2.50

6.78

8.24

3.99

4.96

0.00

3.06

0.58

0.00

0.00

0.33

0.40

0.00

PRS

(mm)

0.00

0.00

0.00

0.03

0.25

0.45

1.74

0.37

4.98

0.00

0.00

0.00

0.15

0.28

0.45

0.08

2.36

6.19

8.04

3.98

4.76

0.00

2.91

0.60

0.00

0.00

0.24

0.35

0.00

ETC

(mm)

0.87

0.55

0.56

0.35

0.34

0.27

0.14

0.24

0.37

0.77

0.50

0.19

0.29

0.47

0.84

0.62

0.60

0.72

0.53

0.47

1.57

1.67

0.72

0.66

0.55

0.46

0.31

0.41

0.32

ETS

(mm)

1.02

0.54

0.52

0.32

0.34

0.43

0.05

0.43

0.41

0.95

0.70

0.20

0.43

0.55

0.93

0.62

0.67

0.72

0.54

0.62

1.85

1.94

0.71

0.98

0.53

0.58

0.35

0.47

0.38

PRG

(mm)

0.37

0.15

0.43

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.01

2.02

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.22

0.00

0.00

0.00

0.00

0.00

March

PRS

(mm)

0.35

0.18

0.37

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.00

2.27

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.26

0.00

0.00

0.00

0.00

0.00

1992

ETC

(mm)

0.31

0.46

0.64

0.94

1.20

1.20

1.43

1.44

1.23

1.01

1.06

1.09

1.29

1.38

2.10

0.88

1.97

1.42

1.02

1.28

1.33

1.17

1.13

1.33

1.22

1.21

1.30

1.14

1.14

1.41

1.41

April 1992

ETS

(mm)

0.36

0.40

0.79

1.04

1.46

1.44

1.70

1.60

1.39

1.15

1.17

1.27

1.51

1.68

2.46

1.21

2.24

1.77

1.25

1.49

1.50

1.42

1.34

1.58

1.50

1.52

1.82

1.24

1.34

1.61

1.64

PRG

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.04

8.38

0.00

1.93

1.88

12.01

0.00

0.00

0.46

0.00

0.00

0.00

0.00

0.00

0.04

0.02

0.00

0.00

0.00

0.00

0.10

5.30

0.00

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.02

8.29

0.00

1.63

2.60

11.34

0.00

0.00

0.41

0.00

0.00

0.00

0.00

0.00

0.05

0.03

0.00

0.00

0.00

0.00

0.13

5.08

0.00

ETC

(mm)

1.53

1.60

1.32

1.01

0.84

0.98

0.64

0.67

0.11

2.19

1.28

0.96

2.79

2.51

2.13

1.44

2.44

2.21

1.94

1.65

1.73

1.57

1.57

1.57

1.90

1.98

1.58

1.71

0.82

2.91

ETS

(mm

1.83

1. 11

1.64

1.14

0.96

1.00

0.73

0.67

0.12

2.55

1.41

1.06

3.20

2.61

2.27

1.44

2.35

2.06

1.74

1.62

1.55

1.36

1.37

1.30

1.50

1.48

1.19

1.27

0.76

2.59

TOT 39.24 38.21 16.36 18.78 5.20 5.43 37.04 43.89 30.16 29.58 47.58 46.54

39
Table 2. Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.36

0.00

0.00

0.00

0.00

0.00

0.00

May

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.42

0.00

0.00

0.00

0.00

0.00

0.00

1992

ETC

(mm)

1.76

1.67

1.89

1.93

1.82

1.77

1.67

0.67

0.83

1.07

0.75

0.65

0.77

0.87

0.72

0.67

0.60

0.65

0.49

0.49

0.39

0.38

0.46

0.40

0.51

0.51

0.34

0.24

0.28

0.33

0.36

ETS

(mm)

1.35

1.22

1.34

1.31

1.30

1.19

1.21

0.44

0.51

0.83

0.54

0.44

0.63

0.71

0.71

0.60

0.48

0.64

0.54

0.51

0.36

0.38

0.50

0.53

0.53

0.73

0.37

0.28

0.44

0.41

0.49

PRO

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.72

22.80

5.29

0.00

1.09

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.47

0.46

0.00

June

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.57

22.69

4.81

0.00

0.98

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.60

0.37

0.00

1992

ETC

(mm)

0.17

0.34

0.20

0.23

0.21

0.23

0.15

0.22

0.14

0.17

0.41

0.69

2.00

2.08

1.91

2.01

1.36

1.20

1.20

1.05

1.04

0.98

1.00

0.95

0.75

0.57

0.64

0.68

2.29

0.89

July 1992

ETS

(mm)

0.29

0.52

0.28

0.30

0.31

0.36

0.30

0.31

0.20

0.23

0.46

0.72

2.10

2.22

1.99

2.18

1.51

1.47

1.57

1.45

1.34

1.34

1.28

1.16

1.01

0.68

0.76

0.88

2.18

0.91

PRO

(mm)

0.00

0.19

0.00

0.23

0.15

0.00

0.00

0.00

0.00

0.59

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.09

0.00

0.50

0.00

0.38

4.55

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.00

0.14

0.00

0.28

0.16

0.00

0.00

0.00

0.00

0.63

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.12

0.00

0.57

0.00

0.47

4.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.44

0.55

0.51

0.38

0.41

0.36

0.30

0.24

0.34

0.12

0.65

0.35

0.34

0.33

0.34

0.32

0.40

0.33

0.34

0.44

0.23

0.26

1.09

1.57

0.89

0.67

0.54

0.46

0.35

0.37

0.34

ETS

(mm

0.49

0.59

0.60

0.49

0.40

0.41

0.33

0.32

0.43

0.16

0.65

0.38

0.38

0.41

0.34

0.39

0.41

0.38

0.40

0.46

0.36

0.31

1.08

1.33

0.75

0.65

0.49

0.46*

0.37

0.33

Ot.30

TOT 0.36 0.42 25.94 21.52 33.83 33.02 25.76 30.31 6.68 6.62 14.26 14.*

40
Table 2.--Daily and monthly precipitation and evapotranspiration for grass and sage lysimeter sites, May 1, 1990, to 

September 30, 1992 Continued

August 1992

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRG

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

4.29

16.68

0.00

0.07

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.78

10.98

0.00

0.18

0.00

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.31

0.30

0.23

0.20

0.14

0.01

0.18

0.20

0.18

0.21

0.24

0.10

0.27

0.26

0.19

0.22

0.17

0.22

0.16

0.15

0.11

2.35

2.66

1.63

1.25

0.90

0.80

0.66

0.64

0.53

0.44

ETS

(mm)

0.24

0.39

0.20

0.09

0.25

0.22

0.10

0.21

0.14

0.20

0.14

0.16

0.28

0.28

0.19

0.19

0.17

0.17

0.12

0.12

0.13

2.07

1.96

1.26

0.91

0.73

0.65

0.56

0.44

0.33

0.36

PRG

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.53

3.92

0.04

0.00

0.00

0.77

0.00

0.00

0.00

2.76

0.53

0.00

0.00

0.00

0.00

0.00

0.00

September 1992

PRS

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.41

3.83

0.17

0.00

0.00

0.69

0.00

0.00

0.00

2.51

0.47

0.00

0.00

0.00

0.00

0.00

0.00

ETC

(mm)

0.45

0.40

0.44

0.26

0.31

0.28

0.41

0.16

0.31

0.23

0.13

0.27

0.22

0.19

0.50

1.12

0.91

0.62

1.00

0.31

0.26

0.31

0.66

1.13

0.62

0.27

0.38

0.26

0.17

0.24

ETS

(mm)

0.32

0.29

0.24

0.17

0.16

0.13

0.07

0.15

0.15

0.09

0.15

0.08

0.03

0.00

0.48

1.04

0.88

0.43

0.98

0.23

0.33

0.30*

0.52

1.07

0.48

0.23

0.21

0.14

0.17

0.19

TOT 21.04 14.94 15.91 13.26 8.08 12.82 9.71

41
GRA

SAG

JUNE JULY AUG SEPT OCT 

1990

NOV DEC JAN FEB MAR APR MAY 

1991

Figure 13. Daily evapotranspiration from weighing lysimeters at the grass and sage lysimeter sites

1991. Evapotranspiration estimates are based on data collected and provided by Battelle, Pacific N
I I I I I I I I I I I 
Table 3.~Daily and monthly precipitation and evapotranspiration at the grass lysimeter site, April 2 to May 13, 

1991, and at the sage lysimeter site, July 23-30, 1992

[Evapotranspiration and precipitation estimates for the weighing lysimeters are based on data collected and provided by Battelle, 

Pacific Northwest Laboratories; mm, millimeters; PRC, precipitation measured by tipping-bucket rain gage; PRW, average 

precipitation measured by two weighing lysimeters; WL, average evapotranspiration measured by two weighing lysimeters; BR, 

evapotranspiration calculated with the Bowen-ratio method; TOT, total; *, partially estimated; --, no measurement]

Grass lysimeter site

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

._

0.25

0.25

6.10

0.00

0.00

0.00

2.03

0.25

0.00

0.00

0.00

0.00

0.25

5.33

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

April

PRW

(mm)

0.22

0.60

6.13

0.00

0.00

0.00

2.41

0.36

0.00

0.00

0.00

0.00

0.53

5.20

0.09

0.00

0.00

0.00

0.00

0.00

0.00

0.22

0.11

0.00

0.00

0.00

0.00

0.00

0.00

1991

WL

(mm)

1.10

0.70

1.69

2.66

1.37

1.13

0.88

2.17

1.25

1.43

1.24

1.23

0.93

1.00

2.19

1.54

1.42

1.25

1.22

1.16

1.04

0.77

0.83

0.43

0.65

0.46

0.47

0.58

0.58

BR

(mm)

0.68

0.31

1.32

1.15

0.41

0.55

0.20

1.41

0.42

0.24

0.23

0.33

0.32

0.45

0.54

0.30

0.30

0.54

0.33

0.44

0.21

0.29

0.48

0.28

0.27

0.39

0.12

0.26

0.22

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

1.78

2.54

0.00

0.00

0.00

0.25

0.00

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

May

PRW

(mm)

0.16

0.00

0.35

0.03

0.00

0.00

1.80

3.14

0.00

0.00

0.14

0.36

0.00

--

--

--

--

--

--

--

--

--

--

--

--

-

--

--

1991

WL

(mm)

0.51

0.61

0.43

0.78

0.45

0.29

0.35

2.32

0.81

0.60

0.52

0.67

0.44

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

BR

(mm)

0.30

0.22

0.13

0.30

0.31

0.24

0.31

1.11

0.32

0.16

0.36

0.44

0.17

--

--

-

--

--

--

--

--

--

--

--

--

--

--

-

--

Sage lysimeter site

July 1992

PRW WL BR

(mm) (mm) (mm)

_.

..

..

..

--

--

--

..

..

--

..

..

--

..

..

4.25 1.08 1.46

0.00 1.33 0.56

0.00 0.75 0.54

0.00 0.65 0.56

0.00 0.49 0.72

0.00 0.46* 0.56*

0.00 0.37 0.36

0.00 0.33 0.48

..

TOT 14.46 15.87 33.37 12.93 4.57 6.16 8.78 4.37 4.25 5.46 5.24

44
Unfortunately, DEW-10 problems were also partly 

responsible for much erroneous and unreasonable data at 

the sage lysimeter site in 1992. The inexplicable loss of 

calibration on the DEW-10 and consistent icing of its mirror, coupled with data logger problems and animal damage 

to other parts of the Bowen-ratio instruments from May to 

September 1992, allowed only one week of apparently 

accurate data in late July. Although the Bowen-ratio ET 

was 96 percent of lysimeter ET for July 23-30, 1992 

(table 3), the r2 for the daily ET estimates was 0.22, indicating very large variability between the two methods on a 

daily basis. DEW-10 problems may have contributed to 

the poor daily correlation between sage site Bowen-ratio 

ET and lysimeter ET during this period. There is no way 

to be certain, however, because the data appeared reasonable. As at the grass lysimeter site, subsequent investigations comparing Bowen-ratio ET and lysimeter ET at the 

sage lysimeter site in 1993 and 1994 did not show large 

differences between the two methods except in the fall, 

when Bowen-ratio ET averaged six times lysimeter ET 

when sage plants were in bloom (S. Tomlinson, U.S. 

Geological Survey, written commun., 1994).

Snively Basin Site

Seasonal patterns of lysimeter ET at the grass lysimeter site were similar to those of Penman-Monteith ET for 

the Snively Basin site except for late spring (table 4, 

figs. 15-16). During late spring, ET at the Snively Basin 

site was often 2 to 5 times higher than ET at the grass 

lysimeter site. While grasses senesced (grew old) at the 

grass lysimeter site in April or May, they did not senesce 

at the Snively Basin site until June or July. The denser 

cover of grasses at the Snively Basin site, compared with 

the cover at the lysimeter site, reflected a more favorable 

long-term growth environment in Snively Basin. Conditions at the Snively Basin site are wetter and cooler than 

conditions at the grass lysimeter site. Although the 

Snively Basin site is only 5 km from the grass lysimeter 

site, it is 200 m higher in altitude and, during the study 

period (May 30, 1990 to September 30, 1992), received 

13 percent more precipitation than the grass lysimeter site. 

Data collected by Stone and others (1983) showed about 

17 percent more precipitation at Snively Basin than in the 

area around the lysimeters. Coupled with a slightly cooler 

environment, this extra water allowed the grasses at 

Snively Basin a longer growing season than at the grass 

lysimeter site.

During the study period at the Snively Basin site 

(May 1990 to September 1992), latent-heat fluxes and 

ET estimated with the Bowen-ratio method agreed well 

with latent-heat fluxes and ET estimated with the PenmanMonteith method (table 4, fig. 10). The r2 for the Bowenratio and Penman-Monteith ET estimates was 0.95 

(Tomlinson, 1995). The close correlation between the two 

methods was due primarily to using the Bowen-ratio 

latent-heat fluxes to calibrate the Penman-Monteith 

method for the canopy resistance. The results of the methods are not independent.

For the period August 20, 1990 to September 30, 

1992 at the Snively Basin site, totals of model ET agreed 

closely with totals of Penman-Monteith ET. The model 

yielded 512 mm of ET while the Penman-Monteith 

estimates totalled 510 mm. However, on a daily, monthly, 

and seasonal basis, there was much more difference 

(figs. 17-18, table 4). The r2 for the daily values of 

Penman-Monteith ET and model ET was 0.57. Daily estimates of Penman-Monteith ET differed from daily model 

ET by an average of 25.2 percent, with a range of -100 to 

2,400 percent difference. The average of the monthly differences between model ET and Penman-Monteith ET 

was 4.0 percent, but with a wide range of differences:

1990 1991 1992

January

February

March

April

May

June

July

August

September

October

November

December

-

-

-

-

-

-

-

60.9 

(August 20-31)

145

-19.3

-11.0

83.8

19.1

-14.8

-36.2

-39.2

34.4

35.0

-4.7

-64.0

-100

-55.0

-37.8

-46.3

-35.4

-43.1

9.4

28.8

36.6

34.9

-19.7

-39.5

-26.9

--

-

--

(Text continued on p. 60.)

45
Table 4. Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992

[mm, millimeters; PRC, precipitation measured by tipping-bucket rain gage; DPM, evapotranspiration, deep-percolation model; 

BR, evapotranspiration, Bowen-ratio method; PM, evapotranspiration, Penman-Monteith method; RC, canopy resistance; TOT, 

monthly totals of daily precipitation and evapotranspiration; TR, data suggests trace of precipitation; *, partly estimated; #, totals 

for June; --, no measurement]

May- June 1990

Day

May

31

June

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.51

0.00

0.00

0.00

0.00

0.00

6.60

0.00

0.00

0.00

1.27

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

0.97

1.38

0.76

1.99

1.35

0.98

2.06

1.55

0.73

0.62

1.69

1.15

0.75

0.92

1.22

0.93

0.95

0.93

1.01

1.51

0.80

1.13

0.43

0.96

0.87

0.37*

0.27*

0.23*

0.22*

0.29*

0.24*

PM DPM

(mm) (mm)

0.98

1.36

0.80

1.85

1.54

0.84

1.64

1.39

0.94

0.61

1.97

1.27

0.86

0.87

1.25

0.99

1.07

0.99

1.06

1.46

0.62

1.08

0.45

0.86

0.88

0.42

0.32

0.30

0.31

0.39

0.35

PRC

(mm)

0.00

1.52

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

1.27

0.00

0.00

0.00

0.00

0.00

0.00

July 1990

BR

(mm)

0.32*

0.36*

0.30*

0.30*

0.24*

0.24*

0.22*

0.32*

0.29*

0.65*

0.37

0.33

0.32

0.44

0.37

0.37

0.28

0.26

0.40

0.29

0.38

0.38

0.40

0.55

0.98

0.23

0.19

0.27

0.29

0.27

0.26

PM DPM

(mm) (mm)

0.32

0.54

0.36

0.44

0.40

0.27

0.27

0.38

0.38

0.45

0.41

0.38

0.35

0.47

0.39

0.33

0.29

0.29

0.43

0.32

0.36

0.36

0.38

0.61

1.01

0.24

0.21

0.21

0.26

0.29

0.27

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

0.00

TR

0.00

28.19

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.56

0.00

August 1990

BR PM

(mm) (mm)

0.36 0.33

0.30

0.34

0.35

0.36

0.43

0.34

0.21

0.13

0.20

0.18

0.22

0.21

0.21

0.13

0.10

0.26

0.17

0.46

0.16

1.56* 1.49*

2.30*

1.17*

1.04*

0.74*

0.66*

0.56*

0.53*

0.72*

1.18*

0.54*

DPM

(mm

-

-

-

~

~

-

-

-

--

~

~

-

~

-

--

--

-

~

--

0.00

1.52

2.08

1.98

1.68

1.32

1.45

1.55

1.55

2.26

1.07

1.27

TOT 8.38# 28.29# 28.74# 2.79 10.87 11.67 31.75 16.02

46
Table 4.--Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

September 1990

BR PM

(mm) (mm)

0.37*

0.35*

0.21*

0.24*

0.28*

0.28*

0.15

0.23

0.22

0.20

0.24

0.16

0.14

0.18

0.10

0.11

0.14

0.14

0.15

0.13

0.17

0.17

0.14

0.14

0.10

0.14

0.10

0.13

0.12

0.07

October 1990

DPM

(mm)

1.30

1.07

1.02

1.07

1.09

0.89

0.51

0.58

0.58

0.51

0.48

0.36

0.30

0.33

0.23

0.20

0.23

0.23

0.20

0.20

0.20

0.20

0.20

0.18

0.18

0.15

0.13

0.13

0.13

0.10

PRC BR

(mm) (mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.29 1.18

0.00

0.00

0.00

6.35

0.00

0.00

1.02

0.00

0.00

0.00

3.05

0.00

0.00

0.00

2.03

14.22

0.51

PM

(mm)

0.04

0.03

0.03

0.02

0.02

0.02

0.02

0.02

0.02

0.02

0.02

0.02

0.01

0.89

0.65

0.35

0.15

0.64

1.24

0.41

0.70

0.42

0.22

0.19

0.27

0.92

0.45

0.24

0.20

0.55

1.07

DPM

(mm)

0.08

0.05

0.08

0.08

0.05

0.05

0.05

0.05

0.05

0.03

0.03

0.03

0.03

0.46

0.89

0.05

0.03

0.56

0.71

0.10

0.69

0.43

0.08

0.10

1.09

0.25

0.15

0.12

0.71

0.38

0.48

November 1990

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

2.03

0.00

0.00

0.00

1.52

0.00

BR PM

(mm) (mm)

0.94

0.40

0.20

0.30

0.29

0.19

0.14

0.10

0.12

0.14

0.22

0.19

0.19

0.16

0.15

0.15

0.07

0.13

0.09

0.08

0.04

0.08

0.06

0.17

1.04

0.68

0.35

0.16

0.71

0.68

DPM

(mm

0.48

0.25

0.15

0.43

0.26

0.25

0.28

0.20

0.20

0.33

0.38

0.33

0.28

0.18

0.23

0.18

0.13

0.15

0.13

0.13

0.13

0.15

0.13

0.33

0.36

0.26

0.25

0.20

0.30

0.26

TOT 0.00 5.30 12.98 29.47 9.85 7.95 3.80 8.22 7.32

47
Table 4.--Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

5.59

8.64

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.27

2.79

0.00

1.78

0.00

0.00

0.00

0.00

0.25

0.00

3.56

0.25

1.78

1.78

December 1990

BR PM

(mm) (mm)

0.58

0.23

0.25

0.14

0.08

0.09

0.13

0.07

0.09

0.16

0.40

0.23

0.20

0.06

0.24

0.06

0.09

0.09

0.13

0.05

0.06

0.07

0.08

0.07

0.09

0.12

0.41

0.07

0.09

0.07

0.45

January 1991

DPM

(mm)

0.25

0.25

0.23

0.15

0.15

0.15

0.15

0.15

0.26

0.26

0.25

0.25

0.23

0.18

0.18

0.18

0.18

0.25

0.41

0.41

0.66

0.41

0.38

0.28

0.20

0.36

0.18

0.66

0.51

0.33

0.61

PRC BR

(mm) (mm)

0.00

0.00

0.00

0.00

0.00

0.76

1.78

0.00

2.29

1.52

7.88

0.25

0.25

0.51

0.25

0.25

0.00

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PM

(mm)

0.12

0.36

0.10

0.17

0.10

0.07

0.11

0.12

0.16

0.08

0.01

0.58

0.49

0.27

0.41

0.22

0.38

0.23

0.38

0.33

0.21

0.22

0.21

0.09

0.03

0.08

0.10

0.08

0.10

0.05

0.10

DPM

(mm)

0.25

0.18

0.18

0.23

0.18

0.25

0.25

0.30

0.28

0.26

0.25

0.36

0.36

0.26

0.33

0.26

0.25

0.25

0.23

0.18

0.18

0.18

0.15

0.18

0.18

0.20

0.20

0.20

0.18

0.18

0.18

PRC

(mm)

0.00

2.03

0.76

2.03

2.79

0.00

0.00

0.00

0.00

0.00

0.00

1.27

2.79

0.00

0.25

0.00

0.00

0.00

0.00

0.76

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

February 1991

BR PM

(mm) (mm)

0.12

0.94

0.58

0.46

0.99

0.66

0.43

0.25

0.21

0.12

0.05

0.10

0.22

0.19

0.36

1.01

0.66

0.16

0.12

1.62

0.94

0.76

0.52

0.34

0.28

0.34

0.35

0.32

DPM

(mm

0.18

0.51

0.36

0.33

0.56

0.36

0.25

0.30

0.30

0.18

0.18

0.33

0.25

0.28

0.38

0.46

0.38

0.28

0.53

0.71

0.41

0.46

0.51

0.51

0.48

0.56

0.56

0.56

TOT 27.94 4.95 9.10 15.99 5.96 7.10 12.68 13.10 11.16

48
Table 4.--Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.51

9.91

7.11

5.08

0.00

0.00

0.00

0.00

0.00

0.00

1.27

2.54

0.00

0.00

0.00

0.00

0.00

0.51

0.51

0.00

0.00

0.00

0.00

10.92

4.06

4.57

0.00

0.00

0.00

0.00

0.00

March

BR

(mm)

__

--

--

--

--

--

--

--

--

--

--

--

-

--

1.11

1.55

1.23

1.23

0.99

1.00

.76

2.43

1.56

1.45

1.43

1.74

1.60

1991

PM

(mm)

0.16

0.58

0.75

0.59

1.28

0.79

0.63

0.48

0.31

0.40

0.27

1.10

1.30

0.98

0.97

1.01

1.03

0.47

0.73

1.36

1.34

1.12

1.02

0.65

0.64

2.27

1.55

1.16

1.49

1.41

1.53

DPM

(mm)

0.18

0.48

0.71

0.41

0.43

0.46

0.56

0.53

0.51

0.46

0.36

0.64

0.58

0.43

0.51

0.61

0.64

0.63

0.53

0.74

0.81

0.56

0.58

0.58

0.28

0.61

0.97

0.74

0.86

1.19

1.17

PRC

(mm)

0.00

0.51

0.00

4.32

0.00

0.00

0.00

5.84

0.51

0.00

0.00

0.00

0.00

TR

6.10

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

April

BR

(mm)

1.84

2.51

1.25

1.77

2.14

1.64

1.73

1.44

2.49

1.72

2.10

2.01

2.15

2.68

1.71

2.44

2.70

2.04

3.47

3.42

3.83

3.10

2.53

2.18

1.70

2.05

1.88

1.88

1.84

2.57

1.33

1991

PM

(mm)

1.85

2.54

1.11

1.78

2.42

1.76

1.76

1.58

2.50

1.92

2.20

2.09

2.38

2.31

1.33

2.41

2.69

2.02

3.34

3.58

3.80

3.09

2.55

2.20

1.63

2.05

1.92

1.73

1.85

2.16

1.30

May 1991

DPM

(mm)

1.37

0.99

0.81

1.02

1.12

0.81

0.84

1.04

0.94

0.76

1.32

1.50

1.60

1.12

1.17

1.32

1.35

1.57

1.73

2.01

2.26

2.16

1.90

1.14

1.12

1.22

1.30

1.30

1.65

2.01

1.85

PRC

(mm)

0.00

TR

0.00

0.00

0.00

TR

2.54

2.54

0.00

0.00

0.00

0.25

0.00

0.00

0.00

4.06

3.81

0.76

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

1.93

3.03

2.44

1.53

0.79

1.07

0.73

2.24

0.98

1.11

1.04

0.82

1.42

1.82

1.17

0.64

1.02

2.39

0.22

2.21

1.79

0.91

1.01

0.54

0.56

0.61

0.88

1.07

0.74

0.78

PM

(mm)

2.05

3.18

2.58

1.50

0.85

1.00

0.91

2.28

0.99

1.15

1.17

0.96

1.58

2.09

1.26

0.65

1.16

1.83

0.20

2.17

1.78

0.99

1.20

0.72

0.57

0.61

0.80

0.98

0.81

0.83

DPM

(mm

1.91

1.70

1.90

2.16

1.50

1.67

1.63

1.63

1.30

1.68

1.60

1.75

1.52

2.03

2.08

1.35

1.40

1.65

1.14

2.21

2.59

2.54

2.11

1.65

1.50

1.65

1.80

1.98

1.17

1.32

TOT 46.99 29.37 18.75 17.53 66.81 66.55 40.45 13.96 38.82 40.15 53.97

49
Table 4.--Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

June 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

PRC

(mm)

0.00

0.00

0.00

0.00

7.37

6.10

0.00

0.00

0.00

0.00

0.00

0.00

1.02

0.00

0.00

0.00

0.00

0.00

7.11

21.08

1.52

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.25

TR

BR

(mm)

1.39

1.06

0.61

0.54

1.21

3.78

1.49

2.15

0.96

1.39

1.36

0.70

1.02

0.89

0.83

0.83

1.13

0.59

0.81

1.27

1.38

0.79

0.97

0.70

0.95

1.58

1.73

1.56

1.11

2.33

PM

(mm)

1.40

1.05

0.64

0.49

1.30

3.57

1.48

1.87

1.05

1.21

1.26

0.73

0.88

0.87

0.82

0.83

1.12

0.55

0.94

1.50

1.35

0.73

0.97

0.69

0.86

1.53

1.72

1.41

1.20

2.42

DPM

(mm)

2.03

1.85

1.09

1.14

1.40

2.16

1.57

1.80

1.90

2.16

0.97

0.94

1.50

0.97

0.99

0.71

0.97

1.04

1.90

1.22

1.85

1.93

2.51

2.44

2.39

2.11

2.31

2.11

1.32

1.91

0.31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

0.00

0.00

1.27

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

July 1991

BR

(mm)

1.38

1.92

1.64

2.21

1.61

1.95

--

-

--

--

--

0.68

0.62

0.24

0.77

0.74

0.55

0.57

0.65

0.67

--

-

--

--

--

--

--

--

--

--

PM

(mm)

1.25

1.85

1.70

2.17

1.57

1.92

1.58

0.94

0.85

0.46

0.69

0.64

0.68

0.51

0.25

0.73

0.77

0.47

0.49

0.50

0.58

0.44

0.40

0.42

0.34

0.40

0.24

0.24

0.25

0.22

0.41

DPM

(mm)

2.06

2.24

1.96

1.55

1.24

0.99

0.97

0.99

0.84

0.81

0.79

0.74

1.07

0.51

0.36

1.45

0.33

0.38

0.36

0.38

0.30

0.30

0.28

0.25

0.18

0.18

0.18

0.18

0.13

0.13

0.64

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.76

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

August 1991

BR PM

(mm) (mm)

0.25

0.36

0.32

0.35

0.23

0.60

0.70

0.34

0.26

0.14

0.23

0.15

0.14

0.10

0.10

0.16

0.13

0.15

0.14

0.13

0.13

0.15

0.08

0.06

0.08

0.06

0.08

0.03

0.06

0.08

0.08

DPM

(mm

0.10

0.10

0.10

0.08

0.05

0.86

0.33

0.05

0.05

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.03

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TOT 44.45 37.11 36.44 49.19 2.29 23.91 22.78 1.01 5.87 2.11

50
Table 4. Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

September 1991

BR PM

(mm) (mm)

0.04

0.06

0.06

0.09

0.08

0.08

0.05

0.03

0.03

0.05

0.06

0.06

0.04

0.05

0.04

0.06

0.04

0.05

0.06

0.05

0.04

0.03

0.04

0.05

0.06

0.06

0.06

0.05

0.06

0.06

0.63

October 1991

DPM

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PRC

(mm)

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

4.57

2.29

8.38

6.60

4.06

0.25

0.00

4.83

0.00

BR

(mm)

--

--

0.16*

0.20*

0.13*

0.18*

0.12*

0.16*

0.15*

0.15*

0.18*

0.12*

0.12*

0.16*

--

0.12*

0.21*

0.11*

0.15*

0.15*

0.47

0.26

0.11

--

--

--

--

--

PM 

(mm)

0.09

0.15

0.19

0.18

0.23

0.15

0.21

0.11

0.17

0.16

0.18

0.17

0.14

0.15

0.19

0.26

0.12

0.28

0.13

0.16

0.27

0.14

0.67

0.55

0.25

0.30

0.26

0.36

0.60

0.67

DPM

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.61

0.53

0.48

0.38

0.30

0.33

0.26

0.26

0.25

November 1991

PRC

(mm)

0.00

0.00

3.05

3.30

6.86

0.00

0.25

0.51

1.02

0.00

0.00

0.00

0.00

0.00

0.00

8.38

0.25

0.00

6.86

0.25

0.00

0.00

0.76

5.33

1.52

5.59

5.33

0.00

5.08

0.00

BR PM

(mm) (mm)

0.18

0.26

0.71

0.43

0.28

0.21

0.23

0.18

0.24

0.29

0.42

0.87

0.81

0.55

0.19

0.32

1.46

0.80

1.21

0.68

0.52

0.33

0.20

0.19

0.20

0.17

0.55

0.52

0.25

0.34

DPM

(mm

0.25

0.33

0.25

0.30

0.36

0.31

0.26

0.26

0.25

0.25

0.53

0.38

0.25

0.25

0.18

0.30

0.25

0.33

0.25

0.28

0.28

0.26

0.25

0.25

0.31

0.26

0.26

0.26

0.25

0.25

TOT 0.00 1.59 0.00 31.23 8.12 3.65 54.34 13.59 8.45

51
Table 4. Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

5.08

4.32

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.03

0.00

0.00

0.00

3.30

3.81

1.02

0.00

0.00

0.00

0.00

0.00

0.00

0.00

December 1991

BR PM

(mm) (mm)

0.58

0.81

0.64

0.80

1.59

0.39

0.63

0.70

0.73

0.59

0.99

0.74

0.26

0.07

0.12

0.12

0.17

0.21

0.16

0.13

0.24

0.06

0.26

0.28

0.27

0.21

0.15

0.28

0.29

0.27

0.14

January 1992

DPM

(mm)

0.28

0.25

0.20

0.18

0.26

0.26

0.25

0.25

0.31

0.18

0.23

0.18

0.18

0.18

0.18

0.18

0.18

0.26

0.26

0.25

0.20

0.26

0.26

0.25

0.25

0.25

0.23

0.18

0.18

0.18

0.18

PRC BR

(mm) (mm)

0.00

1.27

0.00

3.05

0.00

6.10

0.00

0.00

0.00

1.27

0.00

0.00

0.00

0.00

0.25

4.06

0.00

0.00

0.00

0.00

0.00

0.25

0.76

0.25

0.00

0.00

4.06

4.06

0.00

0.00

0.00

PM

(mm)

0.12

0.37

0.19

0.60

0.11

0.10

0.09

0.03

0.11

0.02

0.99

0.18

0.30

0.25

0.27

0.28

0.44

0.14

0.16

0.19

0.47

0.70

1.00

0.71

0.75

0.16

0.32

1.96

0.97

0.46

0.50

DPM

(mm)

0.18

0.28

0.26

0.26

0.25

0.25

0.25

0.25

0.18

0.26

0.25

0.25

0.18

0.18

0.25

0.28

0.26

0.25

0.18

0.18

0.18

0.25

0.36

0.38

0.38

0.18

0.43

0.33

0.38

0.36

0.46

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

1.54

0.00

5.08

0.00

0.00

0.00

0.00

0.00

0.51

0.00

2.03

7.11

5.84

4.57

5.59

0.00

2.29

0.51

0.00

0.00

0.00

0.25

0.25

February 1992

BR PM

(mm) (mm)

0.65

0.57

0.45

0.48

0.26

0.37

0.23

0.30

0.20

0.52

0.49

0.23

0.46

0.21

0.43

0.67

0.68

1.06

0.42

0.43

2.52

1.63

0.90

0.65

0.37

0.30

0.38

0.40

0.34

DPM

(mm

0.26

0.26

0.25

0.23

0.20

0.18

0.26

0.25

0.25

0.30

0.41

0.23

0.33

0.23

0.38

0.31

0.46

0.33

0.41

0.38

0.74

0.51

0.43

0.41

0.33

0.30

0.23

0.30

0.28

TOT 19.56 12.88 6.92 25.38 12.94 35.57 16.60 9.44

52
Table 4. Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.25

0.00

0.25

0.00

0.00

0.00

0.00

1.02

0.00

0.00

0.00

0.00

0.00

0.25

0.00

0.76

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

March 1992

BR PM

(mm) (mm)

0.28

0.44

0.50

0.94

1.11

1.07

1.10

1.01

1.55

1.09

0.90

0.92

0.93

1.15

0.73

0.59

0.55

0.95

0.71

0.71

0.51

0.56

0.64

0.78

0.53 0.62

0.45 0.58

0.65 0.72

0.43 0.51

0.46 0.56

0.82

1.00

DPM

(mm)

0.33

0.20

0.41

0.46

0.56

0.66

0.69

0.89

0.81

0.81

0.86

0.91

0.99

1.09

0.84

0.89

0.79

0.86

0.89

0.91

0.89

0.92

1.07

1.22

1.12

0.99

1.02

0.74

0.91

1.45

1.65

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

7.62

0.00

1.27

1.27

13.46

0.25

0.00

1.52

0.00

0.00

0.00

0.00

0.00

0.51

0.00

0.00

0.00

0.00

0.00

0.00

8.13

0.25

April

BR

(mm)

._

-

0.78

0.71

0.73

0.55

0.28

--

0.33

0.92

0.50

0.79*

1.32

1.20

0.99

1.34

1.13

1.09

1.14

0.93

0.98

1.03

1.04

0.92

1.26

1.90

1.40

1.51

1.23

1.55

1992

PM

(mm)

1.11

1.14

0.92

0.63

0.68

0.57

0.30

0.55

0.34

0.94

0.59

0.64

1.39

1.39

0.99

1.35

1.27

1.13

1.34

1.06

1.07

1.11

1.15

1.03

1.46

2.10

1.73

1.71

1.27

1.64

May 1992

DPM

(mm)

1.73

2.01

1.30

0.91

0.74

0.84

0.74

1.04

0.58

1.45

1.02

0.97

1.55

1.27

1.55

1.35

1.14

1.42

1.68

1.37

1.24

1.30

1.37

1.78

2.21

2.39

1.88

2.01

1.70

1.45

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

--

--

--

--

--

3.78

1.36

2.12

2.32

1.07

1.10

1.46

--

--

--

--

--

--

--

--

--

--

-

--

--

--

0.36

0.31

0.32

PM

(mm)

2.04

2.54

3.27

3.89

4.31

4.47

4.27

1.47

2.34

2.45

1.17

1.12

1.59

1.73

1.59

1.56

1.67

1.32

0.95

0.91

1.04

1.05

1.38

1.03

0.83

0.61

0.86

0.44

0.42

0.32

0.32

DPM

(mm

1.75

2.31

2.97

3.25

3.43

3.63

3.30

1.42

1.93

2.01

1.60

1.78

2.41

2.97

2.72

2.69

3.00

2.64

2.11

1.73

1.91

2.13

2.59

2.82

2.59

1.80

1.88

1.68

1.73

1.80

1.75

TOT 2.53 24.53 26.83 34.53 32.60 41.99 TR 52.96 72.33

53
Table 4.~Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin site, 

May 31, 1990, to September 30, 1992-Continued

June 1992

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

TR

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

24.38

2.54

0.00

0.51

0.00

0.00

0.00

0.00

0.00

TR

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.25

0.00

BR

(mm)

0.25

0.63

0.26

0.18

0.25

0.33

0.35

~

--

0.20

1.01

-

--

~

~

--

--

--

--

._

1.33

2.04

--

--

--

0.53

0.51

1.42

0.56

PM

(mm)

0.26

0.68

0.26

0.20

0.25

0.37

0.36

0.31

0.15

0.15

0.17

1.15

1.76

1.70

1.73

1.86

1.40

1.99

1.86

1.40

1.50

1.80

2.21

2.16

1.42

0.70

0.71

0.71

1.65

0.70

DPM

(mm)

1.47

1.22

1.02

0.94

0.99

1.02

0.92

0.91

0.58

0.64

0.97

1.83

1.68

1.83

2.31

2.36

2.24

2.62

2.54

2.26

2.11

1.63

1.55

1.27

1.07

0.79

0.92

2.24

0.69

0.58

PRC

(mm)

0.00

0.00

0.00

0.00

0.25

0.00

0.00

0.00

0.00

1.02

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

0.00

3.30

0.00

TR

5.08

0.00

TR

0.00

0.00

0.00

0.00

0.00

0.00

July 1992

BR

(mm)

0.37

0.49

0.47

-

0.59

0.63*

0.41

0.43

0.75

--

0.64

0.87

0.73

--

0.39

0.38

0.46

0.38

0.29

0.56

0.67

--

0.74

0.65

0.77

0.81

0.78

0.54

0.29

0.35

0.34

PM

(mm)

0.51

0.55

0.56

0.38

0.69

0.68

0.51

0.49

0.72

0.30

0.66

0.95

0.76

0.46

0.43

0.40

0.50

0.46

0.29

0.76

0.80

0.54

1.22

0.77

0.75

0.81

0.84

0.61

0.35

0.38

0.38

DPM

(mm)

0.56

0.56

0.56

0.33

0.64

0.38

0.33

0.33

0.33

1.22

0.26

0.31

0.28

0.26

0.23

0.23

0.25

0.20

0.15

1.65

0.28

0.15

1.52

0.43

0.58

0.61

0.58

0.48

0.36

0.41

0.41

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

TR

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.54

3.81

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

August 1992

BR

(mm)

0.34

0.40

0.23

0.32

0.17

--

0.62

0.36

0.23

0.17

0.15

0.25

0.61

0.62

0.65

0.24

0.25

0.28

0.23

0.21

0.25

0.87

0.28

0.52

0.51

0.47

0.22

0.27

0.15

0.17

0.22

PM

(mm)

0.37

0.42

0.28

0.34

0.23

0.19

0.65

0.35

0.26

0.24

0.20

0.31

0.65

0.74

0.68

0.33

0.34

0.33

0.28

0.24

0.40

1.18

0.32

0.56

0.52

0.49

0.26

0.35

0.18

0.19

0.21

DPM

(mm

0.31

0.30

0.23

0.20

0.18

0.10

0.13

0.10

0.13

0.13

0.13

0.08

0.10

0.10

0.08

0.08

0.08

0.05

0.05

0.05

1.52

1.47

0.18

0.20

0.23

0.23

0.23

0.20

0.18

0.13

0.13

TOT 31.74 32.02 43.20 9.65 18.51 14.87 6.35 12.09 7.31

54
Table 4.--Daily and monthly precipitation and evapotranspiration and canopy resistance at the Snively Basin 

site, May 31, 1990, to September 30, 1992-Continued

September 1992

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

4.32

0.00

0.00

0.00

0.25

0.00

0.00

0.00

3.81

1.52

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

0.30

0.25

0.23

0.32

0.23

0.18

0.24

--

0.15

0.11

._

0.19

0.23

--

--

--

0.26

0.26

0.22

0.19

0.34

0.25

0.81

0.72

0.31

0.45

0.26

0.22

0.24

--

PM

(mm)

0.29

0.26

0.26

0.28

0.26

0.20

0.29

0.41

0.20

0.16

0.18

0.26

0.30

0.13

0.53

0.86

0.34

0.36

0.24

0.24

0.45

0.34

0.81

0.97

0.40

0.56

0.34

0.30

0.30

0.38

DPM

(mm)

0.15

0.15

0.13

0.08

0.08

0.05

0.08

0.08

0.08

0.08

0.08

0.05

0.05

0.31

0.76

0.71

0.13

0.18

0.41

0.15

0.15

0.15

1.40

1.14

0.41

0.20

0.15

0.18

0.20

0.20

TOT 9.90 - 10.90 7.97

55
MILLIMETERS IN EVAPOTRANSPIRATION, 

11 m OD 
LA 

-J

CO

DC

LJU

o 

<

£ 2.0kCO

>

LLJ

GRASS LYSIMETER SITE WEIGHING-LYSIMETER 

EVAPOTRANSPIRATION

SNIVELY BASIN SITE PENMAN-MONTEITH 

EVAPOTRANSPI RATION

1.5 -

1.0 -

0.5 -

OCT NOV 

1991

Figure 16. Daily evapotranspiration at the grass lysimeter site and Snively Basin site, October 1, 19

Evapotranspiration estimates for the weighing lysimeters at the grass lysimeter site are based on dat

Battelle, Pacific Northwest Laboratories.
MILLIMETERS IN EVAPOTRANSPIRATION, 

I I I I I I I I I I I I ' I I ' I I I I I I I I I I I I ' I 
C/) 

DC 

LU

LU

LU

4.5

4.0 -

3.5

3.0

Z 2.5

z"

O

E 2-° 

c/)

P

1.5

1.0

0.5

PENMAN-MONTEITH EVAPOTRANSPIRATION 

DEEP-PERCOLATION MODEL EVAPOTRANSPIRATION

OCT NOV 

1991

DEC JAN FEB MAR APR MAY 

1992

JUNE JUL

Figure 18.--Daily evapotranspiration at the Snively Basin site from the Penman-Monteith method and the 

October 1, 1991 to September 30, 1992.
From these differences, several months stand out and 

show some of the major contrasts between the PenmanMonteith and model ET estimates. During late August 

and in September 1990, the deep-percolation model 

yielded much higher ET rates than did the PenmanMonteith method (fig. 17). The 28.19 mm rainfall on 

August 21, 1990, resulted in Penman-Monteith ET of over 

1 mm for just 4 days afterwards, with ET decreasing over 

the next 2 weeks as soils dried (table 4). The model, however, showed ET rates over 1 mm for 16 days after the 

rainfall. This contrast between methods occurred after 

another heavy rain in June 1991 and to a lesser extent in 

June 1992 (table 4, figs. 17-18). These differences probably occur because the model's plant growth curve doesn't 

account for the fact that plants at the Snively Basin site are 

usually not actively growing in summer. Thus, the model 

may overestimate plant transpiration after summer rainfalls when most of the ET is actually due to soil evaporation.

During December 1990 and in August, September, 

and October 1991, model ET was much more or less 

than Penman-Monteith ET, primarily due to the very small 

ET values involved. During these months, daily PenmanMonteith ET was mostly under 0.2 mm. Thus, small 

errors of any kind in the Penman-Monteith data or the 

model inputs could produce large percentages of difference. Also, the model accounted for all input precipitation 

by August 23, 1991, in the model simulation, so zero ET 

was estimated by the model from then to October 21, 

1991. Penman-Monteith ET (table 4) and grass lysimeter 

site ET (table 3) show that ET was rarely zero, even under 

the driest or coldest of conditions, though it may have 

closely approached it.

Another difference between Penman-Monteith 

and model ET estimates is in ET from April to June. The 

Penman-Monteith estimates show large bursts of ET at 

certain times (April 2-26,1991 and May 1-10, 1992) when 

the model shows as much as 50 percent less ET. Later in 

spring (May 22 to June 4, 1991 and May 14 to June 11, 

1992), the model estimates much more ET than the 

Penman-Monteith estimates (table 4, figs. 17-18). These

contrasts may be due to differences between the plant 

growth curve used by the model and the actual growth of 

the grasses at the Snively Basin site. The grasses may 

exhibit bursts of transpiration under favorable spring conditions, then greatly lower their transpiration rate as they 

begin senescing when the available water is nearly used 

up. The transition may take only 2 to 4 weeks, as shown 

from May to June in 1991 and 1992 (table 4). The model's 

growth curve does not incorporate this characteristic, so 

the model partitions the ET at more uniform rates over a 

longer period of time.

The average of the seasonal differences between 

Penman-Monteith ET and model ET was only 0.7 percent, 

but varied seasonally:

1990 1991 1992

Winter

Spring

Summer 88.1

Fall 5.9

-23.6

.3

-20.7

-45.0

-17.5

34.0

-27.4

-

For the above table, summer is defined as the months of 

July to September, fall is October to December, winter is 

January to March, and spring is April to June.

Compared with daily Penman-Monteith ET, daily 

model ET was less during winter, summer, and fall and 

higher in the spring. For summer and fall of 1990, the values reflect ET after a rare heavy summer thunderstorm and 

are not typical of the usually dry summers (1991 and 

1992) and fall (1991). The remaining seasonal variabilities could be caused by (1) the model not incorporating 

wind speed, which can be an important factor in estimating ET with some methods, and (2) errors in the collected 

data or variable inputs used in the model, particularly for 

small ET values.

60
T\irnbull Meadow and Marsh Sites

Seasonal patterns of ET at the Turnbull meadow and 

marsh sites were similar except during mid-summer to 

fall, when the marsh site showed two to three times the ET 

of the meadow site (table 5, fig. 19). During this period in 

1991, the soils at the marsh site were twice as moist as 

soils at the meadow site, in part because of 20 percent 

higher rainfall during the summer at the marsh site but 

perhaps also because of location. Sixty-four percent of this 

higher rainfall was due to a June 28, 1991 thunderstorm 

that produced 16 mm of rainfall at the marsh site but none 

at the meadow site. The marsh site is in an area of 

ground-water discharge, which would contribute to 

moister soils than at the meadow site. Also, the marsh site 

may have received runoff from adjacent upland areas in 

winter and spring.

At the Turnbull meadow site from May to 

October 1991, latent-heat flux and ET (fig. 11, table 5) 

estimated with the Bowen-ratio method agreed well with 

ET estimated with the Penman-Monteith method (table 5). 

The r2 of the two methods was 0.96 (Tomlinson, 1995). 

This close correlation was due almost entirely to the 

agreement of the average daily canopy resistance with the 

canopy resistance measured for each daily 20-minute 

interval. Because the Bowen-ratio method was used to 

calibrate the Penman-Monteith equation for canopy resistance, close estimates of ET from the two methods were 

expected.

Turnbull meadow site ET from mid-October 1991 to 

September 1992 was determined only with the PenmanMonteith method. Daily canopy resistances for the 

Penman-Monteith method derived from a soil moisturecanopy resistance relation developed from Bo wen- ratio 

measurements from 1991 (Tomlinson, 1995). No Bowenratio measurements were made at the Turnbull meadow 

site in 1992. To estimate ET in 1992 with the PenmanMonteith method, it was assumed that the soil moisturecanopy resistance relation for 1992 was the same as for 

1991 (table 5, fig. 19).

The meadow site soil moisture-canopy resistance 

relation was also used at the marsh site to determine 

Penman-Monteith ET because of similar site conditions 

(Tomlinson, 1995). Vegetation, canopy height, topography, net radiation, relative humidity, and soil-heat flux 

all variables that can affect canopy resistance were 

nearly the same at the meadow and marsh sites. Though 

these similarities suggest the soil moisture-canopy resistance relation was the same at both sites, it is possible the 

relation was different for each. If this relation was in error 

or did not apply at the marsh site, then the ET estimates for 

the marsh site might vary from those shown. This error is 

unquantifiable because no Bowen-ratio data were collected at the marsh site to verify the relation.

Black Rock Valley Site

For the Black Rock Valley site, comparisons of 

Bowen-ratio and Penman-Monteith latent-heat fluxes and 

ET showed close agreement. The r2 for the daily estimates 

of Bowen-ratio and Penman-Monteith ET was 0.91. This 

good correlation was expected because the Bowen-ratio 

method was used to calibrate the Penman-Monteith 

method. However, there were some cases where the ET 

estimates of the two methods did not agree well (table 6). 

For instance, from July 26-28, 1992, Penman-Monteith 

ET averaged 44 percent higher than Bowen-ratio ET 

(table 6). The periods of biggest difference in latent-heat 

flux and ET between the two methods appeared to be during high winds at night such as July 26-28, 1992 (fig. 20). 

During such periods, the Bowen-ratio method showed little latent-heat flux, while the Penman-Monteith method 

showed high latent-heat flux.

During the summer, the Black Rock Valley site is subject to diurnal wind patterns because of its location. During the day, upslope wind speeds of 1 to 3 m/s prevailed, 

while at night, downslope wind speeds were 7 to 9 m/s 

(fig. 20). The higher wind speeds at night were probably 

due to the channeling effect of the topography around the 

site.

The Penman-Monteith method seems to be more sensitive to high wind speeds at night than the Bowen-ratio 

method, though both methods take turbulent theory into 

account. This same pattern was noticed at the Snively 

Basin site (Tomlinson, 1995). Also, weighing lysimeters 

showed high ET at night during periods of high wind 

speeds at the grass lysimeter site, while the Bowen-ratio 

method showed little ET (Tomlinson, 1995).

(Text continued on p. 73.)

61
Table 5. Daily and monthly precipitation and evapotranspiration at.the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992

[mm, millimeters; PRC, precipitation, 1\irnbull meadow site; BR, evapotranspiration, Bowen-ratio method, Turnbull meadow site; 

PM1, evapotranspiration, Penman-Monteith method, Turnbull meadow site; PM2, evapotranspiration, Penman-Monteith method, 

Turnbull marsh site; TOT, monthly totals of daily precipitation and evapotranspiration; TR, data suggests trace of precipitation; *, 

estimated or partly estimated; , insufficient data to calculate daily or monthly value]

May 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

--

--

--

--

-

--

--

--

--

-

--

-

0.76

10.16

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

0.00

1.52

0.00

0.00

1.52

0.00

BR

(mm)

--

--

--

--

--

~

--

~

--

--

-

~

-

1.56

1.01

1.42

1.96

3.21

2.58

3.03

2.97

1.84

1.50

2.22

2.62

3.12

3.36

1.53

3.01

PM1

(mm)

--

--

--

--

--

--

--

--

--

--

--

~

--

1.96

1.25

1.26

2.07

125

2.49

3.34

3.06

2.15

1.68

1.94

2.28

3.37

3.27

1.72

3.16

PM2

(mm)

--

-

--

-

--

-

--

--

--

-

--

~

-

2.17

1.74

1.35

2.61

5.57

4.17

5.27

4.72

2.95

2.87

3.20

3.43

4.03

4.39

1.77

4.40

PRC

(mm)

0.00

0.00

0.00

0.00

0.25

5.08

6.60

0.00

0.00

0.00

1.02

0.00

0.25

0.00

0.00

0.00

0.00

0.00

3.56

1.27

0.51

0.00

0.00

4.32

0.25

0.00

0.00

0.00

15.24

0.00

June

BR

(mm)

4.01

4.00

2.46

3.22

1.74

3.60

2.09

2.24

4.18

5.34

3.87

2.37

2.21

2.45

2.90

2.40

3.15

4.22

2.47

1.09

2.33

2.87

2.61

2.96

2.32

3.28

4.53

3.46

1.75

2.60

1991

PM1

(mm)

4.02

3.67

2.50

3.87

2.51

3.51

2.43

2.17

4.26

5.37

4.15

2.45

2.44

2.55

3.19

2.43

2.86

4.29

2.82

1.38

2.45

2.44

2.15

2.92

2.42

3.23

4.52

3.43

1.62

2.54

July 1991

PM2

(mm)

5.24

6.72

5.82

4.77

3.31

3.70

1.82

2.67

4.37

5.84

6.23

3.56

2.71

3.31

3.87

3.77

3.29

4.44

2.94

1.08

2.11

3.02

4.02

2.45

3.09

4.45

5.20

4.02

2.04

3.81

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

0.00

0.00

0.00

1.52

0.00

0.00

0.51

1.78

0.00

0.00

0.00

0.00

0.00

0.00

0.25

3.81

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

4.41*

4.76*

5.73*

5.05*

3.53*

3.87*

4.03*

3.51*

4.05*

4.42*

3.50

3.92

3.62

2.13

1.79

1.41

1.83

2.47

2.00

1.84

1.53

2.02

1.84

1.81

1.97

1.56

1.15

1.12

0.91

0.94

1.20

PM1

(mm)

4.59

4.84

5.13

5.30

4.20

3.24

4.16

3.96

4.23

3.86

3.75

4.21

4.01

2.33

1.82

1.58

2.12

2.56

2.21

2.14

1.82

2.15

2.06

1.87

2.22

1.72

1.28

1.23

0.83

1.09

1.31

PM2

(mm

5.69

6.39

7.21

8.73

7.70

5.90

5.25

5.65

5.09

4.86

5.30

5.92

7.00

3.98

4.18

1.40

2.33

4.45

4.64

4.70

3.64

4.22

4.51

4.12

2.43

2.80

2.91

2.99

3.21

2.93

3.78

TOT 13.96 36.84 38.23 54.64 38.35 88.72 90.59 113.67 8.12 83.92 87.82 143.91

62
Table 5. Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992-Continued

August 1991

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

1.78

0.00

0.00

0.00

TR

9.40

TR

0.00

0.00

TR

0.00

0.76

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

0.00

0.00

0.00

BR

(mm)

1.79

1.44

1.25

1.13

0.75

0.98

1.89

1.86

1.02

1.06

0.83

0.84

0.78

1.05

1.28

1.23

1.12

1.32

0.84

0.86

0.84

0.73

0.75

0.58

0.67

0.73

0.38*

0.69

0.87

0.79

0.41*

PM1

(mm)

2.23

1.39

1.16

1.15

0.82

1.24

1.80

1.83

1.11

1.19

0.86

0.79

0.67

1.09

1.28

1.38

1.30

1.43

1.06

1.03

0.75

0.85

0.85

0.66

0.66

0.83

0.45

0.64

0.86

0.84

0.46

PM2 

(mm)

3.36

3.72

4.00

3.82

0.96

2.73

3.13

4.40

3.92

2.00

2.48

3.39

2.15

2.14

2.92

3.09

3.39

2.82

2.68

2.41

2.41

2.23

1.55

1.51

1.13

1.42

1.03

0.85

1.56

1.81

1.43

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

7.11

0.00

0.00

0.00

0.00

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

September 1991

BR

(mm)

0.23

0.16*

0.22*

0.19*

0.27*

0.24*

0.41

1.29*

0.52*

0.57*

0.28*

0.31*

0.65

0.40*

0.34*

0.42*

0.40*

0.24*

0.27*

0.56*

0.32*

0.61*

--

-

--

--

--

--

--

--

PM1

(mm)

0.23

0.19

0.22

0.20

0.29

0.25

0.47

1.37

0.50

0.61

0.30

0.31

0.64

0.40

0.40

0.52

0.31

0.29

.31

0.65

0.29

0.50

0.47

0.32

0.26

0.25

0.25

0.12

0.18

0.15

PM2

(mm)

0.93

1.00

1.15

1.34

1.43

1.41

0.73

0.68

2.14

2.51

2.28

2.48

1.53

1.67

1.75

1.93

1.55

1.56

1.70

1.33

0.96

0.94

1.04

1.17

1.21

1.30

1.36

0.99

1.13

1.20

October 1991

PRC BR

(mm) (mm)

0.00

0.00 0.26

0.00 0.28

0.00 0.22

0.00 0.26

0.00 0.28

0.00 0.40

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

8.89

1.27

3.05

0.76

0.00

0.00

0.00

0.00

PM1 

(mm)

0.23

0.29

0.33

0.25

0.22

0.26

0.38

0.30

0.30

0.31

0.32

0.38

0.38

0.41

0.43

0.28

0.15

0.19

0.28

0.20

0.15

0.11

0.04

0.04

0.13

0.07

0.08

0.14

0.14

0.07

0.08

PM2

(mm

1.02

0.80

0.74

0.71

0.80

0.76

0.66

0.73

0.84

0.98

0.97

0.77

0.77

0.81

0.87

0.65

0.34

0.38

0.57

0.45

0.35

0.24

0.10

0.08

0.36

0.15

0.16

0.28

0.32

0.20

0.17

TOT 12.19 30.76 32.66 76.44 7.11 11.25 42.40 13.97 6.94 17.03

63
Table 5. Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.25

0.00

0.00

5.84

10.67

0.00

0.00

2.03

0.00

1.52

1.52

0.51

0.00

0.00

0.00

10.16

2.54

0.00

5.59

6.60

0.00

0.51

0.00

6.60

8.64

8.38

7.37

1.78

1.02

0.00

November 1991

BR PM1

(mm) (mm)

0.21

0.16

0.16

0.10

0.15

0.25

0.30

0.28

0.23

0.26

0.32

0.50

0.53

0.30

0.23

0.36

0.90

0.41

0.55

0.79

0.58

0.38

0.32

0.27

0.33

0.33

0.37

0.50

0.80

0.49

December 1991

PM2

(mm)

0.50

0.37

0.38

0.19

0.19

0.32

0.37

0.43

0.34

0.31

0.38

0.71

0.88

0.43

0.39

0.54

0.66

0.44

0.48

0.68

0.47

0.34

0.23

0.21

0.28

0.27

0.27

0.32

0.78

0.44

PRC BR

(mm) (mm)

0.00

0.00

0.00

0.51

13.21

7.62

0.00

0.00

0.00

0.00

0.00

1.52

0.00

0.00

0.00

0.00

0.00

5.59

0.00

1.52

0.00

5.59

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PM1

(mm)

0.38

0.88

0.39

0.47

0.53

0.65

0.68

0.63

1.21

0.76

1.23

1.12

0.80

0.61

0.48

0.40

0.52

0.41

0.19

0.41

0.80

0.38

0.35

0.32

0.57

0.64

0.79

0.57

0.71

0.47

0.65

PM2

(mm)

0.33

0.91

0.33

0.37

0.31

0.44

0.55

0.40

1.05

0.64

1.14

1.17

0.70

0.49

0.40

0.28

0.45

0.29

0.20

0.35

0.52

0.27

0.36

0.37

0.57

0.53

0.59

0.56

0.66

0.35

0.53

PRC

(mm)

0.25

7.37

0.25

6.86

0.51

0.00

0.25

0.00

0.00

0.51

2.54

0.00

0.00

0.00

0.00

5.82

0.00

0.00

0.00

0.00

2.54

2.54

12.45

0.00

0.00

0.00

15.75

4.32

3.56

0.00

0.00

January 1992

BR PM1

(mm) (mm)

0.51

0.52

0.59

0.62

0.53

0.27

0.42

0.42

0.60

0.80

0.50

0.34

0.49

0.36

0.54

0.50

0.41

0.60

0.42

0.44

0.57

0.86

0.84

1.03

1.25

0.79

0.95

1.74

1.01

1.66

3.92

PM2

(mm

0.47

0.32

0.45

0.35

0.40

0.29

0.28

0.51

0.52

0.62

0.33

0.22

0.35

0.28

0.45

0.34

0.29

0.43

0.32

0.31

0.41

0.66

0.52

0.69

0.97

0.65

0.48

0.99

0.38

0.84

1.92

TOT 81.53 11.36 12.60 35.81 19.00 16.11 61.46 24.50 16.04

64
Table 5. Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23-

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.25

2.03

1.27

4.32

0.00

0.25

0.00

1.52

0.25

0.51

0.00

2.29

23.88

0.51

17.78

1.27

0.00

2.54

3.05

0.00

0.00

0.00

0.00

0.00

February 1992

BR PM1

(mm) (mm)

1.37

1.47

1.62

1.35

1.24

1.28

1.05

0.40

0.66

1.26

1.69

1.47

1.25

1.60

0.59

1.31

0.95

0.79

1.45

0.81

1.38

2.35

1.42

0.51

0.93

0.96

0.79

0.68

0.69

March 1992

PM2 

(mm)

0.97

1.13

1.33

1.11

1.01

1.07

1.05

0.32

0.44

1.16

1.15

1.15

1.06

1.23

0.44

1.16

0.68

0.46

1.21

0.62

0.80

2.35

1.16

0.33

0.74

0.75

0.64

0.55

0.55

PRC BR

(mm) (mm)

1.78

0.00

0.51

0.00

0.00

0.00

1.52

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.51

0.51

7.62

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

PM1 

(mm)

1.57

2.00

0.90

1.31

2.22

1.99

1.25

2.28

2.42

2.39

2.51

2.82

3.52

3.24

1.49

2.19

1.11

1.71

2.14

3.03

2.89

2.82

2.77

2.84

3.17

2.37

2.26

2.85

2.71

3.48

3.28

PM2 

(mm)

1.17

1.62

0.68

1.05

1.88

1.77

1.08

2.10

2.21

2.19

2.30

2.49

3.05

2.81

1.26

1.80

1.01

1.39

1.92

2.67

2.66

2.56

2.49

2.58

2.74

2.16

2.34

2.52

2.27

3.16

2.86

April 1992

PRC BR

(mm) (mm)

0.00

0.00

0.00

0.00

0.00

0.25

0.00

0.00

6.35

0.25

0.25

2.79

4.57

0.00

0.00

3.56

2.54

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.54

3.05

PM1

(mm)

3.67

4.22

2.58

2.28

1.52

1.16

1.39

1.99

.56

1.89

1.49

1.10

1.44

2.85

3.51

1.52

2.24

2.85

3.10

2.93

2.17

1.95

2.49

3.64

4.92

4.82

3.34

2.45

1.70

2.88

PM2 

(mm

3.21

3.76

2.48

2.43

1.67

1.26

1.31

1.95

.51

1.92

1.58

1.07

1.75

2.74

3.63

1.67

3.24

4.00

3.52

3.89

2.83

2.91

3.26

4.58

5.31

5.32

4.49

2.97

1.92*

3.26*

TOT 60.45 33.32 26.39 12.70 73.53 64.79 26.15 74.65 84.44*

65
Table 5.--Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

4.57

0.00

0.00

0.00

0.00

0.00

May 1992

BR PM1 PM2

(mm) (mm) (mm)

2.83

2.97

4.53

4.94

5.14

5.60

5.40

2.31

1.92

2.20

1.71

1.95

2.46

2.63

2.21

2.09

2.30

2.05

1.59

0.96

1.08

1.27

1.55

1.48

1.59

1.25

1.73

1.67

1.61

2.00

2.10

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

10.92

9.40

0.00

0.51

0.76

1.27

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

4.32

0.00

June 1992

BR PM1 PM2

(mm) (mm) (mm)

2.19

1.39

1.43

1.03

1.08

1.10

0.91

0.88

0.67

0.80

0.53

0.21

0.85

0.90

1.45

1.21

2.42

3.16

3.35

2.88

3.04

2.89

2.80

2.48

1.97

1.33

1.71

1.20

0.92

1.00

PRC

(mm)

2.54

0.00

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.51

1.02

1.02

2.79

1.27

0.25

0.00

0.00

0.00

0.00

0.00

0.00

0.00

July 1992

BR PM1

(mm) (mm)

1.13

0.86

1.04

0.70

0.67

0.54

0.31

0.32

0.32

0.16

0.21

0.24

0.23

0.23

0.23

0.30

0.39

0.38

0.31

0.27

0.30

0.16

0.14

0.40

1.05

1.06

1.10

1.03

1.12

1.25

1.50

PM2

(mm

--

--

--

--

--

--

--

--

--

--

--

--

--

-

--

--

--

--

--

-

--

--

--

--

--

--

-

--

..

--

TOT 4.57 75.12 12.70 47.78 9.90 17.95

66
Table 5.~Daily and monthly precipitation and evapotranspiration at the Turnbull meadow and marsh sites, May 16, 

1991, to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.25

12.19

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

August 1992

BR PM1 PM2

(mm) (mm) (mm)

1.27

1.05

1.01

0.89

0.64

0.48

0.39

0.45

0.55

0.73

0.86

0.90

1.04

0.98

0.86

0.89

0.89

0.93

0.81

0.65

0.36

0.47

0.90

1.12

1.36

1.55

1.48

1.40

1.36

1.50

1.27

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.29

0.00

0.00

0.00

0.00

0.00

4.57

0.51

0.00

0.00

0.00

0.00

0.00

0.00

0.00

3.81

3.30

0.00

0.00

0.00

0.00

0.00

0.00

September 1992

BR PM1

(mm) (mm)

1.06

1.11

1.18

0.73

0.70

0.62

0.70

0.98

1.17

1.25

0.98

0.82

0.55

0.47

0.36

0.44

0.94

1.07

0.93

0.76

0.93

1.21

0.79

0.54

1.02

0.95

1.24

1.45

1.45*

1.46*

PM2

(mm)

--

--

--

--

--

~

--

--

--

~

--

--

--

--

--

--

--

--

--

--

--

--

--

--

--

-

--

--

TOT 12.44 29.04 14.48 27.86*

67
CO 

CC

HI

1

o 

<

CC 

Q. 

CO

2

HI

TU

TU

MAY JUNE JULY AUG SEPT OCT NOV DEC JAN FEB MAR APR MAY 

Figure 19.--Daily evapotranspiration at the Turnbull meadow and marsh sites, May 15, 1991 to Septem
Table 6.--Daily and monthly precipitation and evapotranspiration for Black Rock Valley site, March 27 to 

September 30, 1992

[mm, millimeters; PRC, precipitation; BR, evapotranspiration, Bowen-ratio method; PM, evapotranspiration, 

Penman-Monteith method; TOT, monthly totals of daily precipitation and evapotranspiration; TR, data suggests trace of 

precipitation; *, estimated or partly estimated; #, precipitation at Moxee City (National Oceanic and Atmospheric 

Administration, 1992); , insufficient data to calculate daily or monthly value]

March 1992

PRC BR PM

Day (mm) (mm) (mm)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26 TR

27 0.00 2.49

28 0.00 1.82

29 0.00 1.60

30 0.00 1.72

31 0.00 1.46*

PRC

(mm)

0.00

0.00

0.00

TR

0.00

0.00

0.00

0.00

9.40#

0.51#

TR

3.30#

15.75#

0.00

TR

3.05#

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.03#

0.00

0.00

April 1992

BR PM

(mm) (mm)

1.82

2.35

2.16

2.02

2.40

1.99

1.16

1.53

1.03

2.88

0.83

1.02*

2.82

3.37

2.41

1.88

2.94

2.96

2.44

1.11

2.35

1.76

2.75

1.67

2.01

2.10

2.19

2.36

1.37

4.37

1.26 1.31

May 1992

PRC

(mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.54

0.00

0.00

0.00

TR

0.00

BR

(mm)

3.29

2.73

3.71

3.83

3.66

3.75

2.92

0.79*

2.30

3.51

2.40

2.82

2.72

2.80

1.06*

--

--

--

--

--

--

--

--

1.03

1.51

--

--

--

--

PM

(mm)

--

-

--

--

--

--

--

--

2.24

3.64

2.51

3.55

2.96

2.91

1.01

0.70

0.91

1.20

0.95

0.47

0.49

0.57

0.62

0.73

1.23

1.58

0.90

0.57

1.22

1.28

TOT 34.04# 64.05 2.54

69
Table 6.~Daily and monthly precipitation and evapotranspiration for Black Rock Valley site, March 27 to 

September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

121

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

PRC

(mm)

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

1.18

0.76

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

7.87

0.25

0.51

0.00

June 1992

BR

(mm)

0.98

--

-

--

--

1.28

1.05

1.05

0.73

1.16

1.54

--

-

~

--

-

1.05*

1.65

2.37

1.12

1.64

~

--

-

1.50

0.98*

1.84

1.43

2.20

2.12

--

PM

(mm)

0.93

1.17

0.56

0.77

0.74

1.49

0.98

0.96

0.70

1.19

1.71

1.93

1.17

0.95

1.45

1.86

1.16

1.82

2.86

1.08

1.79

2.13

1.91

1.84

1.70

1.10

2.33

1.64

2.31

2.34

1.44

PRC

(mm)

TR

0.00

0.00

1.78

0.00

TR

TR

0.00

0.00

TR

0.00

0.00

0.51

0.00

0.00

0.00

0.00

TR

0.25

0.00

0.00

0.76

31.50

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

July 1992

BR

(mm)

1.61

2.58

2.26

3.11

2.55

1.80

1.86

1.42

1.57

1.99

1.25

2.49

2.06

2.13

1.77

1.64

--

--

0.66

0.59*

1.94

0.71*

3.26

2.41

3.12

3.13

2.38

1.71

--

--

0.52

August 1992

PM

(mm)

1.68

2.93

2.80

3.47

2.31

2.03

2.14

1.96

2.09

1.50

1.53

2.85

1.83

2.77

2.25

2.10

2.40

1.67

0.84

0.90

2.13

0.74

2.73

2.69

3.58

3.90

3.68

2:82

1.47

1.49

0.62

PRC

(mm)

0.00

0.00

0.00

0.00

TR

TR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

2.79

3.56

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

BR

(mm)

--

--

0.93

0.65

1.00

0.64

0.69

0.68

--

--

--

0.66

0.50

--

0.51

0.58

0.50

--

--

2.04

1.10

0.82

0.82

0.54

0.55

0.63

0.58

0.52

PM

(mm)

1.59

1.65

1.26

0.90

0.77

1.09

0.74

0.73

0.77

0.95

0.90

0.71

0.70

0.80

0.65

0.78

0.51

0.69

0.49

0.47

0.82

2.04

1.15

0.80

0.87

0.58

0.60

0.63

0.78

0.51

TOT 20.57 44.57 34.29 68.72 6.60 26.55

70
Table 6.--Daily and monthly precipitation and 

evapotranspiration for Black Rock Valley site, 

March 27 to September 30, 1992-Continued

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

September 1992

PRC BR

(mm) (mm)

0.00

0.00

0.00

0.00

0.00

0.00

0.00

TR

0.00

0.00

0.00

0.00

0.00

0.25

6.10

0.00

0.00

0.00

0.51

0.00

0.00

0.00

0.25

2.54

0.00

0.00

0.00

0.00

0.00

0.00

PM

(mm)

0.59

0.69

0.72

0.33

0.41

0.26

0.29

0.25

0.44

0.46

0.27

0.16

0.16

0.14

1.01

1.54

1.37

0.97

1.76

0.61

0.97

0.64

0.36

1.15

0.50

0.27

0.27

0.34

0.31

0.37

TOT 9.65 -- 17.61

71
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2400 2400 2400 2400 2400 2400 2400 2400 2400 2400 

I 26 I 27 I 28 I 29 I 30 I 31 I 1 I 2 I 3 I 

JULY 1992 AUGUST 

Figure 20.-Wind speed at 3 meters above the canopy for the Black Rock Valley site, July 26 to August 6, 1992.
Water Budgets

Long-term ET estimates are important to waterresource managers because ET data, combined with precipitation and surface-runoff data, allows them to make 

estimates of recharge to subsurface systems: the soil profile, the unsaturated zone, and ground water. Precipitation 

(PR ), ET, surface runoff (RO ) from other areas, and 

recharge (RCH) to subsurface systems make up the water 

budget at the eastern Washington sites:

PR + RO = ET+RCH

When estimates of precipitation, surface runoff, and ET 

are known, the remainder of the water budget is the 

change in subsurface systems.

Annual water budgets were calculated for the grass 

and sage lysimeter sites and the Snively Basin site. A 

water budget for the Turnbull meadow site was not possible because estimates of precipitation, ET, and soil moisture that occurred in the year before the study began could 

not be accurately made (S. Tomlinson, U.S. Geological 

Survey, written commun., 1994). Water budgets could not 

be developed for the Turnbull marsh site and the Black 

Rock Valley site because of limited data and unknown 

antecedent conditions. For the Snively Basin, grass lysimeter, and sage lysimeter sites, water budgets were formulated for 1991 and 1992 with collected data. Water 

budgets were also formulated for the Snively Basin site 

with ET estimates from the deep-percolation model. The 

water budgets for 1991 for the Snively Basin, grass and 

sage lysimeter sites showed that 100 percent of the precipitation became ET; for 1992, about 91 to 99 percent of the 

precipitation became ET.

Grass and Sage Lysimeter Sites

Water budgets for the grass and sage lysimeter sites 

were determined for two periods: August 20, 1990 to 

September 30, 1991 (1991 water budget) and October 1, 

1991 to September 30, 1992 (1992 water budget). At the 

beginning and end of these periods, ET and surface soil 

moisture were near zero (table 2). In each case, daily ET 

was about 0.1 to 0.2 mm, and surface (upper 0.15 m) soil 

moisture measured about 2.5 percent. On the basis of 

lysimeter data, cumulative ET and precipitation for the

grass and sage lysimeter sites were nearly identical 

(fig. 21). Also, the overall ratios of ET-to-precipitation for 

the lysimeter sites for 1991 and 1992 agreed within 

8 percent of the ratios determined for the Snively Basin 

site.

The water budgets for the grass and sage lysimeter 

sites were determined in two ways. In the first method, ET 

and precipitation were calculated for each lysimeter site 

for each day (values from the two lysimeters at each site 

were averaged), and the totals of each were accumulated 

for the water-budget periods. In the second method, the 

actual lysimeter weights at the beginning and end of the 

water budget periods were compared (with values from 

the two lysimeters at each site averaged). The second 

method allowed an annual budget not affected by all of the 

lysimeter weight changes not caused by precipitation or 

ET, such as blowing and drifting snow or animal trespass. 

In each case, the two methods agreed within 4 percent of 

each other for both lysimeter sites. The water budgets presented assume that runoff equals zero for the periods of 

study at the lysimeter sites and that water is able to drain 

freely from the bottoms of the lysimeters.

On the basis of daily ET and precipitation values for 

1991 at the grass lysimeter site, lysimeter ET and precipitation totalled 215 mm and 212 mm, respectively. This 

gave a 101 percent ET-to-precipitation ratio, indicating 

that all precipitation was returned to the atmosphere as ET 

and that there was no subsurface-system recharge. For the 

1991 water budget, the ratio of the ending lysimeter 

weight (September 30, 1991) to the beginning weight 

(August 20, 1990) was 100 percent, indicating no net 

change in moisture storage in the soil monolith. This 

showed that precipitation and ET were equal, and no 

recharge occurred during the period.

For 1992 at the grass lysimeter site, the weighing 

lysimeters measured daily totals of 251 mm of ET and 

266 mm of precipitation. This gave a 94.4 percent 

ET-to-precipitation ratio, indicating about 15 mm, or 

5.6 percent of the precipitation, might have become subsurface-system recharge (which includes stored soil moisture). From the actual lysimeter weights, the ratio of the 

ending weight (September 30, 1992) to the beginning 

weight (October 1,1991) was 98.0 percent. This indicated 

that 3.6 percent less water became subsurface-system 

recharge than that showed by the water budget which used 

daily ET and precipitation totals.

73
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I I I I I I T I I I I I I I I I ( I \ 

GRASS LYSIMETER SITE, CUMULATIVE PRECIPITATION 

SAGE LYSIMETER SITE, CUMULATIVE PRECIPITATION 

GRASS LYSIMETER SITE, CUMULATIVE EVAPOTRANSPIRATION 

SAGE LYSIMETER SITE, CUMULATIVE EVAPOTRANSPIRATION

l l l I I I l l 

AUG SEPT OCT NOV DEC JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC JAN FEB MAR 

1990 | 1991 | 

Figure 21. Cumulative precipitation and evapotranspiration from weighing lysimeters at the grass and sage 

August 20, 1990 to September 30, 1992. Evapotranspiration and precipitation estimates are based on data c

provided by Battelle, Pacific Northwest Laboratories.
Daily totals of ET and precipitation for 1991 at the 

sage lysimeter site were almost identical to those at the 

grass lysimeter site. The weighing lysimeters at the sage 

lysimeter site measured 214 mm of ET and 211 mm of 

precipitation. This gave a 101 percent ET-to-precipitation 

ratio, indicating that all precipitation had been returned to 

the atmosphere as ET, with no subsurface-system 

recharge. From the actual sage lysimeter weights for the 

1991 water budget, the ratio of the ending weight 

(September 30, 1991) to the beginning weight (August 20, 

1990) was 100 percent, indicating no net change in moisture storage in the soil monolith. ET and precipitation 

were equal during this period.

For 1992 at the sage lysimeter site, the weighing 

lysimeters measured daily totals of 255 mm of ET and 

259 mm of precipitation. This gave a 98.5 percent 

ET-to-precipitation ratio, which indicated that about 

4 mm, or 1.5 percent of the precipitation, might have 

become subsurface-system recharge. From the actual sage 

lysimeter weights for the 1992 water budget, the ratio of 

the ending weight (September 30, 1992) to the beginning 

weight (October 1, 1991) was 99.3 percent. This ratio 

indicated almost no recharge to subsurface systems.

On the basis of the lysimeter data for 1992, about 

2.7 percent more subsurface-system recharge was estimated for the grass lysimeter site than for the sage lysimeter site. This might indicate that subsurface-system 

recharge would be greater in grass-covered areas than in 

sagebrush-covered areas, a condition supported by some 

studies (Link and others, 1990). However, the water budget estimates might also indicate that the sage plants in the 

lysimeters at the sage lysimeter site were root-bound by 

the lysimeters. If the sage plants were root-bound, they 

would tend to use all available water in the lysimeters (just 

like a root-bound potted plant) and would appear stressed 

during dry periods because the roots could not spread further to obtain more-deeply stored water. A root-bound 

condition may be indicated by the observation that plants 

in the lysimeters had fewer live branches and sparser 

blooms than plants outside the lysimeters. However, for 

the grass and sage lysimeter sites, water budget results 

were fairly close. The 2.7 percent difference in recharge 

could also simply be instrument or measurement error. 

More years of data-collection and comparison at the grass 

and sage lysimeter sites would be needed to more definitely assess the root-bound effect.

Snively Basin Site

Seasonal patterns of precipitation and ET at the 

Snively Basin site were similar to those of the grass lysimeter site (fig. 22). The greatest precipitation was received 

in winter and early spring and most of the annual ET 

occurred in spring. Also, the least precipitation and ET for 

the year usually occurred in late summer or early fall. 

Because the Snively Basin site is only 5 km from the grass 

lysimeter site, this similarity was expected. However, 

amounts of precipitation and ET were different. The 

Snively Basin site averaged 13 percent more precipitation 

and 9 percent more ET than the grass lysimeter site from 

August 20, 1990 to September 30, 1992.

For the Snively Basin site, water budgets were calculated for August 20, 1990, to September 30, 1991, and for 

October 1, 1991, to September 30, 1992. These budgets 

used ET estimates from collected data and from results of 

the deep-percolation model. August 20, 1990, was chosen 

as a starting point for the water budget because antecedent 

conditions were such that change in surface soil-moisture 

storage and ET were near zero. The last precipitation over 

2 mm prior to August 20, 1990 occurred on June 6, surface soil moisture averaged only 2.4 percent, and grasses 

were completely dormant. Similar conditions existed on 

September 30, 1991, and September 30, 1992, so water 

budgets were analyzed separately for August 20, 1990, to 

September 30, 1991 (1991 budget), and October 1, 1991, 

to September 30, 1992 (1992 budget).

A tipping-bucket rain gage measured precipitation at 

the Snively Basin site for the entire period of study. The 

gage worked well except during sub-freezing weather, 

when the tipping mechanism stuck because of ice on the 

mechanism or snow did not penetrate the screen of the collection funnel. When temperatures rose above freezing, 

however, the snow melted and was recorded. During the 

winter of 1990-91, the tipping-bucket gage measured only 

about half the precipitation that fell as snow; this was 

shown by a comparison of the Snively Basin tippingbucket precipitation data with precipitation data collected 

by a storage gage about 30 m away. Precipitation data for 

the winter was supplemented by data from this storage 

gage to provide more accurate precipitation amounts and 

timing. The winter of 1991-92 was unusually mild with 

little snow, so no adjustments for snowfall were made to 

the collected data. During high winds, however, the gage 

may not have measured precipitation accurately because it 

was not shielded (Linsley and others, 1982).

75
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I I I I II I I I I I I I I I I I I I I I I I I I I I I I I I || I I I I I I I I I I I I I 

I ' ! IM I I I I I I I I I I I I I I I I I I I I I I I I I I I 
Although dewfall and trace precipitation were not 

measured at the Snively Basin site, dewfall is estimated at 

less than 5 percent of the precipitation on the ALE 

Reserve (Rickard and others, 1988). To account for 

unmeasured trace precipitation, dewfall, and wind effects 

on the tipping-bucket gage, the measured precipitation 

was increased by 5 percent, on the basis of Rickard and 

other's (1988) estimate. The 5 percent increase in precipitation at the Snively Basin site was distributed evenly over 

all the precipitation events during the period of study. The 

measured precipitation was multiplied by 1.05 to estimate 

the precipitation used in the Snively Basin water budget. 

Five percent was considered a conservative estimate of the 

unmeasured precipitation; possibly it was higher, as was 

shown at other sites. Tipping-bucket precipitation was 

9.5 percent less than weighing-lysimeter measured precipitation at the grass lysimeter site in April and May 1991 

(Tomlinson, 1995). Also, tipping-bucket precipitation 

averaged 12 percent less than precipitation measured by a 

storage gage near the Turnbull meadow site in 1991 and 

1992 (S. Tomlinson, U.S. Geological Survey, written commun., 1994).

Surface runoff was assumed to be zero for the period 

of study. Only three storms exceeded 20 mm of precipitation (August 21, 1990, June 20, 1991, and June 12, 1992, 

table 4), and the overland runoff at the Snively Basin site 

was assumed to be very low because the soils were very 

dry and likely to readily absorb any rainfall.

At the beginning of the water budget period 

(August 20, 1990), soil moisture in the top 0.15 m of the 

profile at the Snively Basin site was measured at 

2.4 percent, and ET for the day was estimated at 0.1 mm. 

One day later, 28.19 mm of rainfall was measured there. 

A steep slope occurred in the cumulative ET plot (fig. 23) 

after the August 21 rainfall, indicating high daily ET. This 

steep slope was followed by a leveling-off period in late 

September and early October 1990, when ET was near 

zero. These leveling-off periods occurred during late summer or early fall for each year that data were collected at 

the Snively Basin site and coincided with near-zero ET 

and surface soil moisture under 3 percent. In 1991, this 

near-zero leveling-off period occurred from August until 

late October (table 4, fig. 23). In 1992, the near-zero 

leveling-off period occurred from late August to midSeptember (table 4), although it was not as marked as it 

was in 1991.

Precipitation from October to February each year 

added moisture to the soil profile, while ET remained 

fairly low because of low net radiation, low temperatures, 

and an inactive plant canopy. For the 1991 water budget, 

only 16 percent of the ET occurred from October to 

February, while in the 1992 water budget, 26 percent of 

the ET occurred from October to February. The larger 

percentage in the 1992 water budget reflects the higher ET 

loss during the warmer winter of 1991-92, compared with 

the previous winter.

From March to July each year, plants quickly used up 

the water stored in the soil profile, and the slope of the 

cumulative ET plot steepened dramatically (fig. 23). In 

the 1991 water budget, 76 percent of the ET occurred from 

March to July; April alone accounted for 25 percent. In 

the 1992 water budget, 65 percent of the ET occurred from 

March to July, with May accounting for 21 percent of the 

annual total ET.

From August to September, the cumulative ET plot 

leveled out again as rainfall occurred only infrequently 

and soil moisture approached 2.5 percent. The slope of 

the plot became steeper during August and September 

only for short periods following major rainfalls, such as 

that on August 21, 1990.

The annual total of ET calculated with the PenmanMonteith method agreed well with annual totals of ET 

from the model within 0.4 percent in 1991 and 

1.2 percent in 1992, although daily, monthly, and seasonal 

values varied. The 1991 water budgets included 260 mm 

of precipitation and totalled 262 mm of Penman-Monteith 

ET and 261 mm of model ET. This gave a 101 percent 

ET-to-precipitation ratio with the Penman-Monteith 

method and 100 percent ET-to-precipitation ratio with the 

model. Results from both methods indicated that all precipitation from August 20, 1990, to September 30, 1991, 

was returned to the atmosphere as ET that is, no water 

was available for recharge to subsurface systems. The 

1992 water budgets included 274 mm of precipitation and 

totalled 248 mm of Penman-Monteith ET and 251 mm of 

model ET. This gave a 90.5 percent Penman-Monteith 

ET-to-precipitation ratio and a 91.6 percent model 

ET-to-precipitation ratio. Recharge to subsurface systems 

for the 1992 budget was estimated at 26 mm from the 

Penman-Monteith estimates and 23 mm from the model 

ET estimates. The deep-percolation model results indicated that this recharge occurred during February 1992.

77
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

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The closeness of the 1992 recharge estimates calculated by the Penman-Monteith method and model could be 

coincidence, however. There are uncertainties in instrumentation precision, precipitation catch, the winter 

Penman-Monteith ET estimates, and the often large daily 

disagreement between deep-percolation model and 

Penman-Monteith ET estimates. Given these uncertainties, actual recharge at the Snively Basin site for 1992 

could have been somewhat larger or smaller than recharge 

estimated by the two methods. Perhaps 1992 recharge at 

the Snively Basin site was as low as estimates from lysimeter data at the nearby grass and sage lysimeter sites (4 to 

15 mm).

Although there are some uncertainties in all the methods used the weighing lysimeters at the grass and sage 

lysimeter sites, the Penman-Monteith method (which 

incorporated Bowen-ratio measurements) and the deeppercolation model for the Snively Basin site all estimated nearly the same magnitude of recharge results. 

Results from all the methods indicated that recharge at the 

Snively Basin site was very low: probably zero in 1991, 

and less than 10 percent of the annual precipitation in 

1992.

SUMMARY AND CONCLUSIONS

Evapotranspiration (ET) was evaluated at six sites in 

Benton, Spokane, and Yakima Counties, Washington. 

Three sites were located on the Arid Lands Ecology 

Reserve in Benton County: one at a dense-canopy grassland in Snively Basin (Snively Basin site), one at sparsecanopy grassland adjacent to a pair of weighing lysimeters 

(grass lysimeter site), and one at a sagebrush grassland 

adjacent to two weighing lysimeters (sage lysimeter site). 

Two sites were located on the Turnbull National Wildlife 

Refuge in Spokane County: one at a full-canopy grassland 

in a meadow (Turnbull meadow site); the other at a 

full-canopy grassland near a marsh (Turnbull marsh site). 

The sixth site was located in a sagebrush grassland in the 

Black Rock Valley in Yakima County (Black Rock Valley 

site).

The periods of study used at the six sites varied, ranging from 5 months at the Black Rock Valley site to more 

than 2 years at the Snively Basin, grass lysimeter, and sage 

lysimeter sites. The periods of study were May 1990 to 

September 1992 for the Snively Basin, grass lysimeter, 

and sage lysimeter sites, May 1991 to September 1992 for 

the Turnbull meadow site, May 1991 to April 1992 for the 

Turnbull marsh site, and March to September 1992 for the 

Black Rock Valley site.

The Bowen-ratio method, Penman-Monteith method, 

weighing lysimeters, and a deep-percolation model were 

used to estimate ET at the study sites. Evapotranspiration 

and energy-budget fluxes were calculated with the Bowenratio and Penman-Monteith methods for the Snively Basin 

site, the Turnbull meadow site, and the Black Rock Valley 

site. Daily ET for the Snively Basin site was also estimated with a deep-percolation model for the Columbia 

Plateau. The Bowen-ratio method and weighing lysimeters were used at the grass and sage lysimeter sites. The 

Penman-Monteith method was used at the Turnbull marsh 

site.

Daily ET at the sites ranged from less than 

0.2 millimeter during very dry or cold periods to more 

than 4 millimeters after heavy rainfall or during periods of 

peak transpiration. At all sites, peak ET occurred in 

spring, coinciding with plant growth, and the lowest ET 

occurred in late summer and winter, coinciding with plant 

dormancy and extremely hot or cold temperatures. About 

two-thirds of the ET for the year occurred from March to 

July while only about one-fifth occurred from October to 

February at the Snively Basin site.

Daily ET estimated with the Bowen-ratio method and 

the Penman-Monteith method agreed very well at the 

Snively Basin, Turnbull meadow, and Black Rock Valley 

sites. The close correlation was expected, however, 

because the Bowen-ratio method was used to calibrate the 

Penman-Monteith method for the canopy resistance. 

Squares of the correlation coefficients (r2) were 0.95 at the 

Snively Basin site, 0.96 at the Turnbull meadow site, and 

0.91 at the Black Rock Valley site. The r2 for the Black 

Rock Valley site was lower than the other two sites primarily because windier conditions at night produced higher 

estimates of ET at night than those estimated with the 

Bowen-ratio method.

ET at the grass and sage lysimeter sites agreed well 

with each other on a daily and annual basis. The r2 on the 

daily values was 0.93. Totals of ET for the period 

August 20, 1990 to September 30, 1992 for both sites 

were very close, with 466 mm estimated at the grass site, 

and 469 millimeters estimated at the sage site.

Ratios of ET-to-precipitation at the Snively Basin 

site (100 percent in 1991 (August 20, 1990 to 

September 30, 1991) and 91 percent in 1992 (October 1, 

1991 to September 30, 1992) agreed well with the same 

ratios at the grass and sage lysimeter sites (100 percent in 

1991; 94 to 99 percent in 1992). However, there were 

some differences in daily and seasonal ET estimates. During winter, high ET spikes were shown by weighing lysim79
eters during high winds, while less ET was shown by the 

Penman-Monteith method at the Snively Basin site. During late spring, ET was usually much lower at the grass 

and sage lysimeter sites than at the Snively Basin site. 

This was due to 13 percent higher precipitation at the 

Snively Basin site than at the lysimeter sites. The wetter 

environment at the Snively Basin site allowed grasses to 

continue growing well into June, while at the lysimeter 

sites, the grasses were senescing in late April and May and 

usually dormant or perished by June.

For the Snively Basin site, deep-percolation model 

ET estimates did not agree well with Penman-Monteith 

ET estimates on a daily or seasonal basis; however, they 

did agree well on an annual basis. The r2 for the daily values was 0.57, indicating much variability. Model ET differed from Penman-Monteith ET during several periods. 

After heavy summer rainfalls, model ET was usually 

higher than Penman-Monteith ET. During the winter, 

model ET was usually less than Penman-Monteith ET. 

During early to mid-spring, the model showed much lower 

ET than the Penman-Monteith method did; later in the 

spring, the model showed much higher ET than the 

Penman-Monteith method. During windy periods, model 

ET was less than Penman-Monteith ET. The differences 

averaged out on an annual basis, however, as annual ET 

totals estimated by the two methods agreed within about 

1 percent of each other for 1991 and 1992. The differences between Penman-Monteith ET and model ET were 

probably due to (1) differences between the plant growth 

curve used by the model and the actual growth of grasses 

at the Snively Basin site; (2) the model not incorporating 

wind speed, which is an important function in the PenmanMonteith method; and (3) errors in the collected data or 

variable inputs to the model, particularly for small ET values.

Water budgets for the Snively Basin, grass lysimeter, 

and sage lysimeter sites were formulated from estimates of 

precipitation, ET, and surface runoff. Surface runoff was 

assumed to be zero for all sites because the most intense 

rainfalls occurred during periods when the soil was very 

dry and probably could absorb most of the rainfall. Trace 

precipitation, dewfall, and precipitation not measured by 

the tipping-bucket rain gage, because of wind effects, were 

estimated at 5 percent of the measured precipitation for the 

Snively Basin site. For the water budget at the Snively 

Basin site, 5 percent was added to the measured precipitation to provide more accurate estimates. No adjustments 

were made for precipitation measured by weighing lysimeters at the grass and sage lysimeter sites.

For the Snively Basin site, annual totals of PenmanMonteith ET estimates agreed with annual totals of model 

ET by 0.4 percent in 1991 and 1.2 percent in 1992. For 

the 1991 budget, Penman-Monteith ET totalled 

101 percent and model ET totalled 100 percent of the 

260 millimeters of precipitation. In the 1992 budget, 

Penman-Monteith ET totalled 90.5 percent and model ET 

totalled 91.6 percent of the 274 millimeters of precipitation. Recharge for the 1991 budget was zero; for 1992, it 

ranged from 23 millimeters with model ET estimates, to 

26 millimeters with Penman-Monteith ET estimates. The 

model indicated the 1992 recharge occurred in February. 

The close agreement of the recharge to subsurface systems 

estimated by the Penman-Monteith method and the model 

was probably coincidence, given the variability of the 

daily and seasonal ET estimates.

Water budgets based on weighing lysimeter data at 

the grass and sage lysimeter sites agreed within 1 percent 

of each other for 1991 and within 5 percent of each other 

for 1992. For 1991, all of the measured precipitation 

(212 millimeters at the grass lysimeter site and 

211 millimeters at the sage lysimeter site) became ET. For 

1992, 94 to 98 percent of the 266 millimeters of precipitation became ET at the grass lysimeter site, while 98 to 

99 percent of the 259 millimeters of precipitation became 

ET at the sage lysimeter site.

No water budgets were formulated for the Turnbull 

meadow and marsh sites or Black Rock Valley site 

because of the inability to determine antecedent precipitation, ET, and soil moisture, in addition to the short periods 

of study.

In conclusion, this report makes the following findings:

1) The Bo wen-ratio method can be used to calibrate the 

Penman-Monteith method for the canopy resistance 

as an alternate method of calculating ET at grass and 

sage sites in eastern Washington. However, the 

canopy resistances determined in this way may 

include error from a number of sources, such as 

instrument error, and should be viewed as a 

calibration factor between the two methods. 

Furthermore, this canopy resistance varies 

tremendously depending on site conditions. Thus, 

actual ET estimated by an independent method such 

as weighing lysimeters or the Bo wen-ratio method 

will be needed to calibrate the Penman-Monteith 

method on a daily basis. The Penman-Monteith 

method cannot be used to make accurate daily 

estimates of ET without calibration for the canopy

80
resistance during spring, summer, and fall. 

Reasonable estimates might be made with the 

Penman-Monteith method during the winter because 

the canopy resistance can often be estimated because 

of frequent rain, snow, or fog. At other times during 

winter, errors in estimating canopy resistance may 

average out and should not be of great concern 

because winter ET is very low and only a small 

percentage of the annual ET.

2) The Penman-Monteith method appears to estimate 

higher ET during windy periods than does the 

Bowen-ratio method. Thus, the Penman-Monteith 

method may be more sensitive to higher wind speeds 

than the Bowen-ratio method. Weighing-lysimeter 

data show that high ET can occur during periods of 

high wind, even at night, when net radiation provides 

no source of energy.

3) For the grass lysimeter, sage lysimeter, and Snively 

Basin sites on the Arid Lands Ecology Reserve, the 

ratio of ET to precipitation on an annual basis was 

nearly the same at each site for 1991 and 1992 even 

though the amounts of precipitation and ET were 

different. In each case, 90 to 100 percent of the 

precipitation became ET. Greater precipitation at the 

Snively Basin site, compared with the lysimeter sites, 

appeared to result in higher ET, but not necessarily 

increased recharge to subsurface systems (soil 

moisture, the unsaturated zone, and ground water).

4) For the Snively Basin site, the Columbia Plateau 

deep-percolation model estimated almost the same ET 

as the Penman-Monteith method on an annual basis 

but not on a daily, monthly, or seasonal basis. 

Observed differences may have been partly due to the 

model not incorporating wind speed in estimating ET 

and to the model using unrepresentative growth 

curves for grasses in predicting transpiration. The 

model and the Penman-Monteith method estimated 

almost the same amounts of annual recharge to 

subsurface systems in 1991 and 1992, but this could 

have been coincidence. Further comparisons of this 

model need to be made at sites in the Columbia Basin 

to better assess whether or not the model could be 

used to estimate daily, monthly, or seasonal ET and 

recharge.

5) Although precipitation is difficult to accurately

measure, ET and precipitation are the most important 

components of the water budget in eastern

Washington. Because of wind effects on tippingbucket gages as well as no measurements of trace 

precipitation or dew, measured precipitation at the 

eastern Washington sites was almost certainly 

underestimated by the tipping-bucket gages. 

Estimates of the under-measurement range from 5 to 

12 percent at these sites. Weighing lysimeters 

probably can accurately measure precipitation in most 

cases except during periods when precipitation and 

ET occur during the same measurement interval and 

cancel each other out. This error is probably small 

most of the time, because ET is usually near zero 

during precipitation, but it could be very large in some 

cases, such as when high precipitation at the 

beginning of a measurement interval was followed by 

high ET during the rest of the measurement interval.

6) ET is difficult to accurately estimate with the

Bowen-ratio method in semiarid areas such as eastern 

Washington. The Bowen-ratio instruments used in 

this study were prone to failure when used over long 

periods of time because of inexplicable calibration 

drift on cooled mirrors, possible leaks in the cooledmirror chamber, icing of the mirror caused by dew 

points below freezing (not uncommon in eastern 

Washington), failure of electronic and mechanical 

components such as the pump motor for the cooled 

mirror, and damage to sensors caused by animals and 

hail. Additionally, vapor-pressure gradients may be 

too small to accurately measure with available 

instruments. Unfortunately, many of the vaporpressure measurement errors were not readily 

apparent from the collected data. Precision of all 

instruments is also a factor in determining ET and 

may cause ET estimates to vary by plus or minus 

12 percent.

7) Caution should be used when determining water 

budgets and making ET estimates in semiarid, and 

perhaps other, areas. Two or more completely 

independent methods may be required at a site to 

accurately assess ET and determine a water budget. 

In the study at the Snively Basin site, the 

measurements by the weighing lysimeters at the 

nearby weighing-lysimeter sites helped provide more 

confidence in the Bowen-ratio and Penman-Monteith 

measurements that were made. Only when results 

from two or more methods agree can one be 

reasonably sure that the instruments are making 

accurate, representative measurements.

81
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