Effects of Potential Future Warming on 

Runoff in the Yakima River Basin, 

Washington

Scientific Investigations Report 2008–5124

Prepared in cooperation with the Bureau of Reclamation

U.S. Department of the Interior

U.S. Geological Survey
Cover: Photograph of U.S. Geological Survey Hydrologist, John Vaccaro, standing 

in Cabin Creek near Easton, Washington. (Photograph taken by Mark Mastin, U.S. 

Geological Survey, 1998.)
Effects of Potential Future Warming on 

Runoff in the Yakima River Basin,

Washington

By Mark C. Mastin

Prepared in cooperation with the Bureau of Reclamation

Scientific Investigations Report 2008–5124

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Mastin, M.C., 2008, Effects of potential future warming on runoff in the Yakima River Basin, Washington: U.S. 

Geological Survey Scientific Investigations Report 2008-5124, 12 p.
iii

Figures

Figure 1. Map showing major reservoirs managed by the Bureau of Reclamation, 

meteorological and streamflow-gaging stations, and subbasins simulated 

by the four watershed models, Yakima River Basin, Washington ..................... 3

Figure 2. Graph showing comparison of irrigation season (April through August) runoff 

at American River near Nile, and snow-water equivalent at Bumping Ridge on 

April 1 for water years 1979, 1981, and 1984–2006, Yakima River Basin, 

Washington ................................................................................. 4

Figure 3. Graphs showing simulated mean monthly runoff for base conditions and 

plus one and plus two scenarios at selected sites in the Yakima River Basin, 

Washington ................................................................................. 6

Tables

Table 1. Monthly changes in air temperature for the plus one and plus two climate 

change scenarios used in the watershed model simulations, Yakima River 

Basin, Washington ........................................................................ 4

Table 2. Simulated changes in mean monthly runoff and mean annual runoff from the 

base condition for the plus one and plus two scenarios at selected sites in the 

Yakima River Basin, Washington ......................................................... 7

Table 3. Simulated snowmelt for four watershed models for base conditions and 

plus one and plus two scenarios, water years 1981–2005, Yakima River Basin, 

Washington ................................................................................. 8

Contents

Abstract ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Yakima River Basin Study Area ..........................................................................................................2

Imposed Climate Changes............................................................................................................................4

Watershed Models ........................................................................................................................................5

Simulated Runoff Results .............................................................................................................................5

Summary..........................................................................................................................................................8

References Cited............................................................................................................................................9

Appendix A. Mean Monthly and Annual Unregulated Runoff Simulated for Base 

Conditions and Two Climate Change Scenarios, Plus One and Plus Two, for 

Indicated Subbasins ......................................................................................................................11
iv

Conversion Factors and Datums

Conversion Factors

Multiply By To obtain

acre 4,047 square meter (m2

)

acre-foot (acre-ft) 1,233 cubic meter (m3

)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

foot (ft) 0.3048 meter (m)

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F= (1.8×°C) +32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C= (°F-32)/1.8.

Datums

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 1929).

Altitude, as used in this report, refers to distance above the vertical datum.
Abstract 

The Bureau of Reclamation has implemented a longterm planning study of potential water-storage alternatives in 

the Yakima River Basin, which includes planning for climate 

change effects on available water resources in the basin. 

Previously constructed watershed models for the Yakima 

River Basin were used to simulate changes in unregulated 

streamflow under two warmer climate scenarios, one 

representing a 1oC increase in the annual air temperature over 

current conditions (plus one scenario) and one representing 

a 2oC increase in the annual air temperature over current 

conditions (plus two scenario). Simulations were done for 

water years 1981 through 2005 and the results were compared 

to simulated unregulated runoff for the same period using 

recorded daily precipitation, and minimum and maximum air 

temperatures (base conditions). Precipitation was not altered 

for the two warmer climate change scenarios. 

Simulated annual runoff for the plus one and plus two 

scenarios decreased modestly from the base conditions, but the 

seasonal distribution and the general pattern of runoff proved 

to be highly sensitive to temperature changes throughout the 

basin. Seasonally increased runoff was simulated during the 

late autumn and winter months for both the plus one and plus 

two scenarios compared to base conditions. Comparisons at 

six principal regulatory locations in the basin showed that 

the maximum percentage increases in runoff over the base 

conditions during December to March varied from 24 to 

48 percent for the plus one scenario and 59 to 94 percent for 

the plus two scenario. During late spring and summer months, 

significantly decreased runoff was simulated at these sites 

for both scenarios compared to base conditions. Simulated 

maximum decreases in runoff occurred during June and July, 

and the changes ranged from -22 to -51 percent for the plus 

one scenario and -44 to -76 percent for the plus two scenario. 

Differences in total annual runoff at these sites ranged from 

-1.4 to -3.9 percent for the plus one scenario and from -2.5 

to -8.2 percent for the plus two scenario. The percent change 

of the monthly mean runoff for both scenarios from the base 

conditions at many points in the basin will be used in a watermanagement model developed by the Bureau of Reclamation 

to assess various storage alternatives. 

Introduction

The Bureau of Reclamation (Reclamation) is studying 

the benefits of additional water storage in the Yakima River 

Basin (Yakima River Basin Water Storage Feasibility Study 

or Storage Study) for agriculture, fish, and municipal uses. 

Long-term planning into the mid-21st century requires 

consideration of anticipated climate variability and change. 

Current hydrologic trends and global climate models indicate 

that the climate of the Pacific Northwest, a region that includes 

the Yakima River Basin, will be warmer than it is today by 

the mid-21st century and that streamflow patterns will change 

(Cayan and others, 2001; Mote, 2003; Stewart and others, 

2004). 

Effects of Potential Future Warming on Runoff in the 

Yakima River Basin, Washington 

By Mark C. Mastin 
2 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

The U.S. Geological Survey (USGS), in collaboration 

with Reclamation, developed a detailed set of watershed 

models (Mastin and Vaccaro, 2002) for non-irrigated areas of 

the basin under the Watershed and River Systems Management 

Program (WARSMP; U.S. Geological Survey, 1998). The 

watershed models have been linked to a Reclamationdeveloped water management model (RiverWare, Bureau of 

Reclamation, 2000) currently used for planning and operations 

in the Yakima River Basin. Reclamation requested that the 

USGS (L. Brekke, Bureau of Reclamation, written commun., 

July 2007) use these watershed models to simulate the 

sensitivities of runoff (streamflow) to potential future warming 

trends, relative to the current runoff characteristics for water 

years 1981–2005, referred to as the base period. 

Simple climate changes were imposed on the watershed 

models based on averaged results of global climate models 

for the Pacific Northwest compiled by the University of 

Washington Climate Impacts Group (CIG) (Mote and others, 

2003). The evaluation of the sensitivities of runoff for these 

particular climate changes was done by modifying the 

temperature-related watershed model parameters, running the 

modified model for the base period, and comparing simulated 

unregulated runoff to that simulated by the unaltered model. 

Purpose and Scope

This report documents the methods used to simulate 

changes in runoff from current conditions defined as 

the simulated runoff for the base period (water years 

1981–2005) to simulated runoff for two warming-trend 

scenarios. Simulated runoff was generated using a previously 

documented watershed model (Mastin and Vaccaro, 2002) 

for the Yakima River Basin. Two imposed climate scenarios 

representing warmer climates were simulated by adding 

1oC and then 2oC to the daily minimum and maximum air 

temperatures of the model input. The temperature increases 

varied monthly according to climate change studies modeled 

for the 2040s. The data will be used by Reclamation as 

input to its water-management model to simulate regulated 

runoff under future warming-trend scenarios. The results 

from RiverWare model simulations will be used in long-term 

planning of several proposed water-storage alternatives for the 

basin. 

Yakima River Basin Study Area

The Yakima River Basin drainage area is about 

6,200 mi2 and produces a mean annual unregulated runoff 

of about 5,600 ft3/s (about 4.1 million acre-ft, or 12.3 in.) 

and a regulated runoff of about 3,600 ft3/s (about 2.6 million 

acre-ft, or 7.9 in.) with reductions accounted for by 

irrigation diversions and return flows. The headwaters are 

on the humid east slope of the Cascade Range, where mean 

annual precipitation is more than 100 in. The basin ends at 

the confluence of the Yakima and Columbia Rivers in the 

low-lying, arid part of the basin that receives about 6 in. of 

precipitation per year. Most precipitation falls during the 

winter in the form of snow in the mountains. Mean annual 

precipitation for the entire basin is about 27 in. (about 

12,000 ft3/s, or 8.7 million acre-ft). The spatial pattern of 

precipitation resembles the pattern of the highly variable 

topography of the basin, which ranges in altitude from 400 to 

8,200 ft.

Agriculture is the primary economic activity in the 

basin. Average annual surface-water demand is about 

2.5 million acre-ft. Most demand is for the irrigation of 

about 500,000 acres in the low-lying semiarid to arid parts 

of the basin that, for the most part, is met by surface-water 

diversions. This demand is partially met by storage in five 

Reclamation reservoirs (Bumping, Cle Elum, Kachess, 

Keechelus, and Rimrock Lakes; fig. 1) that can store 

1.1 million acre-ft of water. 

Snow accumulation usually begins in late October or 

early November and ends by April. Snowmelt is critical 

for supplying runoff to fill reservoirs and to meet irrigation 

demands. The highest monthly runoff follows melting of the 

snowpack. The runoff volume during the irrigation season 

(generally April through August) closely relates to the volume 

of the snowpack on April 1. An example of this relation can 

be seen in a comparison of runoff for the American River near 

Nile, Washington, with April 1 snowpack (fig. 2). 
Introduction 3

WA19_0I80_Yakima-Maston_fig01-model units

121°

47°

47°

30'

46°

121°30' 120°30' 120° 119°30'

46°

30'

KITTITAS COUNTY

YAKIMA COUNTY

COUNTY

BENTON COUNTY

KLICKITAT

COUNTY

YAKIMA

Bumping

Lake

S Fk

N Fk

Cle Elum River

Bumping River

Ahtanum Creek

Tieton River Wenas Creek

North Fork

Dry Creek

Creek

Toppenish

RIVER

YAKIMA

Satus

Creek

Cle

Elum

Lake

Rimrock

Lake

Kachess Lake

Keechelus Lake

Teanaway River

Umtanum Creek

Little Naches River

Cowiche Creek

Cowiche Creek

River

Naches

RIVER

YAKIMA

RIVER

YAKIMA

American River

 COLUMBIA

 

RIVER

0 5 10 20 30 40 MILES

0 5 10 20 30 40 KILOMETERS

WASHINGTON

Yakima

River

Basin

Yakima

River

 Columbia

 River

EXPLANATION

Streamflow-gaging station

Meteorological site

Major reservoir

Basins simulated by watershed models

Naches Modeling Unit

Upper Yakima Modeling Unit

Yakima Canyon Modeling Unit

Satus/Toppenish Modeling Unit

Cascade Range

Base from U.S. Geological Survey digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Cle Elum

Parker

Wapato

Ellensburg

Umtanum

Kittitas Thrall

Toppenish

Moxee

City

Union

Gap

Yakima

Selah

Naches

Sunnyside

Richland

Kiona

Prosser

Grandview

Mabton

Satus

Zillah

Granger

Roza

Easton

Teanaway

Tieton Rimrock

Nile

Kennewick

Bumping

Ridge

Figure 1. Major reservoirs managed by the Bureau of Reclamation, meteorological and streamflow-gaging stations, and 

subbasins simulated by the four watershed models, Yakima River Basin, Washington.
4 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

Imposed Climate Changes

The climate changes considered here include changes in 

air temperature only, not changes in precipitation. The CIG 

(Mote and others, 1999, p. 36) determined that, “Projections of 

temperature changes, both globally and regionally, are made 

with higher confidence than precipitation changes.” Global 

climate models predict increases and decreases in precipitation 

for the Pacific Northwest. Due to this lack of consensus on 

future changes in precipitation, this study used precipitation 

values for the climate change scenarios that were the same as 

those measured for the base period. 

The CIG reviewed the results of eight global climate 

models available from the Intergovernmental Panel on 

Climate Change (IPCC), most were run for 1900–2100, and 

averaged the results for the Pacific Northwest region (Mote 

and others, 2003). Average temperature changes (compared to 

a control run that refers to 1990 measured temperatures) for 

the Pacific Northwest were 1.5oC warmer for the 2020s and 

2.3oC warmer for the 2040s. Reclamation determined that two 

global climate change scenarios would be simulated for the 

Yakima River Basin analysis: (1) average annual warming of 

1oC relative to the base climate period that represents early 

21st century conditions for the region (“plus one” scenario) 

and (2) average annual warming of 2oC relative to the base 

climate period (“plus two” scenario) that represents mid21st century conditions (L. Brekki, Bureau of Reclamation, 

Month

Air temperature scenario

Plus one 

(°C)

Plus two 

(°C)

Plus one 

(°F)

Plus two 

(°F)

January 1.05 2.11 1.89 3.80

February 1.15 2.30 2.07 4.14

March 1.17 2.34 2.11 4.21

April .85 1.69 1.53 3.04

May .53 1.06 .95 1.91

June 1.01 2.01 1.82 3.62

July 1.19 2.38 2.14 4.28

August 1.34 2.68 2.41 4.82

September .91 1.83 1.64 3.29

October .94 1.89 1.69 3.40

November .72 1.44 1.30 2.59

December 1.14 2.27 2.05 4.09

written commun., 2007). The Pacific Northwest is described in 

Mote and others (2003) as regionally coherent where “warm 

years tend to be warm, and cool years cool, everywere in the 

region.” For this reason, only regionally averaged change is 

considered and the temperature changes are assumed to be 

distributed uniformly across the basin.

Annual air temperature changes were divided into 

monthly changes based on seasonal changes projected for 

the Columbia River Basin based on IPPC Third Assessment 

Report models for the 2040s (Alan Hamlet, Climate Impact 

Group, University of Washington, written commun., 2007). 

Table 1 provides the monthly air temperature changes 

used in the watershed models to simulate the two climatechange scenarios. The watershed models operate in units of 

Fahrenheit, and therefore, both units are shown in table 1.

The evaluation of alternatives in Reclamation’s Storage 

Study are based on the water availability for irrigation and 

instream flows in the Yakima River Basin for water years 

1981–2005 (base period). The unregulated runoff simulated 

by the watershed models for the same period used the same 

parameters as those calibrated and tested for the WARSMP 

study (Mastin and Vaccaro, 2002), and was used as a basis to 

evaluate sensitivities to the climate change. 

Figure 2. Comparison of irrigation season (April 

through August) runoff at American River near Nile, 

and snow-water equivalent at Bumping Ridge on April 

1 for water years 1979, 1981, and 1984–2006, Yakima 

River Basin, Washington.

WA19-0180-Yakima-Maston_fig02-Linear Regression

0

50,000

100,000

150,000

200,000

250,000

0 10 20 30 40 50 60

SNOW-WATER EQUIVALENT, IN INCHES

RUNOFF FROM APRIL 1 THROUGH

AUGUST 31, IN ACRE-FEET

Linear Regression Line

Table 1. Monthly changes in air temperature for the plus one 

and plus two climate change scenarios used in the watershed 

model simulations, Yakima River Basin, Washington.

[Plus one and plus two scenarios represent an approximate 1 and 2°C, 

respective annual increase in air temperature from the base climate period. 

Abbreviations: °C, degrees Celsius; °F, degrees Fahrenheit]
Simulated Runoff Results 5

Watershed Models

Unregulated runoff in the Yakima River Basin was 

simulated for the warm-climate scenarios by the existing 

watershed models constructed using the Modular Modeling 

System (MMS; Leavesley and others, 1996) a component of 

WARSMP. Using a digital elevation model and a Geographic 

Information System (GIS) interface called the Weasel 

(Leavesley and others, 1997), four upland watershed models 

were delineated for the Yakima River Basin (fig. 1) upstream 

of the low-lying agricultural basins where streamflow 

diversions for irrigation and agricultural return flows begin. 

The modeled area in the basin accounts for more than 

95 percent of the total runoff generated within the entire basin. 

Within the four models, areas of similar hydrologic responses 

called model response units (MRUs) were delineated 

based on drainage pattern, precipitation, elevation, and soil 

characteristics; 1,110 MRUs in total were delineated for the 

four models. A complete discussion of the construction of 

the models is available in Mastin and Vaccaro (2002). The 

climate data input to the models include daily precipitation at 

26 sites, and daily minimum and maximum air temperature 

at 24 sites. A daily water balance was simulated at each 

MRU and runoff from surface, sub-surface, and ground-water 

sources was generated and accumulated at flow-routing nodes 

and used to simulate flow in channels. For the WARSMP, the 

models were calibrated to measured and estimated streamflow 

for water years 1950 through 1994 by adjustment of model 

parameters. The models were tested by holding the parameter 

values constant, running the model for 1995 through 1998, and 

comparing the simulated runoff with measured runoff. 

Air temperature was used in the watershed models to 

estimate potential evapotranspiration and solar radiation. 

The increased air temperature for the two warmer climate 

scenarios increased the potential evapotranspiration, and 

therefore, the actual evapotranspiration on each MRU over 

the base conditions scenario. Solar radiation that reaches 

the land surface was first estimated from a relation between 

recorded air temperature and cloudiness for a selected flat 

location and then adjusted for slope angle and orientation at 

each MRU. This relation uses the unadjusted recorded air 

temperatures, and therefore, the estimated solar radiation is the 

same for all scenarios. Estimated solar radiation was used in 

the calculations of potential evapotranspiration and the energy 

budget for snow simulation in the watershed models. 

The four WARSMP models were used to simulate runoff 

at selected flow-routing nodes for the base period (water 

years 1981–2005) for base conditions. Average runoff was 

calculated for each month and a mean monthly value was 

computed for the entire base period. Runoff for the plus one 

and plus two scenarios was simulated for the base period by 

changing the monthly adjustment parameters that represent 

the daily minimum temperature (tmin_adj) and the daily 

maximum temperature (tmax_adj) to reflect the expected air 

temperature changes shown in table 1. The model computes 

maximum air temperature for a particular MRU using all the 

valid maximum temperature inputs measured at a climate 

station inversely weighted by distance from the station to the 

MRU and adjusted using computed lapse rates. 

Three model simulations were made with each of the 

four watershed models and mean monthly runoff at all the 

flow-routing nodes were saved so they can be used as input of 

unregulated runoff for the RiverWare model. The mean runoff 

for each month and the annual runoff for the base period 

(water years 1981–2005) was then determined. The simulated 

changes in runoff are provided as percentages of change in 

monthly runoff; the percentages of change in runoff for the 

plus one and plus two scenarios from the base conditions 

simulated were computed from monthly and annual means 

computed for the base period. 

Simulated Runoff Results

This section focuses only on the results for a set of six 

selected sites because the same general pattern of change to 

runoff occurs at all model nodes. Results of runoff changes 

at six regulatory locations in the basin are shown in figure 3

and table 2. The locations include the points of inflow of 

five Reclamation-operated reservoirs in the basin (Bumping, 

Cle Elum, Kachess, Keechelus, and Rimrock Lakes) and one 

streamflow-gaging station that is monitored for regulating 

discharge on the lower Yakima River (Yakima River near 

Parker, fig. 1). The percentage of change in runoff for the 

plus one and plus two scenarios from the base conditions 

simulation, and the monthly and annual means computed for 

the period of simulation for 37 subbasins are presented in 

appendix A. These changes show the sensitivity of runoff to 

increased air temperature.
6 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

WA19-0180-Yakima-Maston_fig03-Discharge

0

200

400

600

800

0

2,000

4,000

6,000

8,000

10,000

12,000

0

200

400

600

800

1,000

1,200

Kachess Lake

Bumping Lake

RUNOFF, IN CUBIC FEET PER SECOND

Keechelus Lake

Cle Elum Lake

Yakima River near Parker

Rimrock Lake

0

200

400

600

0

200

400

600

800

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

Base Conditions

Plus One Scenario

Plus Two Scenario

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

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

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

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

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

Figure 3. Simulated mean monthly runoff for base conditions and plus one and plus two scenarios at selected sites in the 

Yakima River Basin, Washington.
Simulated Runoff Results 7

Site

Simulated change in mean monthly runoff (percent) Simulated 

change in mean 

annual runoff

(percent)

Maximum 

positive 

change

Month of

maximum change

Maximum 

negative 

change

Month of

maximum change

Plus one scenario

Yakima River near Parker 35.9 January -37.6 July -2.8

Bumping Lake 25.2 March -24.9 July -1.3

Cle Elum Lake 46.0 January -50.8 July -3.8

Kachess Lake 41.8 December -49.2 July -3.9

Keechelus Lake 47.6 January -49.9 July -3.7

Rimrock Lake 23.5 February -21.9 June -1.4

Plus two scenario

Yakima River near Parker 73.0 January -60.6 July -6.1

Bumping Lake 69.7 March -59.0 July -2.7

Cle Elum Lake 94.4 January -75.7 July -8.2

Kachess Lake 81.9 December -73.7 July -7.6

Keechelus Lake 93.1 January -71.3 July -7.5

Rimrock Lake 59.1 February -44.3 June -2.5

The change in mean monthly values for the plus one 

and plus two scenarios compared to base conditions ranged 

from about +48 to -51 percent for the plus one scenario 

and +94 to -76 percent for the plus two scenario (table 2). 

The maximum positive percentage deviations from the base 

conditions occurred during December to March and the 

maximum negative percentage deviations occurred during 

June and July. Mean annual changes for the warmer scenarios 

at the six selected sites were modest and all negative, ranging 

from -1.3 to -3.9 percent for the plus one scenario and -2.5 to 

-8.2 percent for the plus two scenario (table 2). A wider range 

of percent change was found for the entire list of stations 

in appendix A. Mean annual change ranged from +1.33 

to -12.85 percent with two thirds of the sites ranging from 

0.00 to -6.75 percent for the plus one scenario and 1.56 to 

-24.54 percent for the plus two scenario with two thirds of the 

sites ranging from -1.24 to -14.73 percent.

The general change in the runoff pattern for the two 

climate change scenarios is shown in hydrographs of 

monthly means for the three sets of simulations (fig. 3). 

November through March simulated runoff for the warmclimate scenarios was greater compared to base conditions 

because more autumn/winter precipitation was simulated as 

rain rather than snow. Most precipitation that falls as rain 

will runoff quickly, but precipitation that falls as snow will 

accumulate in the snowpack and may not become runoff 

until later in the season when air temperatures increase. 

Total simulated snowmelt for the base period was greater 

for all modeling units than the plus one and plus two climate 

scenarios (table 3). In a similar analysis for the Yakima River 

Basin using a 2oC warming scenario, a -59 percent change 

in the April 1 snowpack snow-water equivalent (SWE) was 

simulated relative to base condition (1950–2005) simulations 

(Mastin and Sharp, 2006). That same analysis simulated the 

greatest percentage change in the snowpack SWE at lower 

altitudes (less than 4,000 ft), but the greatest absolute change 

was in the 4,000–5,000-ft altitude zone. In this study, the 

smallest percentage of change in annual runoff was in the two 

highest altitude subbasins, Bumping Lake and Rimrock Lake 

subbasins (table 2). The small change in simulated runoff from 

the Rimrock Lake subbasin is partially explained by the fact 

that the subbasin contains glaciers that were simulated with 

a simple glacier-melt coefficient related to air temperature 

that does not change the volume of the glaciers. Spring and 

summer runoff in the Yakima River Basin depends on the 

snowpack to sustain flows, so as snowpack accumulation is 

less in spring due to warming trends, the simulated runoff 

during spring and summer decreases. Figure 3 shows the plus 

one and plus two hydrographs crossing the base condition 

hydrographs in April or May and remaining less than the baseconditions hydrograph through the remainder of the water 

year.

Table 2. Simulated changes in mean monthly runoff and mean annual runoff from the base condition for the plus one 

and plus two scenarios at selected sites in the Yakima River Basin, Washington.

[Plus one and plus two scenarios represent an approximate 1 and 2°C, respective annual increase in air temperature from the base climate 

period. Abbreviation: °C, degrees Celsius]
8 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

Summary

Monthly percentage differences in unregulated 

simulated runoff at points throughout the Yakima River 

Basin for potential future warming trends compared to base 

conditions of unregulated simulated runoff for water years 

1981 through 2005 were simulated using four previously 

calibrated watershed models. The watershed models were 

constructed and calibrated by the U.S. Geological Survey 

for the Watershed and River Systems Management Program 

(WARSMP). The simulated runoff for two different warmclimate scenarios will be used by the Bureau of Reclamation 

to adjust the unregulated runoff input to its water-management 

model of regulated runoff (RiverWare). The results from 

RiverWare model simulations will be used in long-term 

planning of several proposed water-storage alternatives for the 

basin. 

The sensitivity of the runoff in the Yakima River Basin to 

potential future warming trends was computed with two warmclimate scenarios that were simulated with a set of monthly air 

temperature increases applied to the time series of minimum 

and maximum daily recorded air temperature for water 

years 1981–2005. The monthly distribution of temperature 

increases were based on seasonal changes projected for the 

Columbia River Basin for the early and mid-21st century and 

averaged 1oC for the plus one scenario and 2oC for the plus 

two scenario. Based on work by the Climate Impacts Group at 

the University of Washington that averaged the results of eight 

global climate models for the Pacific Northwest, the Bureau of 

Reclamation determined that the 1 and 2oC annual temperature 

increases over the base period (water years 1981–2005) would 

be used as model scenarios because they represent reasonable 

estimates of global warming that can be expected by the 

early and mid-21st century respectively. Precipitation was not 

altered for the two warmer climate scenarios. 

Unregulated runoff was simulated at many of the flowrouting nodes in the watershed models for use as input to 

the RiverWare model. The same general pattern of increased 

runoff during late autumn and winter months and decreased 

runoff during late spring and summer months for the climate 

change scenarios from the base conditions is seen at all the 

nodes. Comparisons of the plus one and plus two scenarios to 

base conditions at six regulatory locations (five reservoirs and 

one river location) in the basin indicated that the maximum 

increases over the base conditions during the months of 

December to March varied from 24 to 48 percent for the plus 

one scenario and 59 to 94 percent for the plus two scenario. 

During late spring and summer months, simulations of the 

regional warming trends at these sites all were less than 

the base conditions with maximum changes that occurred 

in June and July, ranging from -22 to -51 percent for the 

plus one scenario and -44 to -76 percent for the plus two 

scenario. Annual differences at these sites ranged from -1.4 

to -3.9 percent for the plus one scenario and from -2.5 to 

-8.2 percent for the plus two scenario.

Modeling unit Area, 

in acres

Simulated snowmelt

Base condition Plus one Plus two

Inches KAF Inches KAF Inches KAF

Naches 708,543 566.5 33,449 511.7 30,213 435.7 25,726

Upper Yakima 721,638 806.7 48,512 703.8 42,324 575.9 34,633

Yakima Canyon 260,178 66.0 1,431 57.5 1,247 47.5 1,030

Satus/Toppenish 657,858 62.2 3,410 52.5 2,878 40.6 2,226

Total 2,348,217 86,802 76,662 63,615

Table 3. Simulated snowmelt for four watershed models for base conditions and plus one and 

plus two scenarios, water years 1981–2005, Yakima River Basin, Washington.

[Base condition: Simulated snowmelt for the base period (water years 1981-2005) using observed air 

temperatures. Plus one and plus two scenarios represent an approximate 1 and 2°C, respective annual increase in 

air temperature from the base climate period. KAF, thousand acre feet]
References Cited 9

References Cited

Bureau of Reclamation, 2000, RiverWare: U.S. Bureau of 

Reclamation Fact Sheet, accessed November 2007 at http://

www.usbr.gov/pmts/rivers/warsmp/riverware/index.html

Cayan, D.R., Kammerdiener, S.A., Dettinger, M.D., Caprio, 

J.M., and Peterson, D.H., 2001, Changes in the onset 

of spring in the western United States: Bulletin of the 

American Meteorological Society, v. 82, p. 399–415.

Leavesley, G.H., Restrepo, P.J., Markstrom, S.L., Dixon, M., 

and Stannard, L.G., 1996, The Modular Modeling System 

(MMS)—User’s Manual: U.S. Geological Survey Open-File 

Report 96-151, 142 p.

Leavesley, G.H., Viger, R.J., Markstrom, S.L., and 

Brewer, M.S., 1997, A modular approach to integrating 

environmental modeling and GIS: Proceedings of 15th

IMACS World Congress on Scientific Computation, 

Modelling, and Applied Mathematics, Berlin, Germany, 

August 24–29, 1997, 7 p.

Mastin, M.C., and Sharp, W., 2006, Comparison of simulated 

runoff in the Yakima River Basin, Washington, for present 

and global climate-change conditions: Proceedings of 

the Third Federal Interagency Hydrologic Modeling 

Conference, Reno, Nev., April 2–6, 2006.

Mastin, M.C., and Vaccaro, J.J., 2002, Watershed models for 

decision support in the Yakima River Basin, Washington: 

U.S. Geological Survey Open-File Report 02-404, 48 p.

Mote, P.W., 2003, Trends in temperature and precipitation 

in the Pacific Northwest during the twentieth century: 

Northwest Science, v. 77, no. 4, p. 271–278.

Mote, P.W., Holmberg, M., Mantua, N.J., and Climate Impacts 

Group, 1999, Impacts of climate variability: National 

Atmospheric and Oceanic Administration, Office of Global 

Programs, and JISAO/SMA Climate Impacts Group, 

Seattle, Washington, 110 p.

Mote, P.W., Parson, E.A., Hamlet, A.F., Keeton, W.S., 

Lettenmaier, D., Mantua N., Miles, E.L., Peterson, D.W., 

Peterson, D.L., Slaughter, R., and Snover, A.K., 2003, 

Preparing for climatic change—The water, salmon, and 

forests of the Pacific Northwest: Climatic Change, v. 61, 

no. 1 and 2, p. 45–88. 

Stewart, I.T., Cayan, D.R., and Dettinger, M.D., 2004, 

Changes in snowmelt runoff timing in western North 

America under a ‘Business as Usual’ climate change 

scenario: Climatic Change, v. 62, p. 217–232.

U.S. Geological Survey, 1998, Watershed and River Systems 

Management Program—Application to the Yakima 

River Basin, Washington: U.S. Geological Survey Fact 

Sheet 037-98, 4 p.
10 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

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Appendix A 11

Appendix A. Mean Monthly and Annual Unregulated Runoff Simulated for Base 

Conditions and Two Climate Change Scenarios, Plus One and Plus Two, for 

Indicated Subbasins

The percentage of change in runoff for the plus one and plus two scenarios from the base conditions simulation, and the 

monthly and annual means computed for the period of simulation for 37 subbasins are presented in appendix A in a spreadsheet 

in Microsoft© Excel. The appendix can be accessed and downloaded at URL http://pubs.usgs.gov/sir/2008/5124/sir20085124_

appendix.xls.
12 Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington

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Manuscript approved for publication, July 7, 2008

Prepared by the USGS Publishing Network 

Bob Crist

Bill Gibbs

Debra Grillo

Bobbie Jo Richey 

Sharon Wahlstrom

For more information concerning the research in this report, contact the 

Director, Washington Water Science Center

U.S. Geological Survey, 934 Broadway — Suite 300

Tacoma, Washington 98402

http://wa.water.usgs.gov
Mastin— Effects of Potential Future Warming on Runoff in the Yakima River Basin, Washington—Scientific Investigations Report 2008–5124