United States

Department of

Agriculture

Forest Service

Southeastern Forest

Experiment Station

Research Paper

SE-273

1988 Revisions to the

1978 National Fire-Danger

Rating System

Robert E. Burgan
November 1988

Southeastern Forest Experiment Station

P.O. Box 2680

Asheville, North Carolina 28802
Robert E. Burgan

Research Forester

Southern Forest Fire Laboratory

Macon, Georgia

Abstract.--The 1978 National Fire-Danger Rating System does not work well in

the humid environment of the Eastern United States. System modifications to

correct problems and their operational impact on System users are described.

A new set of 20 fuel models is defined and compared graphically with the 1978

fuel models. Technical documentation of System changes is provided.

Keywords: Fire potential, fire, wild-land fire, fuel, moisture, weather.

The 1978 National Fire-Danger Rating (NFDR) System (Deeming and others 1977)

has been used without modification since it was implemented. During the last

10 years some deficiencies in performance in the Eastern United States have

become apparent. These deficiencies were outlined at a National Fire-Danger

Rating Workshop held at Harper's Ferry, WV (Gale and others 1986). Workshop

participants included a cross section of researchers and State and Federal

users. The consensus was that research should find and implement solutions to

system shortcomings as quickly as possible. Accordingly, long-term research

issues were shelved, as were some management issues that were identified.

The research priorities addressed here were:

0 Improve the capability of the NFDRS to respond to drought in

humid environments.

e Provide system flexibility to reflect greening and curing of

live fuels.

. Correct the problem of overrating fire danger in the autumn.

0 Correct the problem of overrating fire danger after rainfall.

o Adjust the fuel models to better predict fire danger in humid

climates.
This publication describes the reasons these problems exist, and documents the

modifications made to correct them. Each problem and solution is described,

then operational impacts on users and System options are discussed. Fuel model

descriptions and technical documentation are provided in the Appendixes.

In revising the System, certain constraints were accepted:

* The revisions should be collapsible back to the original

(1978) NFDRS to minimize complications for western users, who

were not seeking System changes.

l The mechanism for reflecting drought should utilize a currently

available and relatively simple index that does not require

observation of new weather parameters.

l Basic research to develop a new live fuel moisture model could not

be performed in time to be used in this System revision.

l The revisions should expand user capabilities and user

responsibilities to influence the System.

In this paper, the version of the NFDRS implemented in 1978 is referred to

as the "1978 NFDRS." This revision of the 1978 NFDRS is referred to as the

ì1988 NFDRS." The 1978 NFDRS is fully documented (Bradshaw and others 1983),

so its technical concepts will not be repeated here.

The 1988 NFDRS revisions required development of a new set of 20 fuel

models, but the 20 fuel models developed for the 1978 NFDRS also remain

available for use. Selection of the 1978 fuel model set disables most of the

1988 NFDRS revisions, while selection of the 1988 fuel model set enables them.

PROBLMS AND SOLUTIONS

Response to Drought

The 1978 NFDRS relies largely upon l,OOO-hour timelag fuel moisture to

express the effects of normal annual drying and wetting cycles. This is

accomplished directly through the effect of changes in l,OOO-hour moisture on

Energy Release Component (ERC) and Burning Index (BI) calculations and

indirectly through the algorithm in which l,OOO-hour moisture is used to

calculate live herbaceous and woody fuel moistures. This concept works well in

relatively arid climates that have low minimum relative humidities, and limited

humidity recovery at night. However, in humid environments such as the Eastern

United States, the daily minimum relative humidity in summer is normally

greater than 40 percent, and the maximum at night is normally at least 80

percent. Such high humidities prevent the l,OOO-hour fuel moisture from

decreasing below about 15 percent, even during extended droughts. For example,

typical l,OOO-hour and live woody fuel moistures computed with the 1978 NFDRS

are compared in figure 1 for a dry environment in California and a humid

environment in Georgia. Even though 1986 was a severe drought year in Georgia,

the l,OOO-hour and live woody fuel moistures remained relatively high.

It is not suggested that the theory behind these calculations is incorrect;

in fact, the theory is supported by studies (Blackmarr and Flanner 1968;

Lindenmuth and Davis 1970; Reifsnyder 1961) showing that foliar moistures

typically attain lower values in arid than in humid environments. Therefore no

attempt was made to modify current theory; rather, a drought index (Keetch and

Byram 1968) was implemented in the 1988 NFDRS and used to modify the amount of

dead fuel available for consumption.

2
250 ,

I

I

O" lJAN lFEBlMARlAPRlMAYlJUNlJUL lAUGlSEPlOCTlNOVlDECi

Figure 1. --l.OOO-hour timelag (above) and live woody fuel moisture (below) corparisons

for a relatively dry western environment (Stonyford Ranger Station in California) and

a humid eastern environment (Athens, GA) in 1986. A generally high relative humidity

prevents low l.OOO-hour fuel moistures in the humid environment.

+

14 -

‘:.*a

X.

:*-. . . . . . . .

07 -

a......

* . . . . . . . . . , . . . . . . .

. . . . . . .._..............

O" JAN IFEBIMARIAPRIMAYIJUNIJUL IAUGISEPIOCTINOVIDEC~

3
The Keetch-Byram Drought Index (KBDI) is well known in the Southeastern

United States and has also been used to some extent in the Northeast. Its

purpose is to estimate deep drying of litter and duff. It is assumed that, as

deep drying occurs, additional fuel becomes available for consumption within

the flaming front of a fire.

The 1978 NFDR fuel models had no reservoir of additional fuel that could be

used to simulate increased fuel availability as drought progressed. Therefore,

they were modified to include a potential dead fuel load that can be added to

the fuel model as a function of the KBDI. The functional relationship is shown

in figure 2. The total dead load increases above a threshold KBDI value of

100, which signals that drought has progressed beyond the "zero or incipient"

stage (Keetch and Byram 1968). Tbe added fuel is distributed in proportion to

the predrought dead fuel loads, with depth increased to preserve the packing

ratio. The total potential dead load increase is not realized until the KBDI

reaches 800.

Figure 3 presents the KBDI at Athens, GA, for 1986, and the lo-hour timelag

fuel load to illustrate the adding of dead fuel to the model when the KBDI

exceeds 100. The concept of drought adding available fuel is similarly

extended to other dead fuel classes in a fuel model.

Although this added drought response capability was developed to alleviate

eastern problems with the 1978 NFDRS, it could also prove helpful in the

Western United States. It can be disabled by selecting the 1978 NFDRS fuel

set however.

0

I I I I I I I I

0 100 alo so0 400 !500 600 700 800

KEXTCH-BYRAM DROUGHT INDEX

Figure 2.--Functional relationship of fuel load addition due to drought. as defined by

the Keetch-Byrar Drought Index.
800

720

640

560

480

400

320

240

160

8 0

T

PI

O" JAN IFEBiMARIAPR1MAYIJUNlJUL IAUGISEP

1.6

4 :::

2g 1.0

fit 0.8

i! 0.6

0.4

0.2

T

Figure 3.--h the Keetch-Byrar Drought Index fluctuates above 100 (above), lo-hour

fuel loading in the 1988 NPDRS changes. while that for the 1978 NPDRS is constant

(below). Values are for 1986 in Athens, GA (model C).

'*' JAN lFEBIMARlAPRIMAYiJUNlJUL lAUGk3EPlOCTlNOVlDEC

5
Greening and Curing Flexibility

Fundamental changes in the 1978 NFDRS model for live fuel moisture (Burgan

1979) may be required. Because it was obvious such changes could not be

implemented in time for this effort, they are left for future research.

In the 1978 NFDRS, users of the AFFIRMS System (Helfman and others 1980)

could signal the start of greening at any time. Whereas the simulated greening

process was relatively gradual, the time over which it was assumed to occur was

fixed by the climate class assigned to the weather station, and automatically

controlled by AFFIRMS.

Curing in the autumn was not assumed to be gradual. The user could simulate

the autumn transition from summer to winter only by entering an AFFIRMS command

to indicate that vegetation had frozen. The change in calculated moistures of

live herbaceous and woody fuels to dormant-season values was instantaneous.

The actual fall curing process is gradual.

Differences between the AFFIRMS System, used for current daily operation of

the 1978 NFDRS, and the FIRDAT program of FIREFAMILY (Main and others Ig82),

used for historical data analysis, caused another problem. Historical analyses

of fire danger produced by FIRDAT did not use greening and curing dates entered

by the AFFIRMS user. The.historical fire-danger profile often differed from

conditions during a particular fire season, and fire planning was adversely

affected.

The 1988 NFDRS requires users to enter greenness factors that express actual

greening and curing of both live herbaceous and live woody vegetation.

Greenness factors values are entered separately for live herbaceous and woody

vegetation and included as part of each day's weather record. This feature

permits the user to control each greenness factor independently, and inclusion

of greenness factors in the daily weather record solves the problem of matching

historical fire-danger profiles with the actual conditions.

Greenness factors represent your visual estimate of the current general

greenness of herbs and grasses, and shrubs, compared with their maximum

greenness. The greenness factors range from 0 to 20, where 0 represents fully

cured herbaceous plants or dormant shrubs, and 20 represents a condition in

which the herbs and/or shrubs are as green as they ever get. Intermediate

values represent intermediate greenness. A factor of 10 indicates that the

herbs or shrubs are about half as green as they ever get. The greenness

factors are independent of climate class; that is, they range from 0 to 20 for

all climate classes.

As the herbs and shrubs green in the spring, increasingly larger greenness

factors are entered for each. Because herbs and grasses may green at different

times or rates than shrubs, the herbaceous and live woody greenness factors do

not have to be the same. In addition, it is not necessary to increase the

greenness factors by one each day. If greening is proceeding slowly, the same

values may be entered for several days. If greening is rapid, the greenness

factors may be increased more than one per day. The curing process is handled

similarly. That is, the greenness factors for herbs and shrubs are decreased

gradually as curing progresses.

The greenness factors for herbs and shrubs also provide a mechanism for

reflecting the effect of summer droughts. If a drought becomes so severe that

herbs and grasses begin to cure and shrub leaves wilt, the herb and live woody

6
The difference in fall curing can also be seen. The 1978 NFDRS decreased the

live woody moisture to the dormant period minimum of 70 percent for climate

class 3, on the day a freeze occurred. But with the 1988 NFDRS, the live woody

fuel moisture was gradually decreased to this value as the user slowly reduced

the live woody greenness factor to 0.

250

225

200

175

T

i

greenness factors can be reduced appropriately. If the drought is later

broken, the greenness factors can be increased again to reflect increased

moisture. However, the user should make such changes gradually to reflect what

is actually occurring in the fuel type.

The user must determine the greenness factors to enter for herbs and

shrubs. This is an example of added system flexibility resulting in added user

responsibility. Greenness factors must be entered by all system users,

regardless of whether they use the 1978 or the 1988 NFDRS fuel model set.

Guidelines for adjusting greenness factors are provided in the section titled

"Operational Considerations."

Figure 4 illustrates the effect of varying the woody greenness factor. In

this figure, live woody (shrub) moisture calculated with the 1978 NFDRS is

compared with calculated values from the 1988 NFDRS. Greening was started at

the same time in each case. The 1988 NFDRS strongly reflects the effect of

summer drying on live woody moistures. This effect was produced by reducing

the live woody greenness factor during the dry periods, then increasing it

after significant precipitation occurred.

50 - winter summer Fall

4

I

25 - Gmennen Factor

O" JAN IFEBIMARIAPRIMAYIJUNIJUL lAUGbEPIOCTlNOVh.lEC

Figure &.--An example of improved capability to calculate reduced live fuel moisture

through use of reduced greewxess factor values in the 1988 NPDRS. as compared with

live fuel moisture calculations from the 1978 NPDRS. The Y-axis scale references both

percent moisture and greenness factor. Values are for 1986 in Athens. GA.
errating Fire Danger in the Autumn

A primary reason the 1978 NFDRS overrated autumn fire danger is its poor

ability to simulate fall curing. Herbs and shrubs may cure at different times,

and the shrubs may be deciduous. Neither of these circumstances can be

recognized within the 1978 NFDRS; the vegetation is assumed to cure immediately

when a freeze occurs. The result of this assumption is an instantaneous

increase in fire danger, due to the sudden reduction of live fuel moistures to

their dormant season minimums. The greenness factors in the 1988 NFDRS permit

simulation of gradual fall curing, resulting in a gradual increase of autumn

fire danger.

In addition, the live woody fuel load can be defined as deciduous or

evergreen. Deciduous models allow simulation of leaf fall by permitting load

transfers between the live woody class and the fine dead fuel class as a

function of the greenness factor for live woody vegetation. This is an

extension of the concept in the 1978 NFDRS that live herbaceous fuel load can

be transferred between the live and dead categories. When the live woody

greenness factor is 0, all the live woody load is transferred to the fine dead

fuel class. When it is 20, the live woody load is at its full assigned value

for the fuel model, and the fine dead fuel load is correspondingly reduced.

Figure 5 illustrates the difference between fuel loading profiles for the

1978 NFDRS and the 1988 NFDRS with the deciduous option selected. The live

woody load is constant at 0.5 ton per acre for the 1978 NFDRS model C, while it

fluctuates from 0.0 to its maximum value of 0.8 ton per acre for the revised

model C. These load changes occur as the live woody greenness factor is

changed during the year.

The 1988 System transfers fuel from the live woody and herbaceous classes,

as well as the drought fuel class, into the fine dead class during a summer dry

period. By comparison, the 1978 NFDRS shows only a slight transfer of fuel

into the fine dead fuel class during summer for two reasons: (1) the live woody

load is held constant, and (2) high calculated herbaceous moistures permitted

little herbaceous load transfer into the fine dead fuel class during the

July-August dry period.

The 1988 NFDRS offers the capability to select between an evergreen and a

deciduous live woody fuel load. The evergreen mode should be selected if the

live shrubs are not deciduous, or if you do not want to permit this fuel load

transfer for some other reason. Selection of the 1978 NFDRS fuel model set

eliminates the option of indicating whether or not the live woody vegetation is

deciduous.

Overrating Fire Danger After Rainfall

The 1978 NFDRS can overrate fire danger after rainfall, especially if strong

winds or low humidities occur after a frontal passage. The Spread Component

(SC), Ignition Component, and Burning Index rise rapidly with increasing

windspeed, and low calculated fine dead fuel moistures associated with low

relative humidity. Fine dead fuels are defined as any dead plant material less

than one-fourth inch thick.

If fuel moisture sticks are not used, fine dead fuel moisture calculation in

the 1978 NFDRS is unaffected by precipitation, unless it is occurring at

observation time. If lo-hour timelag fuel moisture sticks are used, they

provide a 20-percent influence on the fine dead fuel moisture. The remainder

8
1.0

0.9

0.8

2 0.7

$ 0.6

b 0.5

:

g o-4

i.2 0.3

0.2

0.1

0.0

I

. .

IJ'AN IFEBIMARlAPR1MAYlJUNlJUL lAUGbEPIOCTlNOVlDEC

Figure 5.--Live woody (above) and fine dead (below) fuel load profiles from model C

for the 1978 NPDRS and the 1988 NPDRS during a drought year (1986) in Athens, GA. The

live woody load was declared deciduous.

3.0

2.7

2.4

J

1988 NFDF&s

f j 2.1 -

% 1.8-

t

1.5 - 1978 NmRa

0.6 -

-1

x......................+ _.... ..-“.*.‘. ._..,....(

0.3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

"' IJAN lFEBIMARlAPRIMAYIJUNIJUL lAUGbEPIOCTlNOVlDEC

9
1988 NFDRS option of fine fuel moisture set

equal to measured fuel stick mosture

05

0 0

19’78 NFDRS calculated fine fuel moisture

1

IJAN IFEBIMARlAPRIMAYIJUNlJUL lAUG&XPIOCTINOVIDEC

Figure 6.--Differences between fine-fuel moisture determined by weighing fuel sticks

and Pine-fuel moisture estimated by the 1978 NPDRS (above) and the 1988 NPDRS

(below). Values are for 1986 in Athens, GA.

1988 NFDRS option of fine fuel moisture set

qua1 to measured fuel stick moisture

Fine fuel moisture calculated bv the 1988 NFDRS when

O”

‘measured fuel stick moistures are unavailable

JAN IFEB IMAR~APR IMAY IJUN IJUL IAUGISEP IOCT

1 0
of the calculation is a function of current dry-bulb temperature and relative

humidity. Experience has shown that both methods produce fine dead fuel

moisture values that are too low. In addition, recent research (Anderson 1985)

has shown that few fine dead fuels actually have a l-hour timelag as has been

thought in the past. Rather, their response time, while variable, is closer to

10 hours.

The 1988 NFDRS provides an option to set the fine dead fuel moisture equal

to the lo-hour timelag fuel stick moisture. The effect of choosing this option

is shown in figure 6. In general, this revision produces higher fine dead fuel

moistures and much more response to rainfall events. Whether or not this

option is selected, use of fuel moisture sticks and entry of measured values is

strongly recommended. When fuel moisture sticks are not used in the 1988 NFDRS,

the fine dead fuel moisture is calculated as a function of loo-hour timelag

fuel moisture, and observed dry-bulb temperature and relative humidity. Use of

the loo-hour timelag fuel moisture provides a mechanism for including the

effect of precipitation events that do not occur at observation time.

If the user chooses the 1988 NFDRS fuel models but does not want to set fine

dead fuel moisture equal to lo-hour timelag fuel moisture, the 1988 NFDRS still

does so on the day of and day following a precipitation event of more than 0.1

inch to reduce the problem of overrating fire danger after rain. Otherwise the

fine dead fuel moisture calculation is not affected.

Fire danger can also be overrated after a rain if strong winds persist after

frontal passage. The 1978 NFDRS uses an adjustment factor that depends on the

fuel model to reduce windspeeds measured at the standard height of 20 feet

above surrounding vegetation to midflame level. Subsequent research (Albini

and Baughman 1979) indicates that wind adjustment factors for closed stands

such as hardwood or hardwood/conifer forests in the East should be about 0.2

during the summer and about 0.5 during the winter. The 1988 NFDRS revision

provides a variable windspeed adjustment factor for fuel types that have

deciduous live woody fuel. The windspeed is reduced most during the summer OT

whenever the shrubs are fully green, least when the shrubs have lost their

leaves, and an intermediate amount at intermediate greenness levels. These

conditions are indicated by user entry of a greenness factor for live woody

fuels. The windspeed adjustment factor remains constant for fuel models whose

live woody fuel load is declared evergreen (nondeciduous) or for models that do

not have a live woody fuel load.

The 1988 field tests indicated that with only the above revisions fire

danger was still often overrated on the day of and day following

precipitation. Therefore, the wind adjustment factor is now multiplied by 0.3

on those two days only. This correction reduces the sensitivity of the 1988

NFDRS to wind until the dead fuels have had at least 1 day of drying.

Figure 7 illustrates the effect of this change for fuel model C. Choice of

the 1978 NFDRS fuel models eliminates the above-described changes to the

windspeed adjustment factor.

1 1
08

2s

3 07

8 06

55

g 05

W

2 04

g 03

02

?lAPRIMAYlJUN

Figure ‘J.--For sole fuel models. the variable wind adjustment factor of the 1988 NPDRS

tends to produce higher windspeeds than the 1978 NPDRS during the winter and lower

windspeeds in the summer. Values are from model C for 1986 in Athens, GA.

Revised Fuel Models

The changes described required modification of all 20 I.978 NFDRS fuel

models. A second set of 20 fuel models was created. In some cases, fuel loads

were changed to improve the seasonal response, but the major changes involved

adding a minimum and maximum wind adjustment factor and a reservoir of dead

fuel to improve the drought response. The user can choose which set of fuel

models to use: the original 1978 NFDRS models or the 1988 revision of those

models. Both the 1978 and 1988 NFDRS fuel models are listed in appendix A. As

noted previously, the fuel model set chosen determines whether the system

revisions are implemented.

System Response Comparison

SC, RRC, and BI profiles for the 1986 fire season at Athens, GA (fig. 8)

illustrate the combined effects of the revisions. Values of SC are reduced

during the January-April dormant season, but slightly increasededuring a

midsummer and early fall drought. For this example, fine dead fuel moisture

was set equal to the measured fuel stick moisture. This usually results in

higher fine dead fuel moisture values than are obtained through the standard

1978 NFDRS calculations. Because the SC is strongly affected by fine dead fuel

moisture, the effect is to produce a general reduction in SC throughout the

year, with the effect being greatest during the cool, moist period of winter

and early spring. During the May-June period, the 1988 system SC is near 0 for

the additional reason that the 20-foot windspeeds undergo their greatest

adjustment to midflame level windspeeds when the vegetation is in full leaf. A

small effect of drought on the SC can be seen during the July-August and

October periods when deep drying increased the amount of available fuel.

12
The RRC (fig. 8) is slightly higher for the 1988 NFDRS than for the 1978

NFDRS during the spring because the live woody load was designated to be

deciduous, and was thus transferred to the fine dead fuel class during the

dormant season. The most dramatic difference, however, occurs during the

summer drought, when the RRC is significantly increased for the 1988 System.

This increase reflects a combination of both increased dead fuel load due to

deep drying, and coincidental reduction of live fuel moistures, simulated

through reduction of greenness factors to help reflect the severity of the

drought. Greenness factors were added to the historical weather data for the

Stonyford, CA, and Athens, GA, weather stations, after consultation with local

fire managers. The FIREFAMILY programs have been restructured to use greenness

factors as they become available in new weather records, or to process older

data without them.

The BI (fig. 8) is a function of both the ERC and the SC. Thus, it is most

effective in illustrating the combined effects of all the System revisions.

Winter and early spring BI values are reduced primarily by letting fine dead

fuel moisture equal measured fuel stick moisture. Summer drought is better

reflected through a combination of increasing dead fuel availability and

reducing live fuel moisture. The fire danger increases slower in late November

and December, as a result of a more gradual simulation of the fall curing

process.

OPERATIONAL CONSIDERATIONS

Impacts on All Users

The revisions to the 1978 NFDRS have been structured to enable fire managers

to use the System nearly unchanged or to select those modifications that

address specific local problems. The exceptions are mandatory entry of

greenness factors for live herbaceous and woody fuels, and addition of the

KBDI. First, let us consider the impacts this revision will have on all users

of the NFDRS.

The KBDI computation requires entry of average annual precipitation amount at

your weather station to the station catalog. This includes both rainfall and

the water equivalent of snowfall. If you do not take weather all year, or do

not know what this value is, a reliable estimate can be obtained from the

nearest National Weather Service Office. The KBDI computation also requires

daily entries of precipitation amount.

At the beginning of the fire season, you need to enter a starting KBDI

value. Normally, this value would be near 0 because winter rainfall or snow

melt have recharged soil moisture. However, this inquiry provides an

opportunity to enter an estimated value if significant drying occurs before you

activate the weather station and begin calculating the KBDI. In such

instances, use table 1 to make your best estimate. It indicates the number of

rainless days to reach KBDI values of 100, 200, 300, or 400 for various mean

annual precipitation amounts and at various average maximum daily dry-bulb

temperatures. Obviously, this table can only serve as a rough guide to a

reasonable starting KBDI value. It is preferable to begin calculations after a

significantly wet period, when soils are fully charged with moisture.

13
1 4

27 :

:

:

Pfgure 8.--Cumulative effects of the 1988 NPDRS revisions on Spread Component (top),

Energy Release Component (middle). and Burning Index (bottom). for the 1.978 NPDRS and

the revised NPDRS. Values are from model C ior 1986 in Athens, GA.

40

36

32

28

24

20

16

12

08

04

0 0

T
Table 1. --Rainless days required to reach various KBDI values

Mean

Average daily maximum dry-bulb temperature

60 OF 70 OF 80 OF

annual

precip. KBDI KBDI KBDI

(inches) 100 200 300 400 100 200 300 400 100 200 300 400

1 0 100

15 100

20 100

2 5 6 1

z; ;i

40 4 1

4 5

;;

;::

27

60 25

6 5 2 3

20

20

19

200

200

200

161

105

100

g

60

54

i;

43

40

300

300

300

261

205

160

141

125

112

:z$

6 5

400

400

400

361

305

260

215

175

162

145

131

118

107

102

97

4’;

34

32

25

2 1

19

1 7

15

13

1 2

1 1

1 0

;

loo 189 289 27 60 95

99 149 238 23 48 8 1

7 7 127 177 20 4 1 6 6

6 5

452 1;;76 110 y; ;;12

3 5 56

25 29 41 47

40 6 5 97 lo 22 3 5

3 5 5 7 8 4 ii 19 3 0

3 1 5 0 7 4 1 7 27

28 45 66 24

2 5 4 1 59

ii :;

22

23 3 7 5 4 6 1 2 20

2 1 3 4 5 0 6 11 1 8

20 3 2 4 7 ; 1 1 1 7

19 3 0 4 4 lo 1 6

145

1182

;9”

z:;‘53 2

29

2 7

25

2 4

Use of greenness factors requires entry of the season of year as part of the

daily weather record. This may seem a trite entry, but proper implementation

of the greenness factors was impossible without it. The following tabulation

provides guidelines for both season and greenness factor entries.

Season Guideline

Winter Enter winter only when herbs are cured; and

shrubs are dormant. Enter both herb and woody

greenness factors as 0 (zero).

Spring Enter spring from the time either the herbs or

shrubs first begin a new season's growth until

the herbs complete their spring growth flush. If

the shrubs begin to green but the herbs are still

cured, continue to enter a greenness factor of 0

for the herbs until they too begin to green, then

start increasing it. Gradually increase the

live woody greenness factor as the shrub growth

flush increases. Follow similar reasoning if the

herbs and grasses green before the shrubs.

Summer Enter summer from the time the herb growth flush

is completed until the shrubs begin to show signs

of fall curing. Enter separate values that

represent the relative greenness of herbs and

shrubs. Often herbs cure during the summer,

while shrubs remain quite green. In this case,

the herb greenness factor should be reduced to 0,

while the woody greenness factor remains at some

value intermediate between 1 and 20.

1 5
Fall Enter fall from the time deciduous shrubs begin

to lose their leaves, or evergreen shrubs begin

to enter dormancy, until the shrubs and herbs

are fully dormant. As fall progresses, gradually

reduce the greenness factors for grasses and

shrubs if either. is above 0. If grasses are

cured, enter the herb greenness factor as 0.

When grasses are cured and shrubs are dormant,

enter a greenness factor of 0 for both, and cycle

the season entry back to winter.

When entering live herbaceous and woody greenness factors, it is important

to avoid large changes. It is reasonable to increase or decrease the greenness

factors gradually, or to hold them constant for a number of days, but you

should not vacillate between increasing and decreasing values over short time

periods. Basically, the values should be 0 in the winter and increase from 1

to 20 in the spring. Then, during dry periods, as plants begin to show signs

of moisture stress, decrease the herbaceous greenness factor to help reflect

obvious curing of grasses or other herbaceous plants, especially annuals. For

perennials and shrubs that may not show immediate obvious signs of drying, the

following guideline is adapted from work by Johnson (1980) for the Southeastern

United States. It is just a guideline and is no substitute for common sense or

visual observation of what is actually occurring in the field. With experience,

you may want to revise the guideline for your location.

Suggested Greenness Factors During Dry Periods

KBDI value Greenness factor

O-200

201-220

221-240

241-260

261-280

281-300

;%;t:

341-360

20

19

18

17

16

15

14

13

12

1 1

1 0

KBDI value Greenness factor

401-420

4.x-440

441-460

461-480

481-500

501-520

521-540

541-560

:::-580 +

If the KBDI drops suddenly due to significant rainfall, increase the

greenness factor gradually, rather than jumping it to a higher value just to

follow the above guideline. The vegetation is not likely to green

significantly in 1 day.

1 6
User Options

The mechanics of new selections in the 1988 NFDRS are provided in revised

users manuals for the AFFIRMS, FIREFAMILY, and personal computer NFDRS

(Donaldson 1988) programs, or in specific prompts presented during program

operation.

Your first choice is between the 1978 and the 1988 NFDRS fuel models. Your

selection should be based on whether the 1978 fuel models have served you well

in the past. Remember that if you select the 1978 NFDRS fuel models, you still

need to enter greenness factors, season, and precipitation amount in your daily

weather record. The KBDI will be provided regardless of your choice. If you

select the 1988 fuel models, you will need to reanalyze your historical weather

data and redefine your manning class breakpoints. Obviously, the 1988 fuel

models are going to produce different seasonal fire-danger profiles.

If you use the 1988 NFDRS fuel models, your second choice is whether or not

to set the fine dead fuel moisture equal to the observed lo-hour timelag fuel

stick moisture. If this option is selected, the fine dead fuel moisture will

always equal the lo-hour timelag fuel moisture. If it is not selected, fine

dead fuel moisture will equal the lo-hour fuel moisture only on the day of and

the day after precipitation. In general, if your fine dead fuels are composed

primarily of conifer needles and/or hardwood leaves that have a waxy surface

when fresh, select this option. But if your fine fuels are composed primarily

of grasses, lichens or other very small nonwaxy fuel particles, do not select

this option. Before making this decision, consider whether the 1978 NFDRS has

been overrating fire danger in the past.

The last choice is whether or not to define the live woody vegetation as

deciduous or evergreen. Broadleaf shrubs that do not lose their leaves are

defined as evergreen.

Users who want to minimize the effect of the 1988 NFDRS revisions should:

. Select the 1978 NFDRS fuel models.

l Do not set fine dead fuel moisture equal to lo-hour fuel stick moisture.

l Enter live woody and herbaceous greenness factors as follows:

l Increase both live herbaceous and woody greenness factors

from 0 to 20 during spring greening period (7, 14, 21 or 28

days for climate classes 1, 2, 3, or 4, respectively).

l Enter the live herbaceous greenness factor as 20 until the

calculated herbaceous moisture decreases below 30 percent, or

a killing frost occurs, then begin entering 0.

l Keep entering the live woody greenness factor as 20 until a

killing frost occurs, then begin entering 0.

l Enter 0 for both greenness factors when the grass is cured and

the shrubs are dormant.

Your selection of options provided with the 1988 NFDRS can make a

significant difference in the seasonal fire-danger profile, depending on the

fuel model used. You are encouraged to use the FIRDAT program of FIREFAMILY to

examine the effects of different choices for dry, wet, and average fire

seasons before making your decisions.

17
Field personnel at the Harpers Ferry NFDRS Workshop asked that the utility

of the 1978 NFDRS be improved for the humid environment of the Eastern United

States and that the modifications be made as soon as possible. Users in the

Western United States did not ask for System changes. The revisions described

here have been structured to minimize impacts on western users, while

permitting modifications that solve eastern problems.

Field testing at several locations in the Eastern United States, California,

and Alaska has shown that these revisions effectively deal with the concerns of

the eastern users. It must be remembered, however, the NFDRS absolutely

requires proper weather station location and maintenance, as well as consistent

and accurate observations and data entries. Without strong, competent field

support, the National Fire-Danger Rating System can never be expected to

produce useful results.

1 8
Albini, F.A.; Baugbman, R.G. 1979. Estimating windspeeds for predicting

wildland fire behavior. Res. Pap. INT-221. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Forest and Range Experiment

Station. 12 pp.

Anderson, H.E. 1985. Moisture and fine foregg fuel response. In: Donoghue,

L.R.; Martin, R.E., eds. Proceedings, 8 conference of fire and forest

meteorology: 1985 April 29-May 2; Detroit, MI. Bethesda, MD: Society of

American Foresters: 192-199.

Blackmarr, W-H.; Flanner, William B. 1968. Seasonal and diurnal variation in

moisture content of six species of pocosin shrubs. Res. Pap. SE-33.

Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern

Forest Experiment Station. 11 pp.

Bradshaw, Larry S.; Ikeming, John E.; Burgan, Robert E.; Cohen, Jack D., camps.

1984. The 1978 National Fire-Danger Rating System: Technical Documentation.

' Gen. Tech. Rep. IN?'-169. Ogden,UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station. 44 pp.

Burgan, Robert E. 1979. Estimating live fuel moisture for the 1978 National

Fire-Danger Rating System. Res. Pap. m-226. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Forest and Range Experiment

Station. 17 pp.

Deeming, John E.; Burgan, Robert E.; Cohen, Jack D. 1977. The National

Fire-Danger Rating System-1978. Gen. Tech. Rep. INT-39. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest and Range

Experiment Station. 63 pp.

Donaldson. Bryan G. The National Fire-Danger Rating System on a personal

computer. U.S. Department of Agriculture, Forest Service, Southeastern

Forest Experiment Station, Southern Forest Fire Laboratory, Macon, GA. [In

preparation.]

Gale, Robert; Eubanks, Roger; Roussopoulos, Peter., camps. 1986. NFDRS-East

Workshop; 1986 May 12-15; Harper's Ferry, WV. On file with: U.S. Department

of Agriculture, Forest Service, Forest Fire and Atmospheric Sciences

Research, P.O. Box 2417, Washington, D.C. 20013. 31 pp.

Helfman, Robert S.; Straub, Robert J.; Deeming, John E. 1980. User's guide to

AFFIRMS: time-share computerized processing for fire danger rating. Gen.

Tech. Rep. m-82. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station. 150 pp.

Johnson, Von. 1980. Letter dated July 16 to James Turner, Jr. On file with:

U.S. Department of Agriculture, Forest Service, Southeastern Forest

Experiment Station, Southern Forest Fire Laboratory, Rt l., Box 182A, Dry

Branch, GA 31020.

1 9
Keetch, John J.; Byraa~, George M. 1968. A drought index for forest fire

control. Res. Pap. ~~-38. Asheville, NC: U.S. Department of Agriculture,

Forest Service, Southeastern Forest Experiment Station. 32 pp.

Lindenmuth, A.W., Jr.: Davis, James R. 1970. Foliar moisture content of

chaparral in Arizona: accounting for its variation and relating it to

prescribed fires. Res. Note ~~-158. Fort Collins, CO: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment

Station. 8 pp.

Main, William A.; Straub, Robert J.; Paananen, Donna M. 1982. FIREFAMILY: fire

planning with historic weather data. Gen. Tech. Rep. NC-73. St. Paul, MN:

U.S. Department of Agriculture, Forest Service, North Cent-al Forest

Experiment Station. 31 pp.

Reifsnyder, William E. 1961. Seasonal variation in the moisture content of

green leaves of mountain laurel. Forest Science. 7(1):16-22.

20
APPENDIX A: FUEL MODEL DESCRIPTIONS AND SEASONAL PROFILES

1978 NFDRS Fuel Model Descriptions

Fuel model

Fuel model

parameters A B C D E P G H I J K L N 0 P Q* R s T u

Load (tons/acre)

l-hour dead 0.2 3.5 0.4

lo-hour dead - - 4.0 1.0

loo-hour dead - - 0.5 - -

1000-hour dead - - - - - -

Woody - - 11.5 0.5

Herbaceous 0.3 - - 0.8

Surface-area-to-volume ratio (l/ft)

l-hour dead 3,ooo 700 2,000

lo-hour dead - - 109 109

100-hour dead - - 30 30

lOOO-hour dead - - 8 - -

2.0 1.5

1.0 0.5

-- 0.25

-- --

3.0 0.5

0.75 0.5

1,250 2,000

109 109

-- 30

-- --

2.5 2.5 1.5 12.0

2.0 2.0 1.0 12.0

1.5 5.0 2.0 10.0

- - 12.0 2.0 12.0

9.0 0.5 0.5 --

-- 0.5 0.5 --

700 2.000 2,000

109 109 109

30 30 30

-- 8 8

Woody - - 1,250 1,500 1,500 1.500 1,250 1.500 1,500

Herbaceous 3,000 - - 2,500 1.500 2.000 - - 2,000 2,000

Heat content (all fuels)

1.500 1,500

IO9 109

30 30

8 8

-- --

-- --

7.0 2.5 0.25

7.0 2.5 --

6.0 2.0 --

5.5 2.5 --

-- -- --

-- -- 0.5

1.5 2.0 1.0 2.0 0.5 0.5 1.0 1.5

1.5 3.0 1.0 2.5 a.5 0.5 0.5 1.5

-- 3.0 0.5 2.0 o-5 0.5 -- 1.0

-- 2.0 - - 1.0 -- 0.5 -- - -

2.0 7.0 0.5 4.0 0.5 0.5 2.5 0.5

-- -- 0.5 0.5 0.5 0.5 0.5 0.5

1,500 2,000 1,600 1,500 1.750 1.500 I.500 l.50° 2*500 11750

109 -- 109 109 IO9 IO9 109 109 109 109

30 -- -- 30 30 30 30 30 -- 30

8 -- -- 8 -- 8 8 8 -- --

-- -- 1,500 1,500 1,500 1,200 1,500 1,200 1,500 1,500

-- 2,000 -- 1,500 2,000 1,500 2,000 1.500 2,000 2,000

(Btu/lb) 8,000 9,500 8,000 9,000 8.000 9,500 8.000 8,000 8,000 8,000 8,000 8,000 8,700 9,000 8,000 8,000 8.000 8.000 8,000 8,000

Moisture of Extinction (X)

Dead 15 15 20 30 25 15 25 20 25 25 25 15 25 30 30 25 25 25 15 20

Fuel Bed Depth (ft) 0.8 4.5 0.75 2.0 0.4 4.5 1.0 0.3 2.0 1.3 0.6 1.0 3.0 4.0 0.4 3.0 0.25 0.4 1.25 0.5

Wind adjustment factor

0.6 0.5 0.4 0.4 0.5 0.5 0.4 0.4 0.5 0.5 0.5 0.6 0.6 0.5 0.4 0.4 0.4 0.6 0.6 4

S C

max

301 58 32 68 25 24 30 8 65 44 23 178 167 99 14 59 6 17 96 16

*Data for model Q obtained from field measurements by Rod Norum. 1977-1978.

On file with: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Station, Institute of Northern Forestry, 308 Tanana Dr.. Fairbanks AK 99775-5500.
1988 NFDRS Fuel Model Descriptions

Fuel model

Fuel model

parameters A B c D E F G H I J K L N 0 F Q* R s T U

SZB

Load (tons/acre)

l-hour dead 0.2

lo-hour dead --

100-hour dead --

1000-hour dead --

Woody - -

Herbaceous 0.3

Drought 0.2

Surface-area-to-volume rat

l-hour dead 3,000

lo-hour dead --

100-hour dead --

1000-hour dead --

Woody

Herbaceous

-- 1,250 1,500 1,500 1.500 1,250 1.500 1,500

- - - - - - - -

1,500 1.500 1,500 1.500 I.500 1.2oo 1,500 1,500 3,000

- - - - - -

- - 2,500 1.500 2,000 1,500 2,000 2,000 - - 2.000 1,500 2.000 1,500 2.000 I.500 2,000 2.000

Heat content ( ail fuels)

(Btu/lb) 8,000 9,500 8,000 9,000 8,000 9,500 8,000 8,000 8,000 8,000 8,000 8,000 8.700 9.000 8,000 8*ooo 8*ooo 8*ooo 8vooo 81000

Moisture of e x

Dead

tinction (%)

15 15 20 4 0 2 5 15 2 5 2 0 2 5 2 5 2 5 15

1.0

4d

3.0

0.p

0 .:5

/

ld7

I

30

4.0

0.5

0.5

9 9

30

0.4

0.3

0.3

14

18 25 25 15 2 0

3.5 0.4 2.0 1.0 2.5 2.5 1.5 12.0 7.0 2.5 0.25

4.0 1.0 1.0 0.5 2.0 2.0 1.0 12.0 7.0 2.5 --

0.5 -- -- 0.25 1.5 5.0 2.0 10.0 6.0 2.0 --

-- -- -- -- - - 12.0 2.0 12.0 5.5 2.5 --

1.5 0.8 3.0 1.0 7.0 0.5 0.5 -- -- -- --

- - 0.8 1.0 0.5 1.0 0.5 0.5 -- -- -- 0.5

3.5 1.8 1.5 1.5 2.5 5.0 2.0 12.0 7.0 2.5 0.25

0 (l/ft)

700 2.000

109 lo9

30 3o

8 - -

,250 2,000 700 2,000 2,000 1,500 1.500 1.5oo 2.000

109 109 lo9 109 lo9 109 109 109 - -

- - 30 3 0 3 0 3 0 30 30 30 - -

- - - - - - 8 8 8 8 8 - -

1.5 2.0 1.0 2.5 0.5 0.5 1.0 1.5

1.5 3.0 1.0 5.4 0.5 0.5 0.5 1.5

- - 3.0 0.5 2.9 0.5 0.5 -- 1.0

- - 2.0 -- 1.0 -- 0.5 -- --

2.0 7.0 0.5 3.0 0.5 0.5 2.5 0.5

-- -- 0.5 1.0 0.5 0.5 0.5 0.5

2.0 3.5 1.0 3.5 0.5 1.5 1.0 2.0

1,600 1.500 1.750 3,500 1,500 1.500 2,500 1~75~

lo9 109 109 109 109 109 109 lo9

-- 30 3 0 3 0 30 30 -- 3 0

-- 8 -- 8 8 8 -- --

Fuel bed depth (ft) 0.8 4.5 0.25 2.0 0.4 4.5

Minimum wind adjustment factor

0.6 0.5 0.3

Maximum wind adjustment factor

0.6 0.5 0.5

0.3 2.0 0.6

0 .,4 0.3 0.5 0.3 0.5

0.4 0.5 0.5

1.0

0.3

0.3

3o

0.3

0.5

0.5

6 5

1.3

o-5

0.5

4 4

0.5

0.5

o-5

301 58 32 6 8 2 5 2 4 8 2 3 178

I

2.0 0.25 0.4 1.25 0.5

0.2 0.3 0.3

0.3 0.5

0.6 0.6

0.6 0.6 0.3

S C 59 6 17 96 16

max

*Data for model Q obtained from field measurements by Rod Norum. 1977-1978.

On file with: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Station, Institute of Northern Forestry, 308 Tanana Dr., Fairbanks AK 99775-5500.
The following series of graphs for 1986 present seasonal BI comparisons

between the 1978 (dotted lines) and 1988 (solid lines) NFDRS fuel models.

Stonyford, CA, and Athens, GA, data were used to illustrate the general

fire-danger profile that can be expected from each model in subhumid western

and humid eastern situations. Obviously all 20 fuel models are not applicable

at both Stonyford and Athens. The profiles are meant only to provide the user

a convenient first assessment. Proper fuel model selection requires similar

work by the user with local weather data.

Because the NFDRS indexes are primarily a function of weather patterns, the

20 fuel models all produce similar profiles for each weather station; however,

they are much different between the two weather stations. Note particularly

that the BI range varies greatly among the fuel models.

Drought response is produced in part by increased dead fuel availability as

duff and litter dry, but it is also significantly affected by the live

herbaceous and woody fuel load, the live fuel moistures, and whether or not the

live woody component is deciduous. The greatest drought response can be

expected from those fuel models that have a relatively high live herbaceous

and/or woody load, with the woody load declared deciduous. For example, the

drought response of fuel model C, for the Athens data, is largely due to

reduction of the greenness factor to about 6 during the driest months. The

greater response of model C for Stonyford results from both low live fuel

moistures and the addition of most of the 1.8 tons of dead "drought" fuel when

the KBDI approached 800. The KBDI profiles are presented for reference.

The following tabulation defines the options selected to produce the 1988

NFDRS profiles.

- ‘I--- - - .-._ _.- . - - _..- .--.. --- .- -_ -

Fuel

model

A

B

C

D

E

F

G

H

I

J

K

L

N

0

P

Q

R

S

T

U

Fine-dead fuel

moisture equal

fuel stick

moisture

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Deciduous or

evergreen

N/A

Evergreen

Deciduous

Evergreen

Deciduous

Evergreen

Deciduous

Deciduous

WA

N/A

N/A

N/A

Evergreen

Evergreen

Deciduous

Deciduous

Deciduous

Evergreen

Evergreen

Deciduous

Annual or

perennial

herbaceous

Annual

N/A

Perennial

Perennial

Perennial

Perennial

Perennial

Perennial

N/A

N/A

N/A

Perennial

N/A

N/A

Perennial

Perennial

Perennial

Perennial

Perennial

Perennial

2 3
APPENDIX B: TECHNICAL DOWMENTATION

Response to Drought

1. Calculate the fraction of predrought dead fuel load for each size class:

Fi = Wi/Wd

where

Fi = frac.tion of the dead load in the i

t h dead fuel size class

'i = load of the ith dead fuel size class

'd = total predrought dead fuel load for the fuel model

2. Calculate the packing ratio for the fuel model.

R = Wt/Do

where

R = the packing ratio

Wt

= total predrought live and dead load for the fuel model

DO

= the predrought fuel bed depth

3. Calculate the total dead fuel load to add per unit increase in the

KBDI above 100.

ui = w/(800-100) = w/700

where

'i = unit increase of dead fuel load per unit increase in the KBDI

above 100

w= potential total dead fuel load that could be add due to drought

2 4
4. Calculate the dead fuel load to be added to each dead fuel class, at the

current KBDI value.

Wa = (Kc-1OO)U.1

Wj = W. + FiWa 1

where

'a = total dead fuel load to be added at the current level of

drought

KC

= today's KBDI

W . =-drought-induced load of the j

t h dead fuel class

J

5. Calculate the depth required to preserve the predrought packing ratio

Dd = ( W ld-Wl,OOO)'R

where

Dd = fuel bed depth at the current level of drought

'ld = total live and dead load at the current level of drought

wl,ooo = the l,OOO-hour dead fuel load

From this point on, the algorithms that calculate SC and ERC are used

unchanged.

Effect of Greenness Factor on Live Fuel Moisture Calculations

Season of the year, as entered by the user, defines which of the following

live fuel moisture calculation procedures is followed.

1. Winter. Live herbaceous and woody moistures are set to their minimums.

Greenness factor values are 0.

Mh = Mfd

MW = Mcm

where

Mh = live herbaceous moisture content (percent)

Mfd = fine dead fuel moisture (percent)

Mw = live woody fuel moisture (percent)

M

cm

= dormant-season woody moisture for the weather stations'

climate class (50, 60, 70, 80 for climate classes 1, 2, 3, 4)

2 5
2. Spring. Live woody and herbaceous fuel moistures are increasing rapidly

as greenness factor values increase from 1 to 20.

The equation for live herbaceous moisture calculation is

Mh = MspGg/20

where

Mh = 1988 NFDRS live herbaceous moisture (percent)

M

sP

= live herbaceous moisture as calculated in the 1978 NFDRS for

spring greening conditions

G

g

= current live herbaceous greenness factor

The equation for live woody moisture calculation is

MW

= MwoGw/20

where

MW

= 1988 NFDRS live woody moisture (percent)

M

wo

= live woody moisture as calculated in the 1978 NFDRS

GW

= current live woody greenness factor

3. summer. Live herbaceous and woody moistures fluctuate in response to

drying and wetting cycles. Greenness factor values vary between 0 and 20.

Annual herbaceous vegetation should cure sometime during this period.

The equation for live herbaceous moisture calculation is

Mh = MsuGg/20

where

M

su

= live herbaceous moisture as calculated in the 1978 NFDRS, for

the growing season, after completion of greening

The equation for live woody moisture calculation is

MW

= MwoGw/20

2 6
4. Fall. Live herbaceous and woody moistures are decreasing. Vegetation is

entering dormancy.

Calculation for live herbaceous moisture is

Mh = MsuGg/20

where

M

su

= live herbaceous moisture as calculated for transition

conditions in the 1978 NFDRS.

Calculation for live woody moisture is

MW

= MwoGw/20

Dynamic live woody fuel load--In addition to the above changes in live fuel

moisture calculations, the revised NFDRS provides the option to define live

woody fuel as being either deciduous (dynamic) or evergreen (static). If the

evergreen option is selected, the live woody load remains constant at all live

woody fuel moistures. If the deciduous option is selected, the live woody load

is transferred between the live woody class and the fine dead fuel class as a

function of the live woody greenness factor, where:

W

tf = (l-Gw/20)Wl

where

W

tf = live woody load to be transferred to the fine dead class

Wl = total live woody load in the fuel model

The fraction of the live woody load not moved to the fine dead fuel class

remains in the live woody class.

2 7
Variable wind adjustment factor-- The wind adjustment factor varies seasonally

when the live woody vegetation is designated to be deciduous. In this case the

wind adjustment factor is set to its maximum value during the winter. This

provides the minimum midflame windspeed adjustment. During the spring it

decreases, and during the fall it increases, as a function of the woody

greenness factor. During the summer it is set to its minimum value. It is

held constant all year if the live woody vegetation is designated to be

evergreen.

W

rf = wmx - (Wmx-Wmn)Gw/20

where

W

rf = wind adjustment factor

W

mx

= maximum value for the wind adjustment factor

W

mn

= minimum value for the wind adjustment factor

If more than 0.1 inch of precipitation occurred either on the current or the

previous day, the wind adjustment factor is multiplied by 0.3 to reduce the

sensitivity of the NFDRS to wind immediately following a rain.

Fine Dead Fuel Moisture

The user has an option of whether or not to set fine dead fuel moisture

equal to the measured fuel stick moisture. If this option is not selected,

then the fine dead fuel moisture will be equal to the lo-hour timelag fuel

moisture only on the day of and the day following precipitation. Standard fuel

moisture sticks provide the best method to obtain lo-hour timelag moisture, but

if they are not used, the fine dead fuel moisture calculation is modified as

follows:

M1 = 1.03~~~0.8 + M1oo"'2

where

MI = fine dead fuel moisture

E

mc

= equilibrium fuel moisture

MlOO = 100 hour timelag fuel moisture

2 8
-

-.llc...rr,

I I r

0

.-4 8 8

29
2 BURNING INDEX

ATHENS 1986

MODEL B

80 /

72

64

56

BURNING INDEX

ATHENS 1986

MODEL C

50

BURNING INDEX

STONYFORD 1986

MODEL B

200 I

180

160

140

120

100

80

60

40

20

00

BURNING INDEX

STONYFORD 1986

MODEL C

60

5 4

48

42

36

30

24

18

12

06

00
I

.............. .:;;-,.,.,“~.~

;::::‘::I::“.’

........... ............. 11111 k

..................
CJJ

E3 BURNING INDEX

ATHENS 1986

BURNING INDEX

STONYFORD 1986

100 MODEL F

90

80

70

60

50

40

30

20

1 0

00

BURNING INDEX BURNING INDEX

ATHENS 1986 STONYFORD 1986

6o 1

MODEL G

160

140

120

100

80

60

40

20

00

110 MODEL G

IYHI. :.. Y .,,,,,., -wJB d. ..!!:‘. I I I 111

1JAi-i IFEBIMAR~APR~MAYIJUN~JUL lAUGISEPlOCTlNOVlDEC
A

I I 1 , , , , , ,

I I

. . . .

-

I I
I 1 r I I I , , ,
........ ..j.

-2

...... x* .....................
1

_ a: . . . . . . . . . . .

--‘.’ l a

. . ..a

0

- s 8

36
. .‘.’ za....:::::;.\,. . . . . a
I I

c: . . . . . . .

-4c F

............

............ .
-

i-2ss2 i-4z

In0

g .+e tz ::

t? U. S. GO\?ERh?MENT PRINTIKG OFFICE: 1988-535-787 3 9

Burgan, Robert E.

1988 Revisions to the 1978 National Fire-Danger Rating

System. Res. Pap. SE-273. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest

Experiment Station; 1988. 39 pp.

The 1978 National Fire-Danger Rating System does not work well

in the humid environment of the Eastern United States. System

modifications to correct problems and their operational impact

on System users are described. A new set of 20 fuel models is

defined and compared graphically with the 1978 fuel models.

Technical documentation of System changes is provided.

- -T------------I----- - ---- -1

i

Burgan, Robert E. I

I 1988 Revisions to the 1978 National Fire-Danger Rating I

I System. Res. Pap. SE-273. Asheville, NC: U.S. Depart- I

I

ment of Agriculture, Forest Service, Southeastern Forest

Experiment Station: 1988. 39 pp.

I

i

I

The 1978 National Fire-Danger Rating System does not work well 1

1

in the humid environment of the Eastern United States. System

modifications to correct problems and their operational impact I

I on System users are described. A new set of 20 fuel models is I

I

defined and compared graphically with the 1978 fuel models.

Technical documentation of System changes is provided. I

I I

Keywords: Fire potential, fire, wild-land fire, fuel, moisture, I Keywords: Fire potential, fire, wild-land fire, fuel, moisture,

weather. weather. I

I I

I I
The Forest Service, U.S. Department of

Agriculture, is dedicated to the principle of

multiple use management of the Nation’s forest resources

for sustained yields of wood, water, forage, wildlife, and

recreation. Through forestry research, cooperation with the

States and private forest owners, and management of the

National Forests and National Grasslands, it strives-as

directed by Congress-to provide increasingly greater

service to a growing Nation.

USDA policy prohibits discrimination because of race,

color, national origin, sex, age, religion, or handicapping

discriminated against in any USDA-related activity should

immediately contact the Secretary of Agriculture,

Washington, DC 20250.