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NFDRS
Indices Interpretation The
following is a brief explanation of the National Fire Danger Rating (NFDRS)
indices as used by Georgia Forestry Commission (Table 1). For more details, please refer to the
materials in the references. Table
1: NFDRS for Dallas, Ga on Oct 23, 2002
RH(%): Relative Humidity in
percent IC: The Ignition Component (IC)
is an index within 1988 National Fire Danger Rating System. IC relates the probability that a fire that
requires suppression action will result if a firebrand is introduced into a
fine fuel complex. Theoretically, on a
day when the ignition component registers a 60, approximately 60% of all fire
brands that come into contact with wildland fuels will require suppression
action. BI: Dividing Burning Index (BI)
by 10 gives a reasonable estimate of flame length in feet at the head of a
fire. Burning Index is fuel model
dependent. In Georgia Forestry Commission,
this is the basis for Class Day. Class Day: Class day describes the
potential for wildland fires. Georgia
Forestry Commission uses Burning Index (BI) to determine Class Day. Class Day determination points are station
dependent such that it will reflect the potential of wildland fire in the local
area. Table 3 shows the determination
percentile for all Georgia Forestry Commission weather stations and some of our
cooperator’s weather station. If a
station is not found in the list, its BI is likely to be determined by the Fuel
Model determination points. Definitions of the various fuel models are included
in Appendix A below. Table
2: Class Day determination points
Note: The listed values are the minimum value for
each Class day. For example, when
Watkinsville has BI of 19-21, it has Class 4 Day. KBDI: Keetch-Byram Drough Index
(KBDI) measures moisture in deep duffs or upper soil layers. The relative dryness of soil is important in
fire suppression. KBDI varies from 0
(Wet) to 800 (Dry). Wind
(mph):
10-minute averaged wind speed in mile per hour and wind direction in 8 point
compass, i.e. N, NE, E, SE, S, SW, W, NW and calm. Mx_Wind(mph): Wind gust in mile per hour
and wind direction in 8 point compass, i.e. N, NE, E, SE, S, SW, W, NW and
calm. Mx_Wind has to be at least as
strong as Wind and they should be in the same direction. Rn24(inch): Rainfall amount in the last 24 hours in inches. Dur(Hr): Duration of rainfall in hours if there is
any. Sow: State of weather
Temp(°F): Temperature in Fahrenheit Td(°F): Dew point temperature in
Fahrenheit Tmax(°F): Maximum temperature in the last
24 hours in Fahrenheit Tmin(°F): Minimum temperature in the
last 24 hours in Fahrenheit RHMax(%): Maximum relative humidity
in the last 24 hours in percent RHMin(%): Minimum relative humidity
in the last 24 hours in percent HrbGF: Herbaceous greenup factor
(HrbGF) expresses the actual greening and curing of live herbaceous
vegetation. HrbGF varies from 0
(completely cured) to 20 (completely green).
In
Georgia Forestry Commission, we changed greenup factors automatically by the
time of the year and KBDI. In Winter, greenup
factors are set to zero. From Spring to Autumn,
greenup factors will change gradually, from 0 to 20 and then from 20 to 0. Georgia Forestry Commission defined winter as
from December 21 through March 20 each year. The default greenup factors by the time of a year
are listed in the Table 2. Table
2. Default Greenup factor over a year
In
order to account for dry periods, drought adjusted greenup factor based on KBDI
is adopted from Burgan (1988) (Table 3).
If the default greenup factor exceeds the drought adjusted greenup
factor, greenup factor will be reduced to the drought adjusted greenup
factor. If not, green up factors are
used as is. For example, if KBDI is 395
on August 4, when the default greenup factor is 20, the greenup factor will
adjusted to 10 due to drought. If KBDI is 395 on December 23, when the default green
up factor is 0, the greenup factor will still stay at 0. Table
3. Drought Adjusted greenup factor based on KBDI
WdyGF: Woody greenup factor
(WdyGF) expresses the actual greening and curing of live woody vegetation. WdyGF varies from 0 (completely cured) to 20
(completely green). Please refer to
HrbGF for details. 1-Hour/10-Hour/100-Hour/1000-Hour: Dead fuel moisture content
in fuel that takes 1 hour/10 hours/100 hour/1000 hour to lose or gain 63% of
the difference between the dead fuel itself and the surrounding
atmosphere. Fuel moisture percent is
computed by dividing the weight of "water" in the fuel by the
oven-dried weight of the fuel and then, multiplying by 100 to get to percent. X1000: Predictor value for
1000-Hour Herbaceous: Fuel moisture in live herbaceous
vegetation. Please refer to
"1-Hour" on fuel moisture computation. Woody: Fuel moisture in live woody
vegetation. Please refer to
"1-Hour" on fuel moisture computation. SC: Spread Component (SC) is
the forward rate of spread at the head of the fire in feet per minute. Since 1 chain=66 feet and there are 60
minutes in an hour, so 1 feet per minute is 0.9 chain per hour. Thus, multiply the value of SC by 0.9 gives
the spread rate in chain per hour. EC: Energy Release Component
(EC) is the potential available energy per square foot at the head of the fire
in BTUs per square foot. References: Weather Information Management System (WIMS)
user's manual KBDI Revisited: Prescribed Fire Applications
by Mike Melton published in Fire Management Notes in 1996 Volumne 56, Number 4, p.8-11
KBDI: Can It Help Predict Wildland Fires?
by Daniel Chan, James Paul and Alan Dozier in Fire Management Today 2004, Volumne 64, Number 2, p.39-42
KBDI: A Guide to Fire Conditions & Suppression Prodblems
by Mike Melton published in Fire Management Notes in 1989 Volume 50, Number 4, p.30-34
Bradshaw, Larry S.; Deeming,
John E.;Burgan, Robert E.;Cohen, Jack D., compilers. The 1978 National Fire-Danger Rating
System;technical documentation. General
Technical Report INT-169. Ogden, UT: US
Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment
Station; 1984. 44pp. Burgan, Robert E.; 1988
Revisions to the 1978 National Fire-Danger Rating System. Res. Pap. SE-273. Asheville, NC: US Department of Agriculture, Forest,
Service, Southeastern Forest Experiment Station; 1988. 39pp. APPENDIX
A FUEL MODEL DEFINITIONS Definitions extracted from (Deeming, et al. 1977). FUEL MODEL A This fuel model represents western grasslands vegetated by annual
grasses and forbs. Brush or trees may be present but are very sparse, occupying
less than one third of the area. Examples of types where Fuel Model A should be
used are cheatgrass and medusahead. Open pinyon-juniper, sagebrush-grass, and
desert shrub associations may appropriately be assigned this fuel model if the
woody plants meet the density criteria. The quantity and continuity of the
ground fuels vary greatly with rainfall from year to year. FUEL MODEL B Mature, dense fields of brush 6 feet or more in height are
represented by this fuel model. One-fourth or more of the aerial fuel in such
stands is dead. Foliage burns readily. Model B fuels are potentially very
dangerous, fostering intense, fast-spreading fires. This model is for
California mixed chaparral generally 30 years or older. The F model is more
appropriate for pure chamise stands. The B model may also be used for the New
Jersey pine barrens. FUEL MODEL C Open pine stands typify Model C fuels. Perennial grasses and forbs
are the primary ground fuel but there is enough needle litter and branchwood
present to contribute significantly to the fuel loading. Some brush and shrubs
may be present but they are of little consequence. Situations covered by Fuel
Model C are open, longleaf, slash,ponderosa,Jeffrey, and sugar pine stands.
Some pinyon-juniper stands may qualify. FUEL MODEL D This fuel model is specifically for the palmetto-gallberry
understory-pine overstory association of the southeast coastal plains. It can
also be used for the so-called "low pocosins" where Fuel Model 0
might be too severe. This model should only be used in the Southeast because of
a high moisture of extinction. FUEL MODEL E Use this model after leaf fall for hardwood and mixed
hardwood-conifer types where the hardwoods dominate. The fuel is primarily
hardwood leaf litter. The oakhickory types are best represented by Fuel Model
E, but E is an acceptable choice for northern hardwoods and mixed forests of
the Southeast. In high winds, the fire danger may be underrated because rolling
and blowing leaves are not accounted for. In the summer after the trees have
leafed out, Fuel Model E should be replaced by Fuel Model R FUEL MODEL F Fuel Model F is the only one of the 1972 NFDRS Fuel Models whose
application has changed. Model F now represents mature closed chamise stands and
oakbrush fields of Arizona, Utah, and Colorado. It also applies to young,
closed stands and mature, open stands of California mixed chaparral. Open
stands of pinyon-juniper are represented; however, fire activity will be
overrated at low windspeeds and where there is sparse ground fuels. FUEL MODEL G Fuel Model G is used for dense conifer stands where there is a
heavy accumulation of litter and downed woody material. Such stands are
typically overmature and may also be suffering insect, disease, wind, or ice
damage-natural events that create a very heavy buildup of dead material on the
forest floor. The duff and litter are deep and much of the woody material is
more than 3 inches in diameter. The undergrowth is variable but shrubs are
usually restricted to openings. Types meant to be represented by Fuel Model G
are hemlock-Sitka spruce, Coast Douglas-fir, and windthrown or bug-killed
stands of lodgepole pine and spruce. FUEL MODEL H The short-needled conifers (white pines, spruces, larches, and
firs) are represented by Fuel Model H. In contrast to Model G fuels, Fuel Model
H describes a healthy stand with sparse undergrowth and a thin layer of ground
fuels. Fires in H fuels are typically slow spreading and are dangerous only in
scattered areas where the downed goody material is concentrated. FUEL MODEL I Fuel Model I was designed for clearcut conifer slash where the
total loading of materials less than 6 inches in diameter exceeds 25 tons/acre.
After settling and the fines (needles and twigs) fall from the branches, Fuel
Model I will overrate the fire Potential. For lighter loadings of clearcut
conifer slash, use Fuel Model J, and for light thinnings and partial cuts where
the slash is scattered under a residual overstory, use Fuel Model K. FUEL MODEL J This model complements Fuel Model I. It is for clearcuts and
heavily thinned conifer stands where the total loading of materials less than 6
inches in diameter is less than 25 tons/acre. Again, as the slash ages, the
fire potential will be overrated FUEL MODEL K Slash fuels from light- thinnings and partial cuts in conifer
stands are represented by Fuel Model K. Typically the slash is scattered about
under an open overstory. This model applies to hardwood slash and to southern
pine clearcuts where the loading of all Fuels is less than 15 tons/acre. FUEL MODEL L This fuel model is meant to represent western grasslands vegetated
by perennial grasses. The principal species are coarser and the loadings
heavier than those in Model A fuels. Otherwise the situations are very similar;
shrubs and trees occupy less than one-third of the area. The quantity of fuel
in these areas is more stable from year to year. In sagebrush areas Fuel Model
T may be more appropriate. FUEL MODEL N This fuel model was constructed specifically for the sawgrass
prairies of south Florida. It may be useful in other marsh situations where the
fuel is coarse and reedlike. This model assumes that one-third of the aerial
portion of the plants is dead fast-spreading, intense fires can occur even over
standing water. FUEL MODEL O The O fuel model applies to dense, brushlike fuels of the
Southeast. O fuels, except for a deep litter layer, are almost entirely living
in contrast to B fuels. The foliage burns readily except during the active
growing season. The plants are typically over 6 feet tall and are often found
under an open stand of pine. The high pocosins of the Virginia, North and South
Carolina coasts are the ideal of Fuel Model O.
If the plants do not meet the 6-foot criteria in those areas, Fuel Model
D should be used. FUEL MODEL P Closed, thrifty stands of long-needled southern pines are
characteristic of P fuel: A 2- to 4-inch layer of lightly compacted needle
litter is the primary fuel. Some small diameter branchwood is present but the
density of the canopy precludes more than a scattering of shrubs and
grass. Fuel Model P has the high
moisture of extinction characteristic of the Southeast. The corresponding model
for other long-needled pines is U. FUEL MODEL Q Upland Alaskan black spruce is represented by Fuel Model Q. The
stands are dense but have frequent openings filled with usually inflammable
shrub species. The forest floor is a deep layer of moss and lichens, but there
is some needle litter and small-diameter branchwood. The branches are
persistent on the trees, and ground fires easily reach into the tree crowns.
This fuel model may be useful for jack pine stands in the Lake States. Ground
fires are typically slow spreading, but a dangerous crowning potential exists.
Users should be alert to such events and note those levels of Spread Component
(SC) and BI when crowning occurs. FUEL MODEL R This fuel model represents the hardwood areas after the canopies
leaf out in the spring. It is provided as the off-season substitute for E. It
should be used during the summer in all hardwood and mixed conifer-hardwood
stands where more than half of the overstory is deciduous. FUEL MODEL S Alaskan or alpine tundra on relatively well-drained sites is the S
fuel. Grass and low shrubs are often present, but the principal fuel is a deep
layer of lichens and moss. Fires in these fuels are not fast spreading or
intense, but are difficult to extinguish. FUEL MODEL T The bothersome sagebrush-grass types of the Great Basin and the
Intermountain West are characteristic of T fuels. The shrubs burn easily and
are not dense enough to shade out grass and other herbaceous plants. The shrubs
must occupy at least one-third of the site or the A or L fuel models should be
used. Fuel Model T might be used for immature scrub oak and desert shrub
associations in the West, and the scrub oak-wire grass type in the Southeast. FUEL MODEL U Closed stands of western long-needled pines are covered by this
model. The ground fuels are primarily litter and small branchwood. Grass and
shrubs are precluded by the dense canopy but occur in the occasional natural
opening. Fuel Model U should be used for ponderosa, Jeffrey, sugar pine, and
red pine stands of the Lake States. Fuel Model P is the corresponding model for
southern pine plantations. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||