Appendix A
Fire Behavior Potential Analysis Methodology
PURPOSE
The purpose of this appendix is to describe the methodology used to estimate the physical hazard
of fuels in proximity to structures and to combine those data with an evaluation of the values at
risk.
Figure 1: Model Description
BEHAVE MODELING
The wildfire behavior potential analysis assigns a relative ranking to locations based upon
expected surface fire intensity and rate of spread. The model inputs for surface fire behavior
include aspect, slope, elevation, canopy cover, and fuel type. Calculations are based on the
USDA Forest Service's fire behavior model BEHAVE. BEHAVE is a nationally recognized set
of calculations to estimate a fires intensity and rate of spread given certain conditions of
topography, fuels and weather.
1
The BEHAVE modeling system has been used for a variety of applications including prediction
of an ongoing fire, prescribed fire planning, fuel hazard assessment, initial attack dispatch, and
fire prevention planning and training. Predictions of wildland fire behavior are made for a single
point in time and space given simple user-defined fuel, weather and topography.
Assumptions of BEHAVE
Fire is predicted at the flaming front
Fire is free burning
Behavior is heavily weighted toward the fine fuels
Continuous and uniform fuels
Surface fires
FLAMMAP
Anchor Point uses FlamMap developed by Systems for Environmental Management (Missoula,
Montana) and the Fire Sciences Laboratory of the Rocky Mountain Research Station (USDA
Forest Service, Missoula, Montana) to evaluate the potential fire conditions in the study area.
The Four Mile Canyon study area encompasses approximately 12,800 acres, which are broken
down into 10 meter (m) grids. Using FlamMap's spatial analysis capabilities, each 10 meter
square (sq) grid is queried for its elevation, slope, aspect and fuel type. These values are input
into FlamMap, along with reference weather information. The outputs of FlamMap include the
estimated Rate of Spread (ROS), Flame Length (FL) (from BEHAVE) and Crown Fire Activity
for a fire in that 10m sq grid. The model computes these values for each grid cell in the study
area. These values are then reclassified into Wildfire Hazard classes of None, Low, Moderate,
High, Very High, and Extreme.
2
FIRE BEHAVIOR INPUTS
Fire behavior is dependant upon aspect, slope, elevation, canopy cover and fuel type. The
following pages contain an explanation of each.
Figure 2: Slope
Slopes are shown here as percent (rise/run x100). Steeper slopes intensify fire behavior and thus
will contribute to a high wildfire hazard rating.
Figure 3: Aspect
Aspects are shown as degrees from North ranging from 0 to 360 according to their orientation.
Classification North East South West
Range 315-45 45-135 135-225 225-315
3
Figure 4: Elevations
Elevations within Four Mile FPD vary from 5,300 to over 9,000. As elevation increases, fuel
loading and available oxygen for combustion change. Above tree line fuels become sparse and
the natural burn interval is measured in centuries.
Figure 5: Canopy Cover
Canopy cover is the horizontal percentage of the ground surface that is covered by tree crowns.
Canopy cover is measured as the horizontal fraction of the ground that is covered directly
overhead by tree canopy. Coverage units are in four categories. 1=1-20%. 2=21-50%. 3=50-80%.
4= 81-100%.
4
Fuel Models
Fuel models are a set of numbers that describe the fuel in terms that a fire spread model can use.
There are seven characteristics used to categorize fuel models:
Fuel Loading
Size and Shape
Compactness
Horizontal Continuity
Vertical Arrangement
Moisture Content
Chemical Content
Description
The study area is represented primarily by five fuel models (FM): FM 1, 2, 8, 9 and 10
(Anderson, 1982). Fuel models 5 and 6 exist, but not in enough quantity to significantly
influence fire behavior. Each of the major fuel types present are described below with a table
showing a range of fire behavior based on the BEHAVE system. Figure 18 displays the fuel
types graphically for Four Mile Canyon.
The BEHAVE Fire Behavior Prediction and Fuel Modeling System was used to help determine
the wildfire hazard for this study. It has been used for a variety of applications including
prediction of an ongoing fire, prescribed fire planning, fuel hazard assessment, initial attack
dispatch, fire prevention planning and training. Predictions of wildland fire behavior are made
for a single point in time and space given simple user-defined fuel, weather, and topography.
Requested values depend on the modeling choices made by the user. For example, fuel model,
fuel moisture, wind speed and direction, and terrain and slope are used to calculate rate of
spread, flame length and intensity. For a complete discussion of the fuel typing and BEHAVE
modeling used in this study please refer to Appendix A.
Figure 18: Four Mile Canyon Fuels Map
5
FUEL MODEL 11
Figure 19: Annual Grasses
Characteristics
Grasslands and savanna are represented along with stubble, grass-tundra and grass-shrub
combinations.
Common Types/Species
Annual and perennial grasses are included in this fuel model. Refer to Figure 16 for illustrations.
Fire Behavior
Fire spread is governed by the fine, very porous and continuous herbaceous fuels that have cured
or are nearly cured. Fires in this fuel model are surface fires that move rapidly through the cured
grass and associated material. Very little shrub or timber is present, generally less than one-third
of the area.
1 Anderson, Hal. 1982. Aids to Determining Fuel Models for Estimating Fire Behavior. Gen. Tech. Rep. INT-122.
Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station 22 p. (NFES 1574).
6
Rate of spread in chains/hour (1 chain=66 ft)
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 28.8 92.9 203.6 362.4 570.1 665.6
re %
4.0 22.0 71.1 155.7 277.0 345.1 345.1
6.0 19.4 62.4 136.8 243.4 270.1 270.1
8.0 16.7 53.9 118.1 198.7 198.7 198.7
10.0 11..0 35.6 64.8 64.8 64.8 64.8
10 hr fuel=5%, 100 hr fuel=6%, herbaceous fuel moisture=100%, slope=10%
Flame Length in Feet
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 3.0 5.1 7.3 9.6 11.8 12.7
re %
4.0 2.4 4.1 5.9 7.8 8.6 8.6
6.0 2.2 3.8 5.5 7.1 7.5 7.5
8.0 2.0 3.4 4.9 6.3 6.3 6.3
10.0 1.4 2.4 3.2 3.2 3.2 3.2
7
FUEL MODEL 22
Figure 20: Timber with Grass Understory
Characteristics
This fuel model consists of open grown pine stands. Trees are widely spaced with few understory
shrubs or regeneration. Ground cover consists of mountain grasses and/or needles and small
woody litter. This model occurs in open-grown and mature Ponderosa pine stands in the Foothill
to Montane zone.
Common Types/Species
The predominate tree species is Ponderosa pine and may include some scattered Douglas fir.
Other tree and shrub species include Common and Rocky Mountain Juniper, Buckbrush, Bitter
brush and Mountain Mahogany. Mountain grasses are included in this model.
Fire Behavior
Surface fires in this fuel model spread easily. Clumps of fuel may generate higher fire intensities.
Fire is carried by grasses and/or woody litter.
2 Anderson, Hal. 1982. Aids to Determining Fuel Models for Estimating Fire Behavior. Gen. Tech. Rep. INT-122.
Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station 22 p. (NFES 1574).
8
Rate of spread in chains/hour (1 chain=66 ft)
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 12.4 34.2 67.5 111.6 166.0 230.2
re %
4.0 10.2 28.0 55.3 91.4 135.9 188.5
6.0 9.0 24.9 49.1 81.2 120.8 167.6
8.0 8.3 22.9 45.3 74.9 111.3 154.4
10.0 7.4 20.5 40.5 67.0 99.7 138.3
12.0 5.9 16.3 32.3 53.3 79.3 110.0
10 hr fuel=5%, 100 hr fuel=6%, herbaceous fuel moisture=100%, slope=10%
Flame Length in Feet
Mid-flame Wind Speed
% Fine Dead Fuel mo 2.0 4.0 6.0 8.0 10.0 12.0
2.0 4.3 6.9 9.4 11.8 14.2 16.5
4.0 3.7 5.8 8.0 10.1 12.1 14.0
6.0 3.4 5.4 7.3 9.2 11.1 12.9
istu 8.0 3.2 5.1 6.9 8.7 10.5 12.2
re 10.0 2.9 4.7 6.4 8.1 9.7 11.2
12.0 2.4 3.9 5.3 6.7 8.0 9.3
9
FUEL MODEL 83
Figure 21: Timber Litter, Light Fuel Load
Characteristics
This fuel model is represented by closed canopy stands of Lodgepole pine or Ponderosa pine
with little under growth. Amounts of needle and woody litter are also low. This fuel model
occurs at higher elevations in the Montane zone.
Common Types/Species
This fuel model is most often represented by Lodgepole pine but Ponderosa pine can be
included. There are little or no understory plants.
Fire Behavior
Fires in this fuel model are slow burning, low intensity fires burning in surface fuels. Fuels are
mainly needles and woody litter. Heavier fuel loadings can cause flare-ups. Heavier fuel loads
have the potential to develop crown fires in extreme burning conditions.
3 Anderson, Hal. 1982. Aids to Determining Fuel Models for Estimating Fire Behavior. Gen. Tech. Rep. INT-122.
Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station 22 p. (NFES 1574).
10
Rate of spread in chains/hour (1 chain=66 ft)
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 1.1 2.3 3.9 5.7 7.8 10.1
re %
4.0 0.9 1.9 3.2 4.7 6.4 6.9
6.0 0.7 1.6 2.6 3.9 4.9 4.9
8.0 0.6 1.4 2.3 3.4 3.8 3.8
10.0 0.6 1.2 2.0 3.0 3.1 3.1
12.0 0.5 1.1 1.8 2.7 2.7 2.7
10 hr fuel=5%, 100 hr fuel=6%, herbaceous fuel moisture=100%, slope=10%
Flame Length in Feet
Mid-flame Wind Speed
% Fine Dead Fuel mo 2.0 4.0 6.0 8.0 10.0 12.0
2.0 0.9 1.3 1.7 2.0 2.3 2.6
4.0 0.8 1.1 1.4 1.7 2.0 2.0
6.0 0.7 1.0 1.2 1.5 1.7 1.7
istu 8.0 0.6 0.9 1.1 1.3 1.4 1.4
re 10.0 0.6 0.8 1.0 1.2 1.3 1.3
12.0 0.6 0.8 1.0 1.2 1.3 1.3
11
FUEL MODEL 94
Figure 22: Timber Litter, (note heavier surface fuels).
Characteristics
Both long-needle conifer stands and hardwood stands, especially the oak-hickory types, are
typical. Concentrations of dead-down woody material will contribute to possible torching out of
trees, spotting and crowning.
Common Types/Species
Closed stands of long-needled pine like Ponderosa, Jeffrey, and Red pines, or southern pine
plantations are grouped in this fuel model.
Fire Behavior
Fires in this fuel model run through the surface litter faster than model 8 and have longer flame
height. Fall fires in hardwoods are predictable, but high winds will actually cause higher rates of
spread than predicted because of spotting caused by rolling and blowing leaves.
4 Anderson, Hal. 1982. Aids to Determining Fuel Models for Estimating Fire Behavior. Gen. Tech. Rep. INT-122.
Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station 22 p. (NFES 1574).
12
Rate of spread in chains/hour (1 chain=66 ft)
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 4.0 9.8 18.1 28.7 41.5 56.2
re %
4.0 3.2 7.7 14.3 22.7 32.7 44.4
6.0 2.6 6.4 11.8 18.8 27.1 36.7
8.0 2.3 5.5 10.2 16.3 23.5 31.8
10.0 2.0 5.0 9.2 14.7 21.2 28.7
12.0 1.9 4.6 8.5 13.5 19.5 26.5
10 hr fuel=5%, 100 hr fuel=6%, herbaceous fuel moisture=100%, slope=10%
Flame Length in Feet
Mid-flame Wind Speed
% Fine Dead Fuel mo 2.0 4.0 6.0 8.0 10.0 12.0
2.0 2.3 3.5 4.7 5.8 6.8 7.9
4.0 1.9 2.9 3.9 4.8 5.7 6.6
6.0 1.7 2.5 3.4 4.2 5.0 5.7
istu 8.0 1.5 2.3 3.1 3.8 4.5 5.2
re 10.0 1.4 2.2 2.9 3.5 4.2 4.8
12.0 1.4 2.1 2.7 3.4 4.0 4.6
13
Fuel Model 105
Figure 23: Timber Litter, (note heavier fuels and understory)
Characteristics
This fuel model is represented by dense stands of over-mature Ponderosa pine, Lodgepole pine,
mixed conifer and continuous stands of Douglas fir. In all stand types heavy downed material is
present. There is also a large amount of dead-down woody fuels. Reproduction of vegetation
may be present, acting as ladder fuels. This fuel model includes stands of budworm killed
Douglas fir, closed stands of Ponderosa pine with large amounts of ladder and surface fuels.
Stands of Lodgepole pine with heavy loadings of downed trees are also present. This fuel model
can occur from the foothills through the sub-alpine zone.
Common Types/Species
All types of vegetation can occur in this fuel model, but primary species are: Douglas fir,
Ponderosa pine and Lodgepole pine.
Fire Behavior
Fire intensities in this fuel model can be moderate to extreme. Fire moves through dead, downed
woody material. Torching of trees and spot fires are more frequent. Crown fires are quite
possible.
5 Anderson, Hal. 1982. Aids to Determining Fuel Models for Estimating Fire Behavior. Gen. Tech. Rep. INT-122.
Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station 22 p. (NFES 1574).
14
Rate of spread in chains/hour (1 chain=66 ft)
Mid-flame Wind Speed
moistu Fine Dead Fuel 2.0 4.0 6.0 8.0 10.0 12.0
2.0 3.8 8.2 13.7 20.1 27.3 35.1
re %
4.0 3.3 7.2 12.1 17.8 24.1 31.0
6.0 3.0 6.6 11.0 16.1 21.8 28.0
8.0 2.8 6.1 10.2 14.9 20.2 26.0
10.0 2.6 5.7 9.6 14.1 19.1 24.5
12.0 2.5 5.5 9.2 13.4 18.2 23.4
10 hr fuel=5%, 100 hr fuel=6%, herbaceous fuel moisture=100%, slope=10%
Flame Length in Feet
Mid-flame Wind Speed
% Fine Dead Fuel mo 2.0 4.0 6.0 8.0 10.0 12.0
2.0 3.8 5.5 7.0 8.3 9.5 10.7
4.0 3.5 5.0 6.3 7.5 8.6 9.7
6.0 3.2 4.6 5.8 6.9 7.9 8.9
istu 8.0 3.0 4.3 5.5 6.5 7.5 8.4
re 10.0 2.9 4.1 5.2 6.2 7.2 8.0
12.0 2.8 4.0 5.1 6.0 6.9 7.8
15
REFERENCE WEATHER
Weather for FlamMap was created by using weather data collected in Boulder.
Latitude (dd mm ss) 40 ° 01 ' 05 " N
Longitude (dd mm ss) 105 ° 21 ' 38 " W
Elevation (ft.) 6,775
The mean for each variable (1 hr, 10 hr, and 100 hr fuel moisture, woody fuel moisture,
herbaceous fuel moisture, and wind speed) was calculated for the months of May-October for the
years 1992-2002. Then, the average of each mean/month was calculated to represent an average
fire season day.
The "extreme conditions maps were calculated using ninetieth percentile weather data. That is
to say, the weather conditions existing on the eighteen most severe fire weather days in each
season for the ten-year period were averaged together. It is reasonable to assume that similar
conditions may exist for at least eighteen days of the fire season during an average year. In fact,
during extreme years such as 2000 and 2002, such conditions may exist for significantly longer
periods. Even these calculations may be conservative compared to observed fire behavior.
Drought conditions the last few years have significantly changed the fire behavior in dense forest
types such as mixed conifer. The current values underestimate fire behavior especially in the
higher elevation fuels because the extremely low fuel moistures are not represented in the
averages. The following values were used in FlamMap:
Average Weather Conditions
Variable Value
20 ft Wind speed up 25 mph
slope
Herbaceous fuel moisture 57%
Woody fuel moisture 110%
100 hr fuel moisture 11%
10 hr fuel moisture 9%
1 hr fuel moisture 7%
Canopy height 15 m
Crown base height 1 m
Crown bulk density 0.1 kg/m3
Foliar moisture 100%
content
16
FIRE BEHAVIOR ANALYSIS OUTPUTS
From the fire behavior analysis predictions of crown fire activity, rate of spread and flame length
are derived. Rate of spread and flame length predictions are combined to produce the fire
behavior potential map that shows the results of the analysis.
Figure 6: Predictions of Crown Fire Activity (Average Weather Conditions)
Crown fire activity values are generated by the FlamMap model and classified into 4 categories
based on standard ranges: active, passive, surface, and not applicable.
Figure 7: Predictions of Crown Fire Activity (Extreme Weather Conditions)
17
Figure 8: Spread Rate Predictions (Average Weather Conditions)
Spread rate values are generated by the FlamMap model and classified into four categories based
on standard ranges: 0-20 chains/hour (CPH), 20.1-40 CPH, 40.1-60 CPH, and 60.1-450 CPH.
Figure 9: Spread Rate Predictions (Extreme Weather Conditions)
18
Figure 10: Flame Length Predictions (Average Weather Conditions)
Flame length values are generated by the FlamMap model and classified in the four categories
based on standard ranges: 0-4 feet, 4.1-8 feet, 8.1-11 feet and 11.1-60 feet.
Figure 11: Flame Length Predictions (Extreme Weather Conditions)
19
Figure 12: District Wide Fire Behavior Potential (Average Weather Conditions)
Figure 13: District Wide Fire Behavior Potential (Extreme Weather Conditions)
FIRE BEHAVIOR INTERPRETATION
The Fire Behavior Potential map shows the results of the Wildfire Hazard Evaluation. This
evaluation is a prediction of likely fire behavior given a standardized set of conditions and a
single point source ignition at every point. It does not consider cumulative impacts of increased
fire intensity over time and space. The model does not calculate the probability that a wildfire
will occur. It assumes an ignition occurrence for every cell (a 10 x 10 meter area).
20