This page visualizes fire spread rates for each of the Anderson 13 fuel models. Each contour plot shows how spread rate varies with wind speed (0-60 mph) and terrain slope (0-45 degrees) under head fire conditions with 10% fuel moisture.

Code 
using Pkg
Pkg.activate(joinpath(@__DIR__, ".."))

using MarshallWildfire
using GLMakie

output_dir = joinpath(@__DIR__, "images")
mkpath(output_dir)
"/home/runner/work/MarshallWildfire.jl/MarshallWildfire.jl/report/images"

5.1 Grass Group (Models 1-3)

Fast-spreading fuels dominated by grasses. These fuels typically have the highest spread rates due to their fine structure and low moisture content.

Code 
path = joinpath(output_dir, "fuel_model_1.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[1]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 1: Short Grass
Code 
path = joinpath(output_dir, "fuel_model_2.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[2]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 2: Timber Grass/Understory
Code 
path = joinpath(output_dir, "fuel_model_3.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[3]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 3: Tall Grass

5.2 Shrub Group (Models 4-7)

Brush and chaparral fuels. Model 4 (chaparral) produces some of the most extreme fire behavior.

Code 
path = joinpath(output_dir, "fuel_model_4.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[4]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 4: Chaparral
Code 
path = joinpath(output_dir, "fuel_model_5.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[5]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 5: Brush
Code 
path = joinpath(output_dir, "fuel_model_6.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[6]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 6: Dormant Brush
Code 
path = joinpath(output_dir, "fuel_model_7.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[7]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 7: Southern Rough

5.3 Timber Litter Group (Models 8-10)

Compact forest floor fuels. Generally slower spreading due to compact fuel beds.

Code 
path = joinpath(output_dir, "fuel_model_8.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[8]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 8: Closed Timber Litter
Code 
path = joinpath(output_dir, "fuel_model_9.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[9]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 9: Hardwood Litter
Code 
path = joinpath(output_dir, "fuel_model_10.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[10]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 10: Timber with Understory

5.4 Slash Group (Models 11-13)

Logging debris and slash fuels. Can produce intense fires with high fuel loads.

Code 
path = joinpath(output_dir, "fuel_model_11.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[11]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 11: Light Logging Slash
Code 
path = joinpath(output_dir, "fuel_model_12.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[12]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 12: Medium Logging Slash
Code 
path = joinpath(output_dir, "fuel_model_13.png")
if !isfile(path)
    fuel = MarshallWildfire.FUEL_MODELS[13]
    fig = MarshallWildfire.plot(fuel)
    save(path, fig)
end

Model 13: Heavy Logging Slash

5.5 Fuel Model Properties

The following table summarizes the key properties of each Anderson 13 fuel model:

Model Name Fuel Load (kg/m²) SAV Ratio (1/m) Mx (%) Depth (m)
1 Short grass 0.166 11,483 12 0.305
2 Timber grass/understory 0.896 9,843 15 0.305
3 Tall grass 1.345 4,921 25 0.762
4 Chaparral 2.242 6,562 20 1.829
5 Brush 0.448 6,562 20 0.610
6 Dormant brush 0.673 5,741 25 0.762
7 Southern rough 0.507 5,741 40 0.762
8 Closed timber litter 0.673 6,562 30 0.061
9 Hardwood litter 1.307 8,203 25 0.061
10 Timber w/ understory 1.345 6,562 25 0.305
11 Light logging slash 0.673 4,921 15 0.305
12 Medium logging slash 1.794 4,921 20 0.701
13 Heavy logging slash 3.140 4,921 25 0.914

Source: Anderson, H. E. (1982). Aids to Determining Fuel Models for Estimating Fire Behavior. USDA Forest Service General Technical Report INT-122. Values converted to SI units.

Key: - Fuel Load (w₀): Total dry weight of fuel per unit area - SAV Ratio (σ): Surface-area-to-volume ratio - higher values indicate finer fuels that ignite more easily - Mx: Dead fuel moisture of extinction - fires won’t spread if fuel moisture exceeds this value - Depth (δ): Fuel bed depth

5.6 Fuel Moisture

Fuel moisture content is critical for fire behavior. The moisture of extinction (Mx) defines the threshold above which fire will not spread. The plots above assume 10% fuel moisture, representing dry conditions.

5.6.1 Marshall Fire Fuel Moisture

100-hour dead fuel moisture refers to the moisture content of dead woody fuels with diameters between 1-3 inches (2.5-7.6 cm), such as branches and small logs. The “100-hour” designation indicates the timelag—approximately how long (in hours) it takes for these fuels to reach equilibrium with atmospheric moisture conditions. Larger fuels respond more slowly to weather changes, while finer fuels (1-hour, 10-hour) respond more quickly.

The map below shows 100-hour dead fuel moisture from gridMET on December 30, 2021 (the day of the Marshall Fire). Lower values indicate drier, more flammable conditions.

Code 
path = joinpath(output_dir, "fuel_moisture.png")
if !isfile(path)
    @info "Generating fuel_moisture.png"
    MarshallWildfire.plot_fuel_moisture(; output_dir)
else
    @info "fuel_moisture.png already exists"
end;

Fuel Moisture on Fire Day

The exceptionally low fuel moisture values on December 30, 2021 contributed to the rapid spread of the Marshall Fire.