Fuel Ranking Maps and Data

Fuel Rank map for a portion of Riverside County

Fuel Rank Background

CDF has developed a Fuel Rank assessment methodology for the California Fire Plan to identify and prioritize pre-fire projects that reduce the potential for large catastrophic fire. The fuel ranking methodology assigns ranks based on expected fire behavior for unique combinations of topography and vegetative fuels under a given severe weather condition (wind speed, humidity, and temperature). The procedure makes an initial assessment of rank based on an assigned fuel model and slope.

Fuel Rank Diagram

See Techniques, Part 1

Then raises ranks based on the amount of ladder and/or crown fuel present to arrive at a final fuel rank.

Fuel Rank Diagram

See Techniques, Part 2

Fuel Rank
CDF pre-fire engineers verify these rankings and use this fuel rank assessment in conjunction with three additional Fire Plan assessments (weather, assets at risk and level of service).

Fuel Rank
Rank Description
1 Moderate
2 High
3 Very High


Techniques for Fuel Rank Maps and Data, Part 1

The procedure makes an initial assessment of fuel rank based on an assigned fuel model (see surface fuels) and slope.

Fuel Rank Diagram

Table 1 shows the surface rank, from Moderate to Very High, for unique combinations of surface fuel model and six different slope classes (0-10%, 11-25%, 26-40%, 41-55%, 56-75%, > 76) as derived from USGS 7.5 minute Digital Elevation Models (DEM).

Surface Rank
Rank Description
1 Moderate
2 High
3 Very High


The surface ranks were assigned according to the rate of spread and heat per unit area associated with each unique fuel model-slope combination. Figure 1 plots these two important fire behavior parameters as calculated by BEHAVE for the various fuel model and slope class combinations. Fuel model-slope combinations plotted above and to the right of the blue line received a rank of 3, (Very High), those between the blue and red lines received a rank of 2 (High) and those below and to the left of the red line, a rank of 1.

Fire Behavior Characteristics Graph

Techniques for Fuel Rank Maps and Data, Part 2

The procedure makes an initial assessment of fuel rank based on an assigned fuel model and slope (see Techniques, Part 1). Then raises ranks based on the amount of ladder and/or crown fuel present to arrive at a final fuel rank. (See Techniques, Part 1 for Surface Rank.)

Fuel Rank Diagram

Ladder and Crown Fuel Indices

Estimates of ladder and crown fuels support assessment of crown fire potential. The ladder and crown fuel indices estimate the relative abundance of these fuels. These indices measure in a rough manner the probability that individual tree torching and/or crown fire would occur if the stand experienced a wildfire during extreme weather conditions. The indices take values ranging from 0 to 2, with 0 indicating "absent", 1 representing "present but spatially limited", and 2 indicating "widespread".

Ladder and Crown Fuel Indices
0 Not Present
1 Present But Spatially Limited
2 Widespread


The surface rank is raised a maximum of one rank level to yield the final rank if the sum of the ladder index and crown index is greater than or equal to 2. Otherwise the final fuel rank is identical to the initial surface rank. Table 2 shows all possible relationships between surface rank, ladder and crown fuel indices and final fuel rank. For instance, lodgepole pine types modeled as fuel model 8 have a moderate surface rank on all slopes. However, the presence of ladder fuels in areas of dense canopy cover would result in a final fuel rank one class higher than the surface rank (high instead of moderate) in such areas.

Ladder and crown fuel indices are assigned to areas in two ways:
  • If the vegetation data provide sufficient structural detail, the method assigns these additional indices from those data.
  • If the vegetation data lack structural detail, the method assigns indices based on the fuel model. Table 3 provides an example of the ladder and crown fuel indices assigned to fuel models found in Riverside Ranger Unit. The relationship between a given fuel model and the ladder and crown fuel indices is not constant across the state, but may vary for each Ranger Unit as a result of field validation.

Sample Fuel Rank Map

Sample Fuel Rank Map

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