Fuel Model Introduction
Link to individual Fuel Model Attributes
Introduction: Fire Behavior Reference for LF Wildland Fuel Guidebook:
The LANDFIRE Program strives to produce consistent and relevant fire behavior fuel model and canopy attribute grids for the U.S. and its Territories. Because of the wide variation in wildland fuels through space and environmental conditions, coarse scale fuel models and site descriptors that will affect the wind are used as fundamental building blocks to depict surface fire characteristics. Once surface fire characteristics are determined the canopy attributes (for areas that have treed canopies) are used to predict the fire’s relationship to the upper stratum of the fuel layer.
The primary purpose for these fuels descriptions is to provide information for fire behavior processors in order to predict and describe the fire behavior on a given site under varying conditions. The LF program currently uses combinations of existing vegetation type (EVT), existing vegetation cover (EVC) and existing vegetation height (EVH) to build most of the rule sets that determine a surface fuel model and canopy attributes. The biophysical setting and fuel disturbance layers are also used in certain cases to better refine the surface fuel model assignment. Within the three main vegetation layers (EVT, EVC, EVH) the lifeform of the pixel and hence the general fuel type is described. In the LF data lifeform is determined from the top of the vegetation structure to the bottom. If a remotely sensed pixel has greater than 10% tree cover it’s considered a treed pixel. If less than 10% tree cover than it is a shrub pixel and if there is less than 10% shrub cover it’s considered an herbaceous pixel. With species information from EVT, the amount of cover from EVC, and the vertical stature of the vegetation with EVH, assumptions can be made to further forecast the fuel type based on the openness or denseness of the vegetation Fuelrule_examples.pdf. For areas with canopy attributes the same vegetation elements are used in algorithm’s to calculate canopy base height (CBH) and canopy bulk density (CBD). LF data is more appropriate for use in the Scott Reinhardt method of crown fire initiation and spread.
In this reference for the Wildland Fuel Guidebook there is a page for each of the Fire Behavior Fuel Model 40 (Scott, Burgan, 2006; FBFM40) accessed through Fuel Model Attributes link. These pages include graphs depicting fire behavior characteristics. These fire behavior characteristics are derived from average fuel moisture/ windspeed, and dry/windier or more extreme conditions. The fire behavior characteristics, rate of spread will be focused on for surface fire and flame length will be used in the case of canopy fire initiation. Canopy fire characteristic for additional rate of spread due to passive and active crowning are graphed by fuel model for passive and active crowning. Then more information is provided on the active crowning page Active_crown_page.pdf. Overall the desired result is the ability for these fuels layers to predict or provide insights to the final extent of a fire whether it is spreading only on the surface, in the crowns, or a combination of the two. While actual fire perimeters may not be used in this evaluation of the fuel layers, the ability to identify the fire type and expected fire growth with consideration of the vegetation information provided under varying environmental conditions is provided and will be important in considering changes to the data.