Calculating Wildfire Hazard Levels—Algebraic Raster Construction Using Spatial Analyst

ArcGIS Spatial Analyst was used to develop a raster grid layer predicting degrees of wildfire hazard levels within a western Colorado fire management zone. The layer was constructed using the Reclassify and Raster Calculator utilities. Slope, aspect, and fuels were considered as factors affecting wildfire behavior. Assigned break and integer values allowed map algebra expressions to derive output cell values based on summed integers and an if-then-else conditional function.

Colorado’s West Zone wildfire management agencies tested electronic and paper versions of the project to anticipate fire behavior, safety concerns, and resource allocations during the 2005 wildfire season. Analysis based on comparisons with historic fire perimeters is proceeding, and development may include weighted calculations of reclassified fuel models within such boundaries. A planned modification of the original algorithm would reclassify south-facing slopes of less than 20 percent to indicate lower hazard ratings. Other considerations might include analysis of remotely sensed vegetative images to take into account the telltale senescence of invasive annuals such as cheatgrass.