A Weights-of-Evidence Model for Mapping the Probability of Fire Occurrence in Lincoln County, Nevada

Wildfire is a dynamic ecological process with spatial patterns that reflect multiple influences on fire occurrence and spread. We used weights of evidence techniques to model spatial patterns of wildfire occurrence in relation to landscape-scale drivers of fire in the southern Great Basin. Weights of evidence is a quantitative, data-driven, Bayesian modeling method that can be applied to spatial data for producing maps of expected probability of occurrence. We applied this method to Lincoln County, Nevada, for the period from 1994 to 2005. Fire data were obtained from the National Fire Occurrence Database and from the Bureau of Land Management. Spatial data sets used as potential predictors of fire occurrence included elevation, topography (terrain slope, hillshade illumination, basin vs. range, topographic roughness), geological substrate, vegetation cover type, lightning strike density, annual maximum temperature and total precipitation, soil infiltration and soil water capacity, population and road density, and distance to highways. Because very few human-caused fires were recorded, models were developed and tested for lightning-caused fires over the entire county and in forested areas only. Lightning strike density was the first or second most important predictor of fire occurrence in the entire county and in forested areas. Higher fire density and higher lightning strike density were observed in the eastern half of the county compared to the western half. Overall, the spatial distribution of wildfire occurrence was controlled more by ignition mechanisms than by processes influencing fuel moisture, accumulation, or both.