GIS Modeling to Assess Economic Risk from Post-Fire Debris-Flows

Post-fire debris-flows are a serious hazard in the western United States. Potential impacts of these events include loss of human life, destruction of structures, and degradation of habitat and water quality. While loss of human life is the most important concern in a geohazard assessment, potential loss of life is extremely difficult to quantify and is beyond the scope of this paper. This paper focuses instead on the analysis of economic risk from post-fire debris-flows in support of cost-optimized post-fire debris-flow hazard management strategies. Common approaches to evaluating post-fire debris-flow hazards provide either qualitative estimates of inundation zones or no inundation estimates at all. Quantitative estimates of debris-flow damage and economic risk support the selection of natural hazard management strategies following a fire via optimization approaches. The first step in this process is an analysis of damage cost estimates and related probabilities. Debris-flow hazards and associated damage costs for individual drainages can be analyzed in ArcGIS utilizing existing models and readily available GIS data. Preliminary case study results suggest that this process can be used to identify the most economically concerning drainages. These results can guide allocation of emergency management funds and optimization of debris-flow management strategies following a wildfire. This paper discusses where to acquire geologic and social input data and how to operate the GIS models in support of the post-fire debris-flow economic risk assessment. A case study from southern California is provided to illustrate the methods.