A Modeling Framework to Characterize Post-Fire Watershed Risk and Inform Immediate Response

Severe wildfires can alter every aspect of a watershed from vegetation and soils to hydrology and water quality. As severe wildfires increase in both size and frequency, land managers are faced with increasingly complex decisions about where to focus immediate watershed response given limited resources. We present a post-fire watershed risk framework that builds upon the commonly used quantitative wildfire risk assessment by combining observed fire behavior with an effects analysis that models post-fire erosion, sediment transport to water supplies, and debris flows. BARC burn severity is used to modify the cover and soil erodibility factors in the Revised Universal Soil Loss Equation and calculate burn extent and severity for the USGS debris flow model. We also integrate an optimization module that considers the feasibility, cost, and potential erosion reductions of aerial mulching to design a post-fire treatment plan that maximizes sediment reductions per dollar spent. Model output can help land managers' target strategic locations for immediate response and provide cost and feasibility estimates to assist with funding and policy discussions. We present this framework in a case study focused on the 2020 wildfires in Colorado, though this framework could be applied broadly.