Modeling wildfire impact on hydrologic processes using a precipitation-runoff model

Abstract

As large magnitude wildfires persist across the western United States, understanding their impact on hydrologic behavior and predicting regional streamflow response is increasingly important. Peak flows, sediment flows, and debris flows in burned watersheds are often addressed, but wildfires also alter the timing and overall volume of runoff, making the prediction of post-fire streamflow critical for water resources management. Six wildfire-impacted watersheds in the western United States are modeled using the Precipitation Runoff Modeling System (PRMS), a distributed-parameter, physical process based watershed model. Two change detection modeling approaches are applied in order to better understand post-fire changes and their related processes. First, the model is used to determine if each watershed shows significant changes in flow regimes following each wildfire. Second, post-fire parameterization is examined using a generalized likelihood uncertainty estimation (GLUE) approach and a national-scale sensitivity analysis. Three of the six watersheds showed significant increases in the difference between observed and modeled daily streamflow following the wildfire. For these watersheds, the parameterization analysis using PRMS revealed that changes in immediate surface runoff processes are best represented through preferential flow and imperviousness, and changes in evapotranspiration can be best represented through soil zone capacities.