Evaluating post-fire watershed response to varying burn severity and precipitation regimes using fully-distributed and integrated hydrologic models

Wildfires can cause substantial changes in vegetation and soil, affecting water cycling within ecosystems. This study uses the Advanced Terrestrial Simulator (ATS), an integrated and fully distributed hydrologic model at the watershed scale, to examine post-fire hydrologic responses in watersheds with varying burn severities in the Pacific Northwest region of the United States. The model integrates surface overland flow, groundwater flow, and canopy biophysical processes. We developed a new fire module in ATS to account for changes in soil hydraulic properties caused by fire in the topsoil layer. Modeling results show that, in the year following a high-severity burn, watershed-averaged evapotranspiration decreases by about 25%. Post-fire peak flows increase by 18%–29% in watersheds affected by moderate to high burn severity, while low-severity burns produce almost no change in peak flows. High-severity fires also reduce infiltration rates within the affected watershed during the first post-fire wet season. Numerical experiments with varying precipitation regimes after a high-severity burn indicate that peak flows can rise by as much as 29%. These findings underscore the importance of using fully distributed hydrologic models to quantify hydrologic disturbance–feedback loops.