Climatic Context Is Key to Understanding Post-fire Watershed Responses Across the Western United States

Mountain watersheds across the western United States are increasingly impacted by wildfire and declining snowpacks. This study used a large data approach to quantify post-fire changes in streamflow metrics for snow-dominated, rain-dominated, water-limited, and energy-limited watersheds. We found that snow-dominated watersheds exhibit significant post-fire increases in summer low flows and spring peak flows, and an earlier onset of the spring freshet. Rain-dominated watersheds in water-limited climates showed only weak post-fire increases in low flows. Annual streamflow analyses obscured the significant post-fire hydrologic impacts in snowy, energy-limited watersheds. The snow-forcing was even stronger for energy-limited watersheds where burned area exceeded 50%. As climate change causes snowpacks to decline and forest fires to expand into the seasonal snow zone, these post-fire streamflow impacts are likely to become more pronounced and widespread. Recognizing and anticipating differential post-fire hydrologic shifts is critical for effective post-fire water management.