Growing Impact of Wildfire on Western US Water Supply
This study analyzed 72 forested basins across the western US that burned between 1984 and 2019 and showed the multi-basin mean streamflow was significantly elevated for an average of 6 water years postfire, compared to the range of results expected from climate alone. Researchers found that the streamflow response scales with fire extent: among the 29 basins where >20% of forest area burned in a year, streamflow over the first 6 water years postfire increased by 30%. Postfire streamflow increases were significant in all four seasons.
Historical fire-climate relationships combined with climate model projections suggest that 2021 to 2050 will see repeated years when the climate is more fire-conducive than in 2020, the year currently holding the modern record for forest area burned in the western US. The results suggest that burned areas will grow enough over the next 3 decades to enhance streamflow at regional scales.
Wildfire is an emerging driver of runoff change that will increasingly alter climate impacts on water supplies and runoff-related risks. Streamflow often increases after fires, but the persistence of this effect and its importance to present and future regional water resources are unclear. Researchers address this knowledge gap in the western United States, where annual forest fire areas increased by more than 1,100% from 1984 to 2020.