Hydrological benefits of restoring wildfire regimes in the Sierra Nevada persist in a warming climate

Abstract

Reducing the risk of wildfire and increasing the security of water supply from mountain catchments are both urgent priorities in the Western US. These goals may be synergistic, thanks to the reductions in transpiration and fire hazard associated with reducing forest cover. Data and modeling efforts based on the Illilouette Creek Basin (ICB) in Yosemite National Park, where fire use policies have been implemented to restore wildfire since 1972, suggest that these policies reduced fire hazards and increased annual streamflow production through large changes to landscape-scale forest cover and structure. Expanding fire use strategies through the Western US, however, would mean that any such changes in forest cover and structure would occur in the middle of the 21st century, under different fire frequency and climate conditions than experienced in the ICB to date. It is therefore important to understand if hydrological benefits of fire use are sensitive to anticipated changes in climate and fire frequency. Here, we force an ecohydrological model previously developed for the ICB with an ensemble of downscaled future climate predictions to assess the impacts of climate change and fire use strategies on the hydrology of the ICB. We find that the hydrological impacts of fire use are comparable under observed climate and projected future climates, and are largely insensitive to the significant uncertainties regarding post-fire successional trajectories for vegetation. While expected increases in fire frequency cause minor changes in the basin hydrology, the main impact of more frequent fires is to cause the basin to reach peak hydrological change more rapidly.