Evaluating how climate-induced changes in wildfire regimes affect forest hydrology in the Sierra Nevada

Abstract:

Climate change is affecting two of the biggest forest management issues facing California in the 21^st century, wildfire and water resources. Yet despite wildfire and water resource issues being intertwined, most studies of the hydrologic response to wildfire has been at the scale of individual wildfire events and do not account for climate impacts on wildfire regimes, which can affect patterns of ignition, seasonality, frequency, intensity, severity, and extent of wildfires. Effective management of water supplies necessitates understanding how changes in these wildfire variables may affect hydrologic variables such as streamflow. In this study, we use a recently developed coupled ecohydrologic-fire model, RHESSys-WMFire, to examine how climate-induced changes in wildfire regimes may alter forest hydrology in the southern Sierra Nevada, California, USA. We present findings comparing simulations with fire exclusion to simulations with a natural fire regime, both with and without climate change, in a factorial design. We evaluate the relative influence of climate change and wildfire on multiple hydrologic variables, including snowpack, evapotranspiration, and streamflow. The results begin to disentangle the complex relationships between hydrologic response to climate change and wildfire, with an explicit focus on the feedbacks between fire frequency, fire severity, and vegetation regrowth.