Understanding the impacts of wildfires on water supply in California

Abstract:

In recent years, wildfires in the western United States have occurred with increasing frequency and scale due to prolonged periods of droughts and increasing temperatures. The majority of these wildfires occurred in forested mountainous watersheds such as the Sierra Nevada Mountains in California, which provide up to 70% of water resources in the state. Despite their significant impacts on redefining landscapes, wildfire effects on watershed scale-hydrology are still highly uncertain. Due to the strong linearities governing the interactions and changes in landscape/vegetation and hydrology, understanding these impacts requires high-resolution physically-based integrated hydrologic models, which solve the transfer and movement of water and energy from the subsurface to the lower atmosphere. We use these models to study the impacts of wildfires on the integrated hydrology in a representative Californian watershed, the Cosumnes River. Results show counterintuitive feedbacks that occur following a wildfire and allow us to identify the regions most sensitive to wildfires’ conditions, as well as the hydrologic processes that are most affected. For example, while evapotranspiration generally decreases in the post-fire simulations, some regions experience an increase due to changes in soil moisture patterns in and near burn scars. Snowpack increases in post-fire conditions, which leads to an increase in summer runoff and groundwater storage.