Abstract
Abstract
Wet to dry climate extremes in California have directly or indirectly impacted droughts, wildfires, and floods resulting in costly damage. Reservoirs in California were built to store snowpack into the summer and provide multiple benefits in the state: they offer municipal and agricultural water resources during the dry season and prevent flooding downstream. The upper Feather River watershed, which drains 9,300 square kilometers (km2) into Lake Oroville, provides water to over 27 million people and 3,000 km2 of farmland. The North Complex fire in 2020 and Dixie and Sugar fires in 2021 burned over 50% of the watershed and their long-term impact on the upper Feather River water supply was previously unknown. This study quantified post-wildfire (postfire) changes in plant water use, soil moisture, and streamflow due to changes in vegetation using a physically-based water balance model. Long term trends revealed decreases in annual precipitation and mid to high elevation snowpack in this watershed from 1981-2020. Due to changes in vegetation, annual postfire streamflow at Feather River at Oroville increased by 22%, 32% and 16% while summer baseflows increased by 5%, 12% and 2% in water years 2022 through 2024, respectively. Larger increases in streamflow occurred during water year 2023, an extreme wet year relative to the other years, highlighting the challenges in quantifying and managing hydrologic systems with naturally high interannual variability. Seasonal soil moisture increased by up to 34% depending on the location, predominantly in fall and summer postfire. Despite observed historical decreases in precipitation and snowpack, changes in vegetation due to wildfires or other disturbances may increase water availability, and continued management of mixed-conifer forests (i.e. thinning and controlled burns) may help offset future reduced precipitation and snowpack and therefore increase water supply resilience.