QUANTIFYING IMPACTS OF FIRE-FLOOD CYCLES ON HUMAN AND ECOLOGICAL COMMUNITIES: CASE STUDIES FROM THE CENTRAL COAST OF CALIFORNIA (Invited Presentation)

Climate change is an important driver of fire regime intensification in regions such as the central coast ranges of California, leading to novel increases in fire and post-fire geomorphic disturbances. This necessitates the need to understand how these increases in postfire disturbance will impact sensitive coastal habitats and human communities not accustomed to large and severe wildfire. An opportunity to study this emerged with the 2020 CZU Lightning Complex Fire in the Santa Cruz Mountains that burned ~86,000 acres across redwood forest watersheds which host sensitive riverine and estuarine habitat for endangered anadromous fishes. Currently, there is a paucity of studies on the impacts of post-fire runoff on bar-built estuaries along the west coast of the US. A study was established to use sediment tiles, RTK-GPS, and bathymetric surveying to quantify geomorphic changes to the Scott Creek estuary near Santa Cruz, CA for 3 years in response to post-fire runoff and recent atmospheric river events. Initial results show estuary-wide accretion rates during this post-fire period are ~2-5x higher than longer-term rates spanning ~2 ka prior to Euro-American colonization.

Not only is it important to understand contemporary fire and its current impacts on watershed hazards, but possible future scenarios of fire-flood cycles to allow for longer-term hazard mitigation and fuels management. I will also discuss a pre-fire modeling study that aims to predict future scenarios of soil burn severity and associated debris flow susceptibility further south in the Carmel River watershed. This watershed also hosts endangered aquatic biota as well as significant water supply infrastructure and development intermixed with flammable vegetation and hillslopes prone to mass wasting. This study aims to build on previous work done in southern California to quantify long-term post-fire risks but in a watershed spanning significant gradients in hydroclimate and vegetation communities. These studies provide key opportunities to better understand the hydrogeomorphic impacts of novel increases in fire-flood disturbances.