Thomas C. Harmon1,2,3, Humberto Flores3, Lorenzo Booth4, Emily R. Waring2,Emily Gomez1, and Stefano Carpin4,51Department of Civil & Environmental Engineering, University of California Merced2Sierra Nevada Research Institute, University of California Merced3Enivronmental Systems Graduate Program4Electrical Engineering & Computer Science Graduate Program, University of California Merced5Department of Computer Science, University of California MercedPoster presentation GC51P-0859 at the Fall 2023 Meeting of the American Geophysical Union, San Francisco, CA, December 12-16, 2023

Coastal watersheds impacted by wildfires experience increased sediment delivery to the ocean that alter the availability of limiting factors (i.e., light) for marine organisms. With increasing wildfire magnitude and severity, it is critical to explore changes in riverine discharges to the ocean to assess cascading hazards associated with wildfires. In situ data and a hydrological model adapted to capture fire-related land use change are paired with remotely sensed turbidity data to investigate Woolsey Fire impacts on Malibu Creek, California, USA. Maximum post-fire observed and simulated discharges and sediment loads were between 1.4 – 4.8 and 0.93 – 13.9 times higher, respectively, than during non-fire periods with similar rainfall. Mean turbidity also increased to 18.2 Formazin Nephelometric Unit (FNU) during the first storm post-fire (mean background value of 4.3 FNU). Synergies between the methods were able to better characterize post-fire sediment fluxes versus a single method. Notably, remote sensing observations captured rapid coastal sediment exports within the first post-fire month that SWAT did not. Conversely, sporadic remote sensing observations did not reflect ongoing post-fire sediment erosion (largely due to cloud cover issues), which SWAT did demonstrate. These data are essential to understanding fire-related marine ecological changes and implementing effective management and conservation initiatives.