2019 CSDMS meeting-107
Modeling the hydrology of a post-fire landslide: Case study of the Thomas Fire, CA
Post-wildfire debris flows are a major source of geomorphic change that by nature of the large amounts of mass they mobilize can be deadly and destructive. These landslides are triggered by the interaction of fire-induced changes to both hydrologic and geomorphic responses. Representing the cascading effects of fire on landslides requires linking information from hydrologic models and debris flow models and presents both technical and theoretical challenges. Statistical models of debris flows have been used successfully for decades to assist in disaster prevention and mitigation. However, physically-based models that may provide additional insight into underlying processes and behavior under extreme conditions are rarely used. We present a case study to begin addressing these challenges, focusing on a basin burned by the Thomas Fire in southern California in 2017. Soil water content maps and sediment fluxes produced by the Distributed Hydrology Soil Vegetation Model (DHSVM) in areas at risk for debris flows are compared with times and locations of known landslides. The degree of correspondence between modelled debris flow risk factors is compared for different potential methods of representing fire in DHSVM, including: changes to soil depth, soil infiltration characteristics, vegetation cover, and vegetation properties. Finally, future challenges of linking information across hydrologic and landslide models are discussed, towards more accurately representation of the spectrum of debris flow processes.