An Analysis of The 9 January 2018 Montecito, California Post-Fire Runoff Event Using Gssha Hydrological Model

Inundation models that realistically simulate hydrologic processes are in demand for post-wildfire flood susceptible regions like Southern California where precipitation occurrences, increasing population densities, fire-prone vegetation, and steep terrain combined with wildfires, trigger flooding events. In Santa Barbara and Ventura Counties following the 2017 Thomas Fire, on January 9th, 2018, an intense atmospheric river flood resulted in a series of destructive water and debris flows causing major damage to life and property. This study utilizes the physics-based Gridded Surface Subsurface Hydrological Analysis, GSSHA, a watershed numerical model to simulate the flood events in the San Ysidro and Montecito watersheds. To assist in reducing uncertainties affecting model predictions, a parametric sensitivity analysis of the post-fire runoff process is applied using the “Shuffled Complex Evolution”, SCE optimization algorithm. Understanding post-fire hydrologic processes and improvements in modeling is crucial in providing a framework for emergency assessments and therefore potentially reduce the impacts of post fire flooding on landscapes, infrastructure (e.g., roads, reservoirs), and communities.