The August 2023 Hurricane Hilary was a Category 4 Pacific hurricane that triggered an unprecedented tropical storm warning for Southern California, extending from the Mexico-US border to regions north and east of Los Angeles. Unlike most of the wintertime precipitation that arrives in this region in narrow, concentrated bands, Hurricane Hilary distributed heavy rainfall across a wide swath of southern California, providing an opportunity to study the widespread geomorphic and societal impact of a rare precipitation event. The most severely affected regions have been the normally arid desert regions, which suffered heavy rainfall in excess of typical annual totals with triggered debris flows, flash flooding and sediment debris waves. This event gave the Clash team an opportunity to pivot the scenario planning exercise onto a real event. During the final day of the Jackson Community Meeting (and while the storm was starting to impact southern California in real time!) the group engaged in a pre-event planning session focused on rapid deployments and collection of perishable data that addresses the hazard cascade. Over the following week, the PI team developed and were subsequently awarded a NSF-RAPID proposal. The field work took place in November and was concentrated in the Death Valley area and burn areas of the San Gabriel/ San Bernardino Mountains. Broader impacts include improved land surface hazards models, understanding of the impact of precipitation-triggered debris flows on infrastructure, and training of students in field data planning and acquisition following disasters. Graduate students from multiple institutions and at varying career stages led the field component including data collection, providing in-practice opportunities for mentoring and cohort building. The research will be conducted by the Center for Land Surface Hazards (CLaSH) team, thereby supporting a community building initiative and engaging researchers across disciplines in hazard-related science, by including new researchers not previously involved in CLaSH. Data generated from this research will be made publicly available via open access repositories, enabling use by the wider research community.
