RAPID: Land surface hazards under accelerating climate change: Example from 2023 Hurricane Hilary

The climate impact on solid earth hazards, such as landslides, debris flows, river aggregation and flooding, has historically received little attention, but in recent years, this impact is disrupting communities and altering the environment we live in. There is an urgent need to understand how new climate regimes are generating storms that unleash unprecedented episodes of erosion, ground failure and deposition.

For example, arid environments are shaped by long periods of slow geomorphic activity, punctuated by major events that can transform landscapes in a geological instant. These events, often triggered by major storms, also present a range of hazards, including floods, landslides, and debris flows that can damage major infrastructure (e.g., roads, buildings) as well as natural and cultural heritage sites.

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 County. 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 major 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.

Collection of perishable field data is the main goal of this award, to gain insights into the debris flow observations that enable longer term predictions of the hazard cascade. Such direct observations that can test models and drive new understanding of land surface hazards are sparse in part because major landscape-changing events, although potentially catastrophic, are rare and thus few natural examples are well documented using modern technologies.

Technologies like Light Detection and Ranging (LiDAR, or laser scanning) and Structure-from-Motion (SfM) enable change detection and quantification that provide previously elusive insights. Such data include detailed records of land surface change, the properties of ground materials that were eroded and redeposited, and impact on infrastructure. The research will be conducted within the structure of the Center for Land Surface Hazards (CLaSH), thereby supporting community building initiative and engaging researchers across disciplines in hazard-related science, by including new researchers, and students who were 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 to empirically understand the impact of Hurricane Hilary on the geologic environment, but also guide next-generation hazard cascade models that can be validated against the field data collected from this project.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.