Dynamics and Perceptions of Ultrahazardous Flooding across the Wildland Urban Interface

This project explores post-wildfire flooding risks facing communities and neighborhoods that have developed at the base and long the slopes of mountains in the western United States. These kinds of developments have and continue to expand throughout the southwestern and western United States as urban and suburban areas move into wildland areas. Post-wildfire flooding can be ultrahazardous due to its rapid-onset, high-velocity, and erosive potential, leading to debris-laden flows with unpredictable paths.

This project will advance understanding of these flood risks, and opportunities for increased flood resilience, considering three interwoven elements: environmental hazards (wildfire, mud/debris, and flooding), the built environment (stormwater infrastructure), and human populations. Working with environmental and socio-economic data from across Riverside County, California – part of the Los Angeles Metropolitan Region– innovative models that integrate the effects of fire, debris basins, and flood control channels on flood and debris hazards will be co-developed with community partners and applied to estimate how exposure varies spatially and over time.

Hazard estimates will be combined with household survey data capturing hazard awareness, perceptions, and preparedness to characterize variations in risks and risk perception across the area’s diverse socioeconomic population. This research supports NSF's mission to promote the progress of science and to advance our national welfare by generating both tools and insights to improve flood risk awareness and preparedness, which will save lives, reduce economic losses in future events, and enhance community resilience.

Climate change and urban expansion are leading to an escalation of flood and debris risks. Global warming is resulting in more intense and frequent wildfire during Summer and Fall and more intense precipitation in Winter and Spring. Furthermore, awareness and preparedness for flooding is hypothesized to be especially low among residents, particularly because the arid southwest is known for “unpredictable flow path flooding” that occurs after flood controls system are clogged with debris and/or overtopped.

This project will advance an innovative stochastic modeling framework for estimating present and future flood and debris hazards facing development – a systematic approach for capturing the uncertainty in rainfall patterns, wildfires, the performance of flood control infrastructure, and climate change. Furthermore, the spatial distribution of hazards will be mapped using fine-resolution flood hazard models and intersected with socioeconomic data and indicators of vulnerability drawn from a household survey of flood awareness and preparedness, yielding important new insights into risks and risk perceptions.

Finally, the research team will partner with public works and emergency management personnel from local and state government to co-develop data products and tools for flood risk management, and to make these tools widely available for post-wildfire flood risk management. Publications, software, and data derivatives generated during this project will be made available on the project website, GitHub and public data repositories.

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.