The rainfall intensity-duration control of debris flows after wildfire

Matthew A. Thomas; Donald N. Lindsay; David B. Cavagnaro; Jason W. Kean; Scott W. McCoy; Andrew Paul Graber

doi:10.1029/2023gl103645

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The rainfall intensity-duration control of debris flows after wildfire

Matthew A. Thomas·Donald N. Lindsay·David B. Cavagnaro·Jason W. Kean·Scott W. McCoy·Andrew Paul Graber

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Abstract

Increased wildfire activity in the western United States has exposed regional gaps in our understanding of postfire debris-flow generation. To address this problem, we characterized flows in an unstudied area to test the rainfall intensity-duration control of the hazard. Our rainfall measurements and field observations from the northern Sierra Nevada (California, USA) show that debris flows resulted from a short burst rainfall during a low-accumulation storm. In contrast, a much higher accumulation storm (∼10 times more rainfall) with lower short-duration rainfall rates only produced low-hazard flooding. We conclude that total storm rainfall is not an ideal metric for identifying the rainfall conditions that initiate runoff-generated debris flows in the first year after wildfire. Rather, a focus on short-duration (<1 hr), high-intensity rainfall that can occur during localized thunderstorms, or bands of intense rainfall during prolonged rainstorms, is more beneficial for the purposes of hazard assessment and warning.

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Geophysical Research Letters Article

Source-reported bounding extent: 39.9333° to 40° latitude; -121.316667° to -121° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Matthew A. Thomas, Donald N. Lindsay, David B. Cavagnaro, Jason W. Kean, Scott W. McCoy, Andrew Paul Graber. 2023-05-23. The rainfall intensity-duration control of debris flows after wildfire. https://doi.org/10.1029/2023gl103645

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