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.
|Title||The rainfall intensity-duration control of debris flows after wildfire|
|Authors||Matthew A. Thomas, Donald N. Lindsay, David B. Cavagnaro, Jason W. Kean, Scott W. McCoy, Andrew Paul Graber|
|Publication Subtype||Journal Article|
|Series Title||Geophysical Research Letters|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Geologic Hazards Science Center|