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Pre-fire assessment of post-fire debris flow hazards in the Santa Fe Municipal Watershed

Manuel Lopez, Ellis Margolis, Ann Tillery, Steven Bassett , Alan Hook

Abstract

Background: Wildfires are increasing in size and severity due to climate change combined with overstocked forests. Fire increases the likelihood of debris flows, posing significant threats to life, property, and water supplies. Aims: We conduct a debris-flow hazard assessment of the Santa Fe Municipal Watershed (SFMW) to answer two questions: where are debris flows most likely to occur and how much debris might they produce? We also document the influence of fuels treatments on fire severity and debris flows. Methods: We model post-fire debris-flow likelihood and volume in 103 sub-basins for 2-year, 5-year, and Probable Maximum Precipitation rainfalls following modeled low-, moderate-, and high-severity wildfires. Key Results: Post-fire debris-flow likelihoods were > 90% in all but the lowest fire and rain scenarios. Sub-basins with fuels treatments had the lowest burn severities, debris-flow likelihoods, and sediment volumes, but treatment effects decreased with increased fire severity and rain intensity. Conclusions: Post-fire debris flows with varying debris volumes are likely to occur following wildfire in the SFMW, but fuel treatments can reduce likelihood and volume. Implications: Future post-fire debris flows will continue to threaten water supplies, but fuel reduction treatments and debris-flow mitigation provide opportunities to minimize effects.

WF23065  Accepted 19 May 2024

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