16-5 Lessons Learned from Three Pre-wildfire Assessments of Postfire Flow Hazards in Arizona

Session: Wildland Fire: An Agent of Geomorphic, Ecologic, and Societal Change

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Since 2015, the Arizona Geological Survey and JE Fuller Hydrology and Geomorphology, Inc. have conducted pre-wildfire assessments of potential postfire debris-flow and flood hazards in three Arizona counties: Coconino (completed in 2017), Yavapai (2024), and Gila (ongoing). We begin with a high-level, county-wide assessment to identify areas with higher potential for wildfire and postfire flows that could impact the built environment. Then we assess the scale of the risk to the built environment and use that to determine areas of highest concern in the county. The county then selects two of those areas for detailed modeling to better identify risks and mitigation opportunities. Through modeling reasonable scenario wildfires and the respective soil burn severity, we can compare the changes in flood flows between the pre- and post-fire conditions in 10- and 100-year, 6-hour or 24-hour rainfall events. Furthermore, we can estimate the increase in the debris-flow likelihood and volume potential for the 1-, 2-, and 5-year storm event in post-fire conditions. These results help communities to identify their existing vulnerabilities and inform future project planning, mitigation efforts, and infrastructure improvements as is appropriate to each county’s specific needs before a fire breaks out. For example, we may focus on assessing forest treatments to mitigate risks in one county while identifying infrastructure needs in another county. In addition to discussing our methods and the challenges we have encountered, we’ll also present lessons learned that can help inform future pre-fire flow hazard assessments.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7916

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