Arizona Geological Society: Postfire Debris-Flow Research at the Arizona Geological Survey Efforts to Improve Hazard Assessments and Mitigation Options

In Arizona, and across the western US, wildfires have increased in size and severity and, due to invasive vegetation and drought, have encroached into ecosystems that historically did not sustain large, high severity fires (e.g., the Sonoran Desert, the Pacific NW).  Concurrent, increased development into the wildland-urban interface (WUI), where the built and natural environments intermingle, has placed more people at risk from wildfires and from postfire floods and debris flows. Wildfires consume vegetation and alter soil hydrologic properties, increasing runoff, erosion and the susceptibility of burned watersheds to postfire floods and debris flows. Postfire debris flows in Arizona are typically triggered by short-duration, high-intensity convective rainfall during monsoon storms. Because the monsoon season (June 15 – September 30) immediately follows peak fire season (April – June), there is little time following a fire for communities to mitigate the risks from post-fire floods and debris flows.

In this talk, we’ll first discuss how wildfires impact the landscape to increase the likelihood of postfire debris flows and floods, the transient nature of fire impacts on the landscape, the challenges of mitigating these hazards in areas where fire season and monsoon overlap, and projects the AZGS and Geosciences are conducting to address these issues.  We’ll close with an ongoing case study assessing the effectiveness of novel mitigation strategies deployed in northern Arizona.

Presented by

Ann Youberg (l) Senior Research Scientist

and Rebecca Beers (r) Research Scientist