ADVANCING POST-WILDFIRE DEBRIS FLOW MONITORING IN WASHINGTON STATE

Post-wildfire debris flows pose a significant hazard across Washington state, with climate change escalating risks in more densely populated areas. In response, the Washington Geological Survey (WGS) launched a post-wildfire debris flow monitoring initiative covering 11 burned areas since 2022. WGS utilizes various tools to correlate rainfall intensity with debris flow occurrence, including rain gauges, telemetered weather stations, pressure transducers, motion-activated cameras, and field observations. We developed communication tools that increase awareness for at-risk communities and provide real-time access to observations for the public and our partners. Over 50 debris flows and 65 hyperconcentrated flows/flooding events have been recorded since 2022 providing significant insights into rainfall intensity thresholds for debris flows in Washington. Additionally, we have begun estimating debris flow volumes during field assessments, another important facet of understanding these hazards. WGS plans to continue monitoring these areas for several years post-fire to better understand the temporal window of increased debris flow risk. These monitoring efforts deepen our understanding of post-fire debris-flow processes in the pacific northwest, thereby improving hazard assessment models and refining estimates of triggering rainfall thresholds for early warning systems.