Extreme rainfall and the initiation of debris flows: Insights from the Shuikouyangou case in Sichuan, China

Abstract In the context of climate change, the increasing frequency of extreme rainstorms has led to the emergence of debris flow hazards in catchments with no prior history of such events. This phenomenon presents a growing challenge for debris flow risk assessment and mitigation. The Shuikouyangou debris flow in Sichuan Province, China, triggered by record‐breaking rainfall, occurred in a previously unrecognised debris flow‐prone watershed. To investigate the triggering mechanisms, we conducted field surveys, analysed rainfall infiltration responses and performed hydrological simulations focused on runoff generation dynamics. Results indicate that newly initiated debris flows under extreme rainfall conditions are closely associated with short‐duration, high‐intensity runoff. Such runoff rapidly concentrates and exerts strong erosive forces, ultimately mobilising loose surface materials and initiating debris flows. A conceptual model of runoff‐induced debris‐flow mechanisms was presented. This study enhances our understanding of how extreme precipitation can trigger debris flows in previously unaffected basins and provides critical insights for developing science‐based mitigation strategies in the face of increasingly frequent extreme weather events.