Analysis of antecedent and real-time rainfall characteristics of a large-scale debris flow event in Southwest China in 2024

On July 20, 2024, a catastrophic group-occurring debris flow event occurred in the Malie Valley, southwestern China, involving nine debris flows primarily initiated by widespread shallow landslides. The event was triggered by a short-duration nighttime rainfall. The triggering rainfall intensity was 25.44 mm/h, and the Malie Valley was nearly at the center of the rainstorm. Since 2000, four historical rainfall events in the region have exceeded this intensity, yet none resulted in debris flows. The total daily rainfall during the event was 100.5 mm, corresponding to only 20-year return period. While differences in long-term antecedent effective rainfall (AER) between this event and previous heavy rainfall events were small, the 3-day AER reached 108.75 mm, which was 4 to 20 times greater than that of earlier events. These findings underscore the critical influence of short-term AER preceding intense rainfall in triggering group-occurring debris flows.