(6)

On July 20, 2024, a rainfall-induced, group-occurring debris flow event occurred in the Malie Valley, southwestern China. This study systematically investigated the damage and rainfall-triggering conditions of the debris flow event using remote sensing data, field surveys, and satellite-based rainfall measurements. Debris flows were commonly initiated by mobilizing widespread shallow landslides on steep slopes. Among them, the Lannisanwan (LNSW) debris flow was the most extensive and destructive, and its impact was amplified due to several factors, such as steep terrain gradient, high channel sinuosity index, and significant accumulation of loose material. The LNSW debris flow reached a velocity of 5.29 m/s and a peak discharge of 2,304.30 m3/s at the catchment outlet. Furthermore, the convergence of debris flows from tributaries exacerbated the hazards alongside the main valley channel. Though the event was triggered by the short-duration night rainfall, with a peak intensity of 25.44 mm/h, antecedent rainfall played a critical role. Rainfall analysis revealed that the 3-day antecedent effective rainfall total was as high as 108.75 mm, 4 to 20 times greater than those of past heavy rainfall events in the area. This study emphasizes the importance of antecedent rainfall preceding intense rainfall on landslide-type debris flows and highlights the aggravating effects of group-occurring and night-occurring on the magnitude and consequences of debris flows.

来源平台：LANDSLIDES