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.

Engineered loess-filled gullies, which are widely distributed across China's Loess Plateau, face significant stability challenges under extreme rainfall conditions. To elucidate the regulatory mechanisms of antecedent rainfall on the erosion and failure processes of such gullies, this study conducted large-scale flume experiments to reveal their phased erosion mechanisms and hydromechanical responses under different antecedent rainfall durations (10, 20, and 30 min). The results indicate that the erosion process features three prominent phases: initial splash erosion, structural reorganization during the intermission period, and runoff-induced gully erosion. Our critical advancement is the identification of antecedent rainfall duration as the primary pre-regulation factor: short-duration (10-20 min) rainfall predominantly induces surface crack networks during the intermission, whereas long-duration (30 min) rainfall directly triggers substantial holistic collapse. These differentiated structural weakening pathways are governed by the duration of antecedent rainfall and fundamentally control the initiation thresholds, progression rates, and channel morphology of subsequent runoff erosion. The long-duration group demonstrated accelerated erosion rates and greater erosion amounts. Concurrent monitoring demonstrated that transient pulse-like increases in pore-water pressure were strongly coupled with localized instability and gully wall failures, verifying the hydromechanical coupling mechanism during the failure process. These results quantitatively demonstrate the critical modulatory role of antecedent rainfall duration in determining erosion patterns in engineered disturbed loess, transcending the prior understanding that emphasized only the contributions of rainfall intensity or runoff. They offer a direct mechanistic basis for explaining the spatiotemporal heterogeneity of erosion and failure observed in field investigations of the engineered fills. The results directly contribute to risk assessments for land reclamation projects on the Loess Plateau, underscoring the importance of incorporating antecedent rainfall history into stability analyses and drainage designs. This study provides essential scientific evidence for advancing the precision of disaster prediction models and enhancing the efficacy of mitigation strategies.

Rainfall-induced landslides are a frequent and severe natural hazard in the southern regions of Ethiopia. These occurrences substantially threaten the welfare of workers, equipment, and the efficient completion of construction projects. This paper provides an insight into the mechanism and kinematic behavior of rainfall-induced landslides in southern Ethiopia. A comprehensive investigation was carried out on the Jinka landslide, a notable case study in June 2018. The investigation involved Material Point Method numerical simulations, which were informed by extensive geotechnical investigations and laboratory tests. Historical landslide events and rainfall data were also systematically analyzed to establish critical rainfall thresholds for predicting landslide occurrences. It was observed that excess pore water pressure near the sliding surface significantly reduces effective stress, leading to a notable decrease in shear resistance and increased soil mobility. The landslide followed a regressive pattern, initiating from the lower toe, propagating through the middle sections, and ultimately reaching the upper crest. The kinematic parameters of the sliding mass demonstrated varying velocities, with the mass sliding downslope exhibiting a greater velocity than the block positioned above it. The kinematic characteristics indicate that the landslide exhibits distinct movement patterns relative to varying microtopography. Additionally, threshold analysis revealed that the critical rainfall that triggers landslides is the maximum daily rainfall of 44 mm with 30 days antecedent rainfall of 304 mm and the minimum average daily rainfall of 4 mm with 30 days antecedent rainfall of 378 mm. The results indicated that soil saturation from rainfall diminishes strength and increases the acceleration of sliding masses, while antecedent rainfall is pivotal in landslide events. This study can provide a reference for understanding the mechanism of the landslides induced by rainfall and guidelines for future infrastructure planning and early warning systems in the region.