Clustered shallow landslides triggered by heavy rainfall in May 2022 in Wuping County, Fujian Province, China

Abstract

Landslides triggered by extreme rainfall often cause severe casualties and property loss. A recent case in Wuping County, southeastern China, exemplifies this. Between May 22 and 27, 2022, cumulative rainfall exceeded 250 mm, with a peak hourly intensity of 61.2 mm/h, triggering 867 shallow landslides averaging 1.3 m in thickness. The spatial distribution characteristics and initiation mechanism of landslides were revealed through remote sensing analysis, field surveys, and a series of geotechnical tests. Landslides were concentrated on 30°–50° slopes, with convex slopes showing the highest frequency ratio (FR = 1.2). In contrast, landslides were rare in the due north direction, likely due to variations in solar exposure and precipitation patterns. Higher densities occurred along road-cut slopes, emphasizing human engineering influences. Sliding surfaces formed at the residual soil–weathered layer interface, where differences in composition, permeability, and shear strength played a key role. Clay minerals increased self-weight stress post-rainfall, while residual soil cohesion reduced by 36.9% upon saturation, significantly exceeding reductions in the weathered layer. Shallow landslides displayed high mobility, potentially forming landslide–debris flow chains in steep valleys, amplifying hazards. Compared to global extreme rainfall events, Wuping’s rainfall was lower but unprecedented regionally. Analysis of rainfall intensity and threshold models underscores the need for thresholds tailored to local geological conditions and denser rainfall station networks to mitigate landslide risks. This study provides a typical case of shallow landslides in granite areas, offering insights for susceptibility mapping, early warning systems, and disaster chain research.