A case study of shallow landslides triggered by rainfall in Sanming, Fujian Province, China

Two heavy rainfall events occurred in Sanming City in Fujian Province, China, on May 16 and June 10, 2019. Many small-scale, shallow earthen landslides were triggered by these two rainfall events. Aerial photographic interpretation and field investigations were conducted to identify the shallow landslides characteristics. A total of 150 shallow landslides were investigated during the field survey, and a total of 28 shallow landslides were studied using aerial photographic interpretation. The total number of shallow landslides was 178. We analyzed the characteristics of these shallow landslides, such as the thickness, area, volume, plan curvature, profile curvature, slope angle, lithology, elevation, and vegetation. The survey results showed that more than half of the shallow landslides (103 out of 178, 57.9%) were along the roads and the urban greenway, showing the characteristics of development along the engineering activities. We also tested a model of the probability thresholds for the occurrence of shallow landslides. Four classes regarding the probability and frequency of shallow landslides were identified by the model. The warming levels were defined as “Null” (below 5%), “Watch” (5–20%), “Attention” (20–50%), and “Alarm” (above 50%). The probability and frequency of shallow landslides increase as the thresholds increase, which is expressed through a percentage. The rainfall thresholds of the model describing the probability of the occurrence of shallow earthen landslides may decrease when the triggering event is fairly closely preceded by another heavy rainfall.