Method to Develop Critical Rainfall Conditions for Occurrences of Sediment-Induced Disasters and to Identify Areas Prone to Landslides

The present study demonstrates a method to specify critical rainfall conditions for the occurrence of a sediment disaster and identify areas prone to landslides using a simulator proposed by the current authors for sediment hazards. The simulator predicts spatial and temporal distributions for surface and subsurface flows, landslides, and debris flow resulting from rainfall events. The method to develop a critical curve for the occurrence of a disaster is proposed using simulated landslide data derived from artificially specified rainfall conditions, past rainfall data, and disaster records. Usually, a rainfall event also constitutes a period without rain, and this method can be used to evaluate the influence of the no-rain period. In addition, we propose a method to classify slopes according to the probability of landslide occurrences on a domain defined by slope gradient versus catchment area, using data on landslides resulting from a specified rainfall amount and intensity. Areas identified as having a high probability of landslide occurrences correspond to the runout mark of landslides and debris flow in August 2014.