Abstract
The present study discusses the relationship among rainfall, geology characteristics and debris flow occurrence using effective rainfall and rainfall index R', which expressed rainfall history by one value that combines long-term effective rainfall Rw and short-term effective rainfall rw. Three debris flow disasters in Osumi district, Nagiso-town and Hiroshima-city are chosen for investigation. We found examples in which the occurrence time of the debris flow was different, even when the disaster spots are in the same rain gauge station area, because R' is only determined by rainfall, which is the inducing factor of debris flow occurrence. We also scrutinized the geology of the disaster source points and found that many debris flows occurred in the distribution of volcanic sediment, the sedimentary rock of the accretionary complex, and granite.
