Proper warning and evacuation are essential for mitigating sediment]related disasters during heavy rainfall. For this purpose, a scientific and rational rainfall index should be established in accordance with regional geological and topographical characteristics. The authors proposed Rainfall index RŒ for warning against sediment]related disaster. It became possible to express influences of both preceding and present rainfall by a single value of RŒ. This rainfall index was developed by using the past disaster cases in Masado (decomposed granite soil) area in Hiroshima district. In this paper, several cases of slope failure and debris flow including non]granite zone in 2005 were also examined to confirm the effectiveness of this newly]proposed rainfall index. It has been understood that the rainfall index RŒ will be able to use widely, if the coefficient and the reference value are chosen properly for each region considering its geological and topographical characteristics. Also, in this paper, we proposed the method for easily converting the usual rainfall index into the RŒ.
Key wordsFrainfall index RŒ, sediment]related disaster, regional characteristics, method for warning