Rain score of heavy rainfall and number of persons suffered death from its disaster

The rain score P was proposed as a new comprehensive term defining the rain strength and utilized for the debris flow occurrence of Mizunashi river, Mt. Unzen. The relation between numbers of human death (d) caused by the heavy rainfall disaster and the rain score is discussed in this report. The second rain score P2 is found as another important factor for human death occurrence. The relation between d and P1,P2 are investigated on the 51 heavy rainfall disasters occurred in years of 1953-1983. P1 and P2 are obtained by the statistical relations between (P1,P2) and (the maximum 1 hour rainfall amount R1mm, the maximum 3 hour rainfall amount R3mm), because only R1,R3 data are referred in the disaster records. Although the multi correlation coefficient of d-(P1,P2) is not so good, the trend of estimated d explains well the characteristics of historical heavy rainfall disasters in Japan. The d estimating equation is used in the 1-3 hour rainfall forecast method in case of Nagasaki event which caused 299 deads during 7 hours (18h00-01h00,Jul. 23,24,1982). The predictions of d at 19h20 and 19h40 in early stage of rainfall was 50 and 150 persons, respectively.