FLOOD RISK PROBABILITY PREDICTION USING A RAINFALL INDEX EQUIVALENT WARNING LEVEL 4 FOR EACH RIVER SYSTEM

Abstract

 It is necessary to develop a rainfall index that directly predict the occurrence of flooding for early evacuation of the residents. In this study, we proposed a method to directly and probabilistically predict the occurrence of inundation from a rainfall index. We calculated the 24hours rainfall averaged over the catchment area (Lv4 rainfall) corresponding to the hazardous water level at each 109 class A river systems nationwide based on past observed data of rainfall and water level. Then, we evaluate the flood risk probability that the water level reach the hazardous level, by using the Lv4 rainfall and an ensemble predicted rainfall data. This method was applied to the heavy rainfall events in July 2020 at the Kyushu region. The results indicated that the rates of concordance, oversight and missing were 27.8, 0.76 and 5.46%. The median of lead time was 19 hours. These show the fundamental validity of this method.