気候変動を考慮した流域全体を俯瞰した水害リスクの考え方

抄録

The frequency of extreme rainfall and flooding events has increased over Japan in recent years. With the need to account for the change in the frequency of extreme rainfall, Japan’s new flood control policy, which aims to increase the resilience and sustainability of river basin disasters through comprehensive multilayered actions, considers river basins to include watersheds and floodplain areas. In this study, we propose the risk assessment as an amalgamation of two different approaches, i.e., physical model-oriented ensemble projection and pure mathematical statistics, since both approaches have been found to show similarity in the annual maximum rainfall and the range of its uncertainty. The study also introduces the F-N curve, which shows the increased frequency of rainfall events in the future climate that causes the same number of fatalities when compared to the past climate. Lastly, an analogy has been drawn between modern portfolio theory and flood risk assessment, to facilitate budget allocation to the most resilient flood control measure based on the thousands of rainfall patterns generated from the ensemble approach.