Assessing Flood Risk During Extreme Rainfall Events: Case Studies from Recent Events in Japan

In recent years, Japan has experienced a notable increase in extreme rainfall events, which have frequently triggered severe flooding, resulting in significant loss of life and property damage. Consequently, the overall cost of flood-related disasters has continued to rise. Climate change projections indicate that the frequency and intensity of such extreme events are likely to increase in the future.
With advancements in observational technologies, high-resolution radar-based rainfall data are now available in near real-time across Japan, providing valuable input for flood risk assessment. In this study, we rapidly developed a flood risk mapping framework using a combination of radar rainfall data, hydrological data, historical rainfall records, and various physiographic factors. The risk assessment was conducted using a Geographic Information System (GIS)-based Analytic Hierarchy Process (AHP) approach, focusing on past extreme events.
Our analysis produced several risk maps, including real-time hydrological hotspot maps and overall flood susceptibility maps for specific extreme rainfall events. To validate our results, we compared them with observed flood damage data and insurance claim records. The comparison showed promising agreement, suggesting the reliability of our approach. However, further refinement is necessary to enhance the robustness and predictive capability of the method. We believe the proposed methodology offers a valuable tool for flood disaster risk management and can support decision-making for stakeholders preparing for future extreme flood events.