Simulation-based assessment of inundation risk potential considering the nonstationarity of extreme flood events under climate change

Abstract

The projected increase in the frequency of extreme rainfall events with climate change has serious implications for flood risk management. This study developed a novel method to evaluate future flood inundation risk in the Kakehashi River basin, Japan. First, a pseudo global warming (PGW) method and ensemble simulation techniques were combined to develop rainfall projections with different return periods, based on the Weather Research and Forecasting (WRF) model. Second, runoff analyses were performed for the target river basin, and inundation simulations, including levee breaches, were conducted at high spatial resolution (40 × 40 m). Finally, the potential inundation risk for the river basin was estimated. Rainfall simulation results indicated intensification of short-duration heavy rainfall events. The PGW ensemble simulations indicated that extreme rainfall scenarios with long return periods (>1000 years, based on current conditions) are likely to occur more frequently in the future, highlighting the possibility of flood intensification. Regardless of the length of return period, areas with infrequent flooding but large inundation depth and those with more frequent flooding but small inundation depth were classified as high risk. The proposed method provides a baseline framework for future flood risk assessments and the results highlight the importance of incorporating (currently) rare heavy rainfall events in future flood management evaluation and planning.