Assessment of climate change impacts on river flooding due to Typhoon Hagibis in 2019 using nonglobal warming experiments

In this study, a series of numerical analyses of meteorology, runoff, river flow, and inundation were performed to quantitatively evaluate the effects of historical warming on precipitation, discharge, water level, and flood inundation. This study was on the flood inundation of the Chikuma River Basin in Japan caused by Typhoon Hagibis in 2019. The historical warming impact on Typhoon Hagibis was analyzed by comparing nonglobal warming experiments (NonWs) and control experiments (CTLs) to reproduce the current situation. Calculated results showed that the ratios of the index of CTLs to that of NonWs (mean CTL to mean NonW) as indicators of the impact of historical warming were 1.08, 1.22, and 1.08–3.08 for total precipitation, peak river discharge, and peak water level (from pre-flood level and high-water level), respectively, and 48.1 and 595 for overflow depth and inundation volume for the Chikuma River, respectively. Results of the hydrologic-sensitivity analysis indicated that the influence of historical warming during the last 40-year period was already evident on overflow and flooding, whose sensitivities were higher than those of discharge and water level.