Extreme river flood induced by the 2019 Typhoon Hagibis at Shinano River basin under climate change conditions

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Study region Shinao river basin, Japan Study focus This study focuses on extreme river flood at the Shinano River, in Japan, caused by Typhoon Hagibis (2019) under historical and warmer climate conditions by using meteo-hydrological and hydrodynamic models. The simulated rainfall, river discharge and inundation area considering levee breach were in good agreement with the observations from meteo-hydrological stations, post-field survey and satellite imagery. Hydrological characteristics within the steep basin under historical and climate change conditions were evaluated based on modeling results. New hydrological insights for the region Pseudo global warming (PGW) experiments under SSP5–8.5 scenario (Shared Socio-economic Pathways with radiative forcing level of 8.5 Wm −2 ) for the 2050 s, where nearly 99.7 % of warming is human-induced, showed that area-averaged rainfall increased by 15 %, leading to an increase in the river discharge by 42 % at the Tategahana station. The lag time between maximum area-averaged hourly rainfall and the peak river discharge could be slightly shorter under PGW conditions. Sensitivity analysis showed a significant increase in the inundation area from 8.22 ∼13.33 km 2 under historical to 10.08 ∼ 14.11 km 2 under PGW conditions, corresponding to 7.04 ∼ 22.62 % increase due to prolonged high flows in the future hydrograph. These findings provide valuable insights for regional stakeholders for disaster risk management and planning associated with intense typhoon-driven severe floods under anthropogenic climate change.

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