4:21 PM - 4:46 PM
[L02-03] Intensification of Heavy Rainfall Disasters due to Global Warming: Flood Risk Assessment for All Rivers Across Japan
★Invited Papers
Keywords:Flood disasters, Climate change, Hydrologic model, Ensemble predictions
The frequency of heavy rainfall in Japan has increased significantly, with particularly intense rainfall occurring approximately twice as often as in 1980. In the future, global warming is expected to make extreme flood events more frequent and severe. Therefore, scientifically predicting flood impacts is crucial for developing effective adaptation measures. Global climate models (GCMs) are commonly used to assess the effects of global warming. Meanwhile, regional climate models (RCMs) are advancing as a means of physically downscaling GCM projections to analyze local heavy precipitation. To better understand extreme weather events, ensemble prediction methods are also progressing. For example, the d4PDF-5kmDDS dataset, developed mainly by the Meteorological Research Institute, Japan, includes simulations of climate conditions under 2°C and 4°C global warming scenarios. This dataset provides weather patterns corresponding to 720 years for each scenario, covering Japan at a high spatial resolution of 5 km.
Simultaneously, hydrological modeling has advanced, enabling more extensive and detailed flood simulations. In recent years, the field of Large-Domain Hydrology has driven the development of distributed hydrological models that cover large areas, including Japan. The authors have developed a high-resolution flood forecasting model based on the Rainfall-Runoff-Inundation (RRI) model, which integrates rainfall, runoff, and inundation processes across Japan. This model, with a spatial resolution of 150 m, includes 14,000 rivers.
Using d4PDF-5kmDDS, it is possible to estimate flood discharge corresponding to extreme rainfall events, such as those occurring once every 100 years. Furthermore, the model allows assessment of how flood discharge changes under 2°C and 4°C warming scenarios. Results indicate that flood discharge increases significantly, especially in Tohoku and Hokkaido. Under 2°C warming, the 100-year flood discharge is projected to be 1.4 times higher than in the present climate. Under 4°C warming, flood magnitude changes vary by basin size, with particularly large increases in small and medium-sized rivers. Moreover, the origins of heavy rainfall leading to flooding can be analyzed. For example, in the Tohoku region along the Sea of Japan, the increase in flood discharge is particularly pronounced due to more frequent heavy rainfall during the Baiu season.
We introduce the latest studies on these topics and will also discuss the development of an Integrated Hazard Model involving multiple researchers. This model not only incorporates the RRI model for river flooding but also includes a storm surge model for coastal flood analysis. As severe typhoons increase in frequency and intensity due to global warming, both river floods and storm surges are expected to worsen. In extreme warming scenarios, compound disasters—where river flooding and storm surges occur simultaneously—become a significant concern. This study integrates d4PDF-5kmDDS into the Integrated Hazard Model to analyze the potential for such concurrent disasters. Finally, this presentation highlights the most critical anthropogenic impacts of global warming and their consequences for severe storms in Japan.
Simultaneously, hydrological modeling has advanced, enabling more extensive and detailed flood simulations. In recent years, the field of Large-Domain Hydrology has driven the development of distributed hydrological models that cover large areas, including Japan. The authors have developed a high-resolution flood forecasting model based on the Rainfall-Runoff-Inundation (RRI) model, which integrates rainfall, runoff, and inundation processes across Japan. This model, with a spatial resolution of 150 m, includes 14,000 rivers.
Using d4PDF-5kmDDS, it is possible to estimate flood discharge corresponding to extreme rainfall events, such as those occurring once every 100 years. Furthermore, the model allows assessment of how flood discharge changes under 2°C and 4°C warming scenarios. Results indicate that flood discharge increases significantly, especially in Tohoku and Hokkaido. Under 2°C warming, the 100-year flood discharge is projected to be 1.4 times higher than in the present climate. Under 4°C warming, flood magnitude changes vary by basin size, with particularly large increases in small and medium-sized rivers. Moreover, the origins of heavy rainfall leading to flooding can be analyzed. For example, in the Tohoku region along the Sea of Japan, the increase in flood discharge is particularly pronounced due to more frequent heavy rainfall during the Baiu season.
We introduce the latest studies on these topics and will also discuss the development of an Integrated Hazard Model involving multiple researchers. This model not only incorporates the RRI model for river flooding but also includes a storm surge model for coastal flood analysis. As severe typhoons increase in frequency and intensity due to global warming, both river floods and storm surges are expected to worsen. In extreme warming scenarios, compound disasters—where river flooding and storm surges occur simultaneously—become a significant concern. This study integrates d4PDF-5kmDDS into the Integrated Hazard Model to analyze the potential for such concurrent disasters. Finally, this presentation highlights the most critical anthropogenic impacts of global warming and their consequences for severe storms in Japan.