HAPpy Hour Seminar - Response Experiments of Heavy Rainfall Events to Global Warming and the Related Quantitative Climate Change Risk Estimation of Floods

May. 26, 2023

3:00 – 4:00 pm MDT

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Yasutaka Wakazuki

Ibaraki University, Japan
Response Experiments of Heavy Rainfall Events to Global Warming and the Related Quantitative Climate Change Risk Estimation of Floods

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Meeting ID: 971 0525 3171
Passcode: HAPpyhour1

Future Projections of the line-shaped convective system using regional climate model simulation and pseudo global warming experiment By Prof. Naka (Kyoto University)

In recent years, many hydrological disasters related to heavy rainfall have been caused by the Baiu frontal precipitation systems and typhoons. Many studies point out that heavy rainfall events have increased in recent years, and heavy rains and floods are predicted to intensify and become more frequent in the future climate. However, many unknowns exist, such as how individual heavy rainfall events will be modified due to global warming. This study investigated how mesoscale heavy rainfall phenomena change by applying high-resolution simulations with a non-hydrostatic cloud resolving atmospheric model and the pseudo-global-warming method. Three different types of events were selected for the investigation: Heavy rainfall at Northern Kyushu in July 2017, Western Japan in July 2018, and Typhoon Hagibis in 2019. In addition, we applied the water budget analyses to understand climate changes in characteristics of precipitation associated with the terrain effects. Moreover, climate changes in flood risks were quantitatively estimated using a river model.
To estimate the effects of global warming, climatological increments of air temperature and water vapor, calculated from the d4PDF data set, were applied in the pseudo-global-warming experiments. Two climatological increments in global mean temperatures since the Industrial Revolution were assumed to be 2 and 4 °C, corresponding to temperature increases around 2040 and 2100 based on the RCP8.5 scenario. In addition to the regular future climate experiments (stabilization increment experiments), neutral increment experiments were performed, in which the air temperature increase is uniform for all vertical levels.
The atmospheric model simulations reproduced precipitations well. In the future climate experiments, precipitation increased in all 2- and 4-°C stabilized and neutral experiments. In particular, a significant increase in precipitation was observed in the 4-°C neutral experiment. The atmospheric water budget analyses derived that water vapor increase affected precipitation enhancement for all cases. In addition, dynamic effects related to the intensification of convictions resulted in increased precipitation that exceeded the CC effect. In the case of Typhoon Hagibis, the convergent-enhancement impact on the mountain slopes of the Kanto Plain significantly contributed to the enhancement of precipitation. In the case of the Baiu frontal rainband on the Northern Kyushu, the enhancement of line-shaped rainbands largely contributed to the enhancement of precipitation. The impact of the enhancement of precipitation is significantly related to the climate change of river flooding risk. For flood risk assessment in Typhoon Hagibis, future climate experiments were conducted after confirming the better reproducibility of the RRI model. In particular, the maximum depth of water and the maximum flooded area in the Naka River basin in the 4-°C experiment were significantly increased because precipitation in the mountainous regions was predicted to increase considerably in the Naka River basin.


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