Scientists Explore Synergistic Effect of Weather Systems on a Central China Flood


In July 2021, Henan Province in central China experienced an extraordinary event - a prolonged heavy rainfall period marked by record-breaking hourly rain rates and substantial precipitation accumulation. The event took place in an anomalous synoptic circulation pattern: the coexistence of a northwestward-shifting western Pacific subtropical high (WPSH) and Typhoon In-Fa (2021) over the East China Sea. However, few studies have focused on the synergistic effect of the WPSH and Typhoon In-Fa on this particular heavy rainfall in Henan. 

Pedestrians and vehicles trudged on the flooded street during rainfall in Zhengzhou Henan on 21 July 2021. (Image by LIN Lyuhua)

A team of researchers led by Professor CHEN Guanghua at the Key Laboratory of Cloud-Precipitation Physics and Severe Storms of the Institute of Atmospheric Physics at the Chinese Academy of Sciences, the researchers reveal the intricate physical mechanism responsible for this remarkable weather occurrence, by conducting a series of numerical simulations.
Published in Journal of Geophysical Research: Atmosphere, the results confirm that this heavy rainfall event in the summer of 2021 unfolded under the highly favorable WPSH and Typhoon In-Fa circulations and their cooperation. Notably, the study highlights the greater contribution of Typhoon In-Fa in amplifying the rainfall compared to the WPSH.
Additionally, the research identifies the critical role played by the expansive and strong nature of the WPSH and Typhoon In-Fa in enhancing the northward and westward moisture transports, respectively. Conversely, weakening of these systems leads to a decrease in moisture transport. Moreover, the distribution of equivalent potential temperature and divergence were found to be closely linked to the region of heavy rainfall.
Professor CHEN, the corresponding author of the study, emphasizes the importance of further exploration in this field. He states, "This study serves as a preliminary endeavor to comprehend the synergistic effects of weather systems on heavy rainfall. Ongoing research aims to delve into the interactions among multi-scale systems." 
As climate change continues to escalate, the frequency and intensity of extreme weather events are anticipated to rise. Understanding the factors driving these events is of paramount importance in enhancing preparedness and mitigating their impact.
Rao, C., Chen, G., & Ran, L. (2023). Effects of Typhoon In-Fa (2021) and the western Pacific subtropical high on an extreme heavy rainfall event in central China. Journal of Geophysical Research: Atmospheres, 128, e2022JD037924.
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