Extreme anticyclonic anomaly linked to catastrophic rainfall in Henan and marine heatwave

A study published in Advances in Atmospheric Sciences has unveiled the unprecedented nature of an anticyclonic anomaly over Northeast Asia in July 2021, which played a key role in both the extreme precipitation in Henan Province, China and a severe marine heat wave in the Japan Sea. This phenomenon resulted in significant ecological and economic impacts, including the deaths of 380 people in Zhengzhou and record-breaking losses to Japan’s coastal fisheries.

In July 2021, Northeast Asia experienced an anticyclonic anomaly of unmatched intensity and duration, leading to catastrophic extreme weather conditions, according to research published this month in Advances in Atmospheric Sciences.

This anomaly was central to the severe precipitation in Henan Province, central China, causing widespread flooding affecting 150 counties and 147.86 million people, with direct economic losses reaching 1,200.6 billion yuan. Zhengzhou, the capital city of Henan, saw a tragic loss of 380 lives on July 20.

The rainfall it produced in Henan was described at the time as the worst in 1 000 years.

The anomaly also induced the strongest marine heat wave in the western North Pacific in four decades, resulting in a widespread harmful algae outbreak along Japan’s coastlines, devastating marine ecosystems, and causing unprecedented losses to the fisheries sector.

Prof. Lu Riyu, the study’s corresponding author from the Institute of Atmospheric Physics of the Chinese Academy of Sciences, highlighted the anomaly’s persistence over 10 consecutive days, from July 13 to July 22, 2021, emphasizing its role in these extreme climate events.

Further analysis revealed the anticyclone led to exceptionally high sea surface temperatures in the Sea of Japan/East Sea for 30 consecutive days from July 13 to August 11, 2021, suggesting the anomaly’s impact lasted well beyond its presence in the atmosphere.

The study explored possible reasons for this long-lasting anomalous anticyclone, and it is suggested to be a byproduct of a teleconnection pattern over extratropical Eurasia during the first half of its life cycle, and of the Pacific–Japan teleconnection pattern during the latter half.

This comprehensive study shows the critical importance of understanding such extreme anticyclonic events, highlighting their capacity to trigger multiple climate catastrophes over different regions and emphasizing the need for improved monitoring and prediction methods to mitigate future extreme weather impacts.

References:

¹ Unprecedented anticyclonic anomaly in northeast Asia triggers extreme weather events and prolonged marine heat wave – Chinese Academy of Sciences – February 23, 2024

² The Unprecedented Extreme Anticyclonic Anomaly over Northeast Asia in July 2021 and Its Climatic Impacts – Xingyan Zhou & Riyu Lu – Advances in Atmospheric Sciences – February 9, 2024 – https://doi.org/10.1007/s00376-023-3026-5

Featured image credit: Rita Bai Yunyi