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Southern China sees abnormally heavier rainfall season in 2020

27-07-2020Source:China Meteorological News Press

Since June, 2020, South of the Yangtze River Region, middle and lower reaches of the Yangtze River Region and Jianghuai Region have entered the plum rain season in succession. Weather and climate conditions are complex and extreme events crop up frequently. Southern China is exposed to large scale continuous heavy rain, with big cumulative rainfall, extreme intensity, and heavy hazards.

According to Academician Ding Yihui from Chinese Academy of Engineering and researcher from Beijing Climate Center (BCC), global warming is a key contributor to frequent extreme weather and climate events. In the meanwhile, subtropical high in 2020 held steady, making water vapor transportation from Tropical Ocean abnormally stronger. The cold air from northern China continues to move southward, with the cold air and warm air converging over the Yangtze River Basin, bringing forth continuous rainfall.

Early entry into the plum rain season, more days of rainstorm, and longer duration

Spatial distribution map of precipitation of China since June, 2020

Overlapped areas of rain with heavy cumulative rainfall

Precipitation in Anhui, Hubei, and Chongqing is the heaviest compared with the same period in normal years.

Since June, southern China is exposed to rain of extreme intensity. Daily precipitation in 108 stations has reached the monitoring threshold of extreme events.

Extreme precipitation event distribution of China from June 1 to July 21, 2020

Since June, precipitation in the Yangtze River Basin has registered 486.8 mm, 54% heavier than that of the same period in normal year. It is the heaviest of the same period of normal years since the 1961.

Precipitation in Taihu Lake basin registered 666.9 mm, 1.1 times heavier than that of the same period in normal year. It ranked the second compared with that of the same period of normal years. 

 

 

 

Historical change map of average precipitation change in the Yangtze River Basin from June 1 to July 21 (1961-2020)

Why the plum rain is so much in this year?

Human activity

Scientific research shows that rise of major greenhouse gases concentration caused by human activity is a main contributor to global warming, thus further giving rise to the changes of frequency, intensity, spatial scope and duration of global extreme weather and climate events.

Global warming will also alter large scale atmospheric circulation conditions, and affect the emergence rules of extreme weather and climate events in diverse regions via the changes of the interaction between the sea and the air, and the interaction between the land and the air. Some extreme weather and climate events are on the rise and take on the change from the perspective of long duration.

In the past six decade, extreme weather and climate events in China like high temperature and heavy rain are characterized by stronger intensity, more frequency, and longer duration.

Early entry into the plum rain season and stronger meiyu front

Plum rain is a major weather and climate system during the flood season of China.

According to Ding Yihui, early entry into the plum rain season and stronger meiyu front are the direct cause of abnormally heavier rain in the middle and lower of the Yangtze River during the flood season.

A weak El Nino Event started from the autumn of 2019. North Indian Ocean witnessed abnormally warmer sea temperature, resulting in stronger subtropical high. And the water vapor transportation introduced by the subtropical high to the middle and lower reaches of the Yangtze River was remarkably stronger. The cold air and warm air converged in the middle and lower of the Yangtze River, leading to stronger meiyu front and heavier rainfall in the region.

The cold air and warm air converged in the middle and lower of the Yangtze River

In the meanwhile, due to stronger subtropical high in Northwest Pacific, atmospheric convection movement over Northwest Pacific is inhibited, which is not favorable for typhoons to form. (July. 27)

Editor: Liu Shuqiao