Why is the rainy season in South China so long this year?

Zhao Zhenguo, a researcher at the National Climate Center, believes that precipitation in some areas of southern China has exceeded the average level of the year, causing floods. "Most parts of southern China generally enter the rainy season and flood season from April to June, and this year's precipitation has not increased significantly. The drought in the north should be more of a cause for concern than the precipitation in the south.

The drought in the north has lasted for many years, and the drought in the southern part of Northeast China and most parts of North China has been occurring once in decades, and some counties have even broken the drought record of a century. The floods in the south are not very serious, while the drought situation in the north is already very serious. He said that this year's heavy precipitation in the south and drought in the north are the result of a combination of factors

Drought is becoming more and more severe due to the continuous decrease in precipitation and insufficient surface runoff for many years. This year's high temperatures and windy spring fueled evaporation on the ground. The anomaly of the East Asian atmospheric circulation also affects the precipitation in China. Before May this year, cold air from the north of China frequently moved south, but there was not enough water vapor in the atmosphere. Since May, a warm high pressure has occurred in East Asia, weakening the strength of cold air from the north to the south.

In this way, there are fewer opportunities for cold air to interact with water vapor, and if the precipitation conditions are not available, there will be less natural precipitation. The temperature of the Pacific Ocean east of the equator is still in a cold state, which also makes the spring drought and lack of rain in China. Although La Niña ended last spring, the water temperature in this area is still not high; There is a cyclical variation in precipitation. The 70s of the 20th century was the turning point of periodic precipitation in China, and there was more precipitation in the north and less precipitation in the south.

After the 70s, it was reversed, with a gradual decrease in precipitation in the north and a gradual increase in precipitation in the south. A change cycle of precipitation is about 30 years, and drought and lack of rain will still occur in the north in the next few years. Zhang Yan, a professor at the China Meteorological Administration, believes that the main reason for the current heavy precipitation in the south is that "the rainfall belt stays in the south for a long time and does not come to the north."

After research, she also found that in the past half century, in the overall environment of global warming, the variability of precipitation and drought in China has increased, "which is prone to long-term drought and precipitation, and the impact of continuous drought in some areas on local industry and agriculture is also increasing, and even affects the south-to-north water diversion." ”

Affected by El Niño, there was more precipitation in the south this year.

It mainly brings flooding.

The recent rain has really affected everyone's mood. Because of the rain, there are geological disasters in some parts of the south, but you don't have to worry too much. The rainy season will soon pass. After this rainy season, you will usher in summer.

July 9, 2010 - July 9, 2010.

From the Jianghuai River Basin in China to the early summer (June to July) in southern Japan, there is a period of continuous rainy weather, heavy precipitation, and frequent precipitation.

Because the plum is yellow and ripe, hence the name. Due to the high temperature, high humidity and rainy water at this time, the utensils are easy to be damp and moldy, so it is called mildew rain.

Generally, plum blossoms bloom from early to mid-June, from early July to mid-July, and summer begins.

1.Normal rainy season.

The southern region opens around June 15 and ends around July 15. The rainy season lasts for about 20-30 days, and the rainfall is maintained at about 200-400mm, so the rainy season is normal.

2.Early rainy season.

If there is a rainy season at the end of May and early June, it means that the rainy season is early.

3.Chi Meiyu.

The rainy season around June 15 is called the red plum rain.

4. Special rainy season.

The rainfall from May to July is an unusually high 900 mm, and it is called the long rainy season.

5.Short plum and empty plum.

Some rainy seasons are short, with only ten days, or no rainy season at all.

6.Pour yellow plums.

There was no sign of the rainy season at the beginning of the nuclear process, and the summer was hot, but there were sudden thunderstorms.

In June and July, 500mb in the northern hemisphere, the western Pacific subtropical high ridge position: 23-24n, 24-north of Zhejiang, and has been stable for more than five days.

Occurs after the end of continuous rainfall:

More than seven days in southern Zhejiang and more than five days in northern Zhejiang, basically no rain (excluding precipitation caused by the southern tropical system and local thunderstorms).

The average daily temperature is above 25 degrees. c or above. The daily average temperature and pressure time curves of a single station increased simultaneously. If the subtropical ridge moves northwards to 25 degrees. n.

If it is stable for two hours, and there is still continuous rainy weather greater than or equal to millimeters during this period, a day with daily rainfall greater than or equal to millimeters is selected.

After the rainy season, 120-130. The subtropical ridge of high pressure moved northwards to 26 degrees. or north of n, the average daily temperature, the highest temperature, and no rain for more than 6 consecutive days. The average annual plum blossom date is July 9.

When the ridge of the subtropical high jumps north to north of 26. n and stable for more than 3 days, the last provincial precipitation process of more than 2 days in Hankou, which was controlled by the peripheral line of the subtropical high (588 dagpm), will end and be designated as plum blossom.

Zhou Bing, chief of climate services at the National Climate Center, said that the 2018 pre-flood season in South China first started in Guangxi on April 20, 14 days later than the normal April 6, and the first flood season in Guangxi in the past 60 years was only 5 years and months to May, and the average precipitation in South China was less than that of the same period in the normal year, resulting in different degrees of meteorological drought in Xianglu. At the beginning of June, Typhoon No. 4 "Ewini" made landfall in Guangdong three times, bringing abundant dragon boat water and alleviating the drought to a certain extent.

China has a typical monsoon climate, which is cold and dry in winter under the influence of dry and cold air currents from the mainland; The summer dry season is affected by the warm and humid air currents from the ocean, and it is hot and rainy. The activity of the summer monsoon in the South China Sea is the "driving force" behind the activities of the rain belt in China, so its early failure will have an important impact on China's climate.

So the feeling of netizens is right, the rainfall in South China this year is indeed not as much as in the past, the main reason is that the western Pacific subtropical high pressure system is extremely strong, the ridge position is northerly for a long time, and South China has been in fine weather controlled by the high pressure system for a long time. **: China Meteorological Network.