How to prevent plum rain?

Meiyu is a weather phenomenon that occurs every year, and it is beyond human intervention.

However, the flood disaster caused by this can not be ignored.

1, the government and relevant departments should do a good job in rainstorm prevention according to their duties;

2. The traffic management department takes traffic control measures in heavy rainfall sections according to the road conditions, and implements traffic guidance in waterlogged sections;

3. Cut off the dangerous outdoor power supply in low-lying areas, suspend outdoor work in open-air places, and transfer people in dangerous areas and residents of dangerous houses to safe places for shelter from the rain;

4, check the city, farmland, fish pond drainage system, take the necessary drainage measures.

In early summer, there are often long rainy days in the Jianghuai basin. At this time, the utensils are easy to be moldy, so it is also called "moldy rain" or "mildew" for short; It is also called "Plum Rain" or "Huang Meiyu" because plums in the south of the Yangtze River are yellow and ripe. It is recorded in China's historical records. For example, The Book of Beginners quoted the compilation of Emperor Liang Yuan in the Southern Dynasties, "Plum blossoms have plum rains when they are ripe". Liu Zongyuan's Plum Rain in the Tang Dynasty: "Shi Mei welcomes the rain, and it is worth the late spring." Wait a minute. It is recorded in China's almanac that there is mildew rain all day: it is called "mildew" at the beginning and "mildew" all day long. The first day after the awn is planted, it will be moldy, but it will not be moldy on the first day after the light summer. Mold always enters from June 6th to 15, and mold always leaves from July 8th to 19. There is an obvious rainy season in the eastern part of China, with a long rainy period and relatively concentrated rainfall, which is caused by the displacement of the main rain belt from east to west to north, and is a unique phenomenon in the turn of atmospheric circulation in East Asia at the turn of spring and summer. After mid-June, the rain belt remained in the Jianghuai basin, which is Meiyu. The time that the rain belt stays is called "Meiyu season", the day when the rainy season begins is called "entering the plum blossom", and the day when it ends is called "emerging the plum blossom".

In addition, due to the high humidity in the air during this period, everything is easy to be damp and moldy, so people gave Meiyu an individual name, called "Moldy Rain". Xie Zaihang's Five Miscellaneous Torches in Ming Dynasty? "Tianbu No.1" describes: "Every year in March and April in the south of the Yangtze River, it rains bitterly, and everything is moldy, commonly known as Meiyu, and it is covered when it is green and yellow. From Xu Huai to the north, it is often dry in spring and summer. At the turn of June and July, it rained heavily and everything was moldy. " Li Shizhen, an outstanding medical scientist in Ming Dynasty, pointed out more clearly in Compendium of Materia Medica: "Plum rain or mildew rain, when it comes to clothes and things, will produce black mold." .

The middle and lower reaches of the Yangtze River in China are usually rainy from mid-June to early July every year. In the past few days, the sky has been gloomy and the precipitation has been constant, sometimes big and sometimes small. Therefore, there is a popular proverb in southern China: "Rain hits plum blossoms, and there is no sun for forty-five days". Continuous rain, high temperature and high humidity are the main characteristics of plum rain.

Very different from the climate in the same latitude area, Meiyu refers to the weather and climate phenomenon that occurs in a certain area and a certain season. It is found that Eurasia is between 20 N and 40 N, which is alternately controlled by subtropical high and westerly belt. The west coast of the mainland is controlled by the downdraft on the east side of the subtropical south pressure in summer, with sunny weather, partly cloudy and dry climate; In winter, under the influence of westerlies, warm and humid air is brought from the Atlantic Ocean, resulting in more precipitation and a mild and rainy climate. That is, the subtropical Mediterranean climate is dry in summer and humid in winter.

The east coast of the mainland is controlled by the west side of subtropical high in summer, and the downward flow is dry, but it absorbs a lot of water vapor from the warm and humid sea surface, bringing abundant precipitation and producing a subtropical humid climate. Due to the strong contrast between land and sea, a unique monsoon climate has formed here, which is characterized by rainy summer and dry winter, with rainfall concentrated in summer, which is just the opposite of the Mediterranean climate.

If compared with the east coast of Britain at the same latitude, it is also very different. There will be no rainy weather for a long time before and after the summer monsoon in the mid-latitude zone of the east coast of the United States, and people do not feel the feeling of sultry weather for a long time, so it is difficult to appear moldy. It can be seen that the precipitation season at the same latitude varies greatly. So there are only Huangmei in the middle and lower reaches of the Yangtze River in China, starting from the area east of Yichang and 29-33 degrees north latitude, as well as the southeast of Japan and the southernmost tip of the Korean Peninsula. In other words, Meiyu is a unique weather and climate phenomenon in East Asia and the middle and lower reaches of the Yangtze River in China.

The atmospheric circulation conditions that form the Meiyu front rainstorm generally include:

① There are blocking high pressure or stable high pressure ridges in the middle troposphere at high latitudes in Asia, and the atmospheric circulation is relatively stable and rarely changes;

② The westerly circulation in mid-latitude area is flat, and frequent short-wave activities provide cold air conditions for Jianghuai area;

③ The western Pacific subtropical high has an obvious process of extending westward and jumping northward. The ridge line of the 500 HPA subtropical high is stable between 20 and 25 degrees north latitude, and the warm and humid air flow is transported from the edge of the subtropical high to the Jianghuai basin. Under this circulation condition, Meiyu front lingers in the Jianghuai basin, often accompanied by southwest vortex and shear line, and the mesoscale system on Meiyu front is active. It not only maintains the continuous precipitation during the Meiyu period, but also provides abundant water for the rainstorm.

Meiyu front rainstorm is a special weather in a specific area formed by the interaction of circulation systems of different scales. The variability of atmospheric circulation leads to the late start and short duration of meiyu period every year. In some years, the Meiyu front is particularly active, with frequent rainstorms, leading to flooding. In some years, the meiyu front is not obvious, and there are "empty plums", which leads to dry weather. In some years, the Meiyu belt will move northward and then return to the Jianghuai basin to maintain relative stability, which is customarily called "inverted Huangmei". After the meiyu in Jianghuai basin ended, the rain belt moved to North China, and the Jianghuai basin entered high temperature and little rain.