What is the criterion for judging rainstorm?

There are three criteria for judging rainstorm, which generally refer to the precipitation with hourly rainfall greater than16mm, or continuous rainfall greater than 30mm within12h, or continuous rainfall greater than 50mm within 24 hours. According to China's meteorological regulations, rain with a precipitation of more than 50 mm in 24 hours is called "rainstorm". According to its precipitation intensity, it can be divided into three grades: "rainstorm", "heavy rainstorm" and "extremely heavy rainstorm". "Rainstorm" refers to the precipitation with a 24-hour precipitation of 50-99.9 mm; "rainstorm" refers to the precipitation below 100 ~ 200mm; "Extraordinary rainstorm" means that the precipitation exceeds 200mm.

Due to different regions and different topographical features, the storm and flood standards in each region are also different. Rainstorm is a kind of disastrous weather, which often causes floods and serious soil erosion, leading to major economic losses, such as engineering accidents, dike burst and crop flooding. Especially for some low-lying and relatively closed areas, heavy rain will cause greater disasters to agriculture.

The world's largest rainstorm occurred in Reunion Island in the South Indian Ocean, when the 24-hour precipitation reached 1870 mm, and the largest rainstorm in China occurred in Xinliao, Taiwan Province Province, where the 24-hour precipitation was 1672 mm, all caused by tropical cyclone activities. China is one of the countries with the most rainstorms in the world, and almost all provinces (cities, districts) have rainstorms. Mainly concentrated in the second half of the year. The regional distribution of rainstorm days is obviously more in the south and less in the north; There are many coastal areas and few inland areas; There are many windward slopes and few leeward slopes. The annual average number of rainstorm days in mountainous areas of Taiwan Province Province is more than 16 days, and Dongxing, Yangjiang, Shanwei and some coastal areas of South China are more than 10 days. On the contrary, the annual average number of rainstorm days in northwest China is less than 1 day.

For example, the rainfall of 50 mm is evenly distributed within 24 hours, giving people the impression that it is Mao Mao rain. If the precipitation of 9 mm is completed within one minute, it will give people a feeling that the sky is falling, which is not described by downpour. Everything is relative and has its specific background. In southern China, the standard of rainstorm is basically 80mm/24h, but this definition needs to be further improved.