What are the characteristics of Huaihe River?

Judging from the water pattern, the average annual precipitation in Huaihe River Basin is about 920mm, and its distribution generally decreases from south to north, with mountains more than plains and coastal more than inland. There are three high precipitation areas in the basin: one is Funiu Mountain area, with an average annual precipitation of more than 1000mm; Second, Dabie Mountain area, 1400mm or more; ; The third is the downstream offshore area, which is above 1000 mm, and the precipitation in the northern part of the basin is the least, which is below 700 mm. The precipitation changes greatly during the year, and the maximum annual rainfall is 3-4 times of the minimum annual rainfall. The annual distribution of precipitation is also extremely uneven, and the precipitation in flood season (June-September) accounts for 50%-80% of the annual precipitation.

During the flood season from May to August in Huaihe River Basin, the rainfall in three months is usually 500-600 mm, especially in June-July, which is a unique rainy season in Jianghuai area, and the rainfall can last for one or two months. Wide range, covering the whole basin; Rainy years alternate with poor harvest years, and the average difference in precipitation is four or five times. Studying the history of disasters in Huaihe River, it is found that there have been 13 1 times of basin floods in recent 530 years. Among them, floods are more than once every three years on average. Historically, the Yellow River "seized the Huaihe River and entered the sea", and the sediment in the lower reaches of the Yellow River aggravated the geographical characteristics of poor drainage of the Huaihe River, making waterlogging an important form of flood in the Huaihe River.

Typhoon (including typhoon inverted trough), vortex shear, north-south shear and cold shear line are the weather systems that produce heavy rain in Huaihe River basin, and the first two are mostly. Vortex shear type is the main type in the early rainy season, and typhoon is involved in the later rainy season. The typhoon track covers the whole basin.

The trend of rainstorm is generally consistent with the movement of weather system, and the center movement of typhoon rainstorm is related to the typhoon path. Cold peak rainstorm usually moves from northwest to southeast, and vortex rainstorm usually moves from southwest to northeast. With the intersection of north-south airflow, the shear line or front swings north-south, southeast and northwest, and the rainstorm center moves with it. For example, in July of 1954, several heavy rains were caused by the vortex shear line. The rainstorm first appeared in the mountainous area of Huainan, then advanced to the Hongru River and Sha Ying River basin in the northwest, then moved eastward to Huaibei area, and finally disappeared in northern Jiangsu. A precipitation process affected the whole Huaihe River basin. Because the moving direction of rainstorm is close to the direction of river, the Huaihe River basin is prone to flood disaster.