What natural disasters have occurred in Suzhou for decades?

① The 33 counties belonging to the Yangtze River valley in Jiangsu are Taicang, Kunshan, Changshu, Wuxian, Wujiang, Shazhou, Jiangyin, Wuxi, Yixing, Wujin, Jintan, Danyang, Dantu, Yangzhong, Jurong, Liyang, Lishui, Jiangning, Gaochun, Jiangpu, Liuhe, Yizheng, Hanjiang, Jiangdu, Taixing and Lishui. The 3 1 counties in Huaihe River Basin are Fengxian, Peixian, Tongshan, Pixian, Juning, Xinyi, Suqian, Shuyang, Donghai, Ganyu, Guanyun, Guannan, Xiangshui, Binhai, Lianshui, Funing, Yancheng, Sheyang, Dafeng, Dongtai, Jianhu and Sihong. In recent years, some counties have been changed to cities and districts, and the names of counties may also change. In order to keep consistent with the place names of county records, they are still arranged according to the original names.

As can be seen from the above table, during the 350 years of 1644- 1993, the Yangtze River and Huaihe River basins in Jiangsu Province suffered severe floods and droughts 1 15 times, including 53 times in the Yangtze River basin and 62 times in the Huaihe River basin, and the Huaihe River basin was more serious than the Yangtze River basin. In other words, the Yangtze River basin occurs once every seven years. In addition, from the perspective of the whole province, in these 350 years, disasters occurred in 92 years, and only 2 1 year disasters occurred in two river basins at the same time, and most of the other years were only disasters in one area. This shows that although the climate in the north and south of Jiangsu has certain homogeneity, the difference is even greater. Of course, if two river basins and one area are affected at the same time, a serious flood and drought disaster may occur in Jiangsu every 3-4 years, which is a very noteworthy year.

From the above table, we can also know that in these 350 years, there have been 29 floods and 24 droughts in the Yangtze River basin, with more floods than droughts. The Huaihe River Basin is flooded by 5 1 and arid by1. Although there are more floods than droughts, floods are several times as many as droughts, far exceeding the ratio of floods to droughts in the Yangtze River basin. In the past, some people thought that the frequent floods in the Huaihe River basin were affected by the Yellow River seizing the Huaihe River. However, after 1855, the Yellow River returned to the Shandong Sea, and the number of floods and droughts in the Huaihe River Basin in Jiangsu Province was still 2 1∶7, which was three times that of the severe drought. Although it is lower than before 1855, it is still much higher than the Yangtze River basin. The reason is mainly related to the great change of precipitation and poor water receiving conditions in Huaihe River Basin. It can be seen that although the annual precipitation in Huaihe River basin is not as large as that in Yangtze River basin, the possibility of flood is greater than that in Yangtze River basin. Waterproofing is more important than drought prevention in this area. If we compare the disasters in the two river basins at the same time, we can find that in 2 1 * * the same disaster years, only1and 97 1 are drought in the south and water in the north, and the disasters in the north and south are the same in other years, either flood or drought. This is because if both the north and the south suffer disasters, they are often controlled by a large-scale weather system under the same climatic conditions, and the resulting disasters also have the same nature. For example, 1954, the Yangtze River and Huaihe River flooded together because "the sea of Okhotsk maintained a continuous high pressure in July, which made the air over the Yangtze River and Huaihe River become a long-term intersection of cold and warm air, resulting in a continuous and lasting rainfall process". ① If there are disasters in the north and south, but the nature of the disasters is different, not only the time may be different, but also the nature of the weather system is often different. For example, 197 1 The flood in the north was caused by continuous rainfall in early June, while the drought in the south was caused by continuous high temperature and little rainfall after late June. Obviously, the causes of the two are not the same weather system.