The precipitation in Beijing has several characteristics: First, there is great interannual change. For example, in 1959, the maximum annual precipitation reached 1406 mm, while in 1969, the minimum annual precipitation was only 242 mm, and rainy years were 5.8 times that of dry years, and rainy and dry years sometimes occurred. Second, the seasonal distribution is uneven, and the precipitation intensity in summer is high. June-August in summer is the rainy season, and the precipitation points account for more than 70-75% of the whole year; There is little rain and snow in winter, and the precipitation points account for 20% of the whole year; Less in spring, accounting for 8-10% of the whole year; Autumn 13- 16%.