The city's average rainfall amounted to 331 millimeters, and the rainfall in 83 hours was 60 percent of the perennial annual average.

Beijing's average multi-year precipitation (covering rainfall, snow, hail, etc.) is 626 millimeters. However, because of the influence of the terrain, it can be divided into three zones: the pre-mountainous areas in the west and southwest, where the average annual precipitation reaches about 700 millimeters; Miyun, Huairou, Pinggu and the plains in the north, which can reach up to 600 millimeters; and the mountainous areas in the northwest, where the precipitation is lower, at about 400 millimeters only.

Precipitation in Beijing is also affected by the monsoon, and is extremely uneven in seasonal distribution, i.e., it is mostly concentrated in the summer, accounting for more than 70 percent of the annual precipitation; winter and spring are the least, accounting for only 11 percent. The inter-annual variation of precipitation is also significant. According to more than 100 years of meteorological data analysis, as much as 1406 millimeters in the year of abundance of water (1959), only 242 millimeters in the year of dry water (1869), the difference between the two nearly six times. Because the seasonal distribution of precipitation is extremely uneven, from time to time to make Beijing's rivers rise and fall, the flow is extremely unstable, forming a disaster.

Division of rainfall grades:

Rainfall grades are light rain, with a total of 1-10mm in a day, and the ground is wet but not muddy;

Rainfall grades are medium rain, with a total of 10-25mm in a day, and you can hear the sound of pattering on the roof, and there are pools of water in depressions of the ground;

Rainfall grades are heavy rain, with a total of 20-50mm in a day, and it rains like a downpour;

Rainfall grades are heavy rain, with a total of 20-50mm in a day, and it rains like a downpour. 50mm, rain as pouring down, landing splash, water on the ground;

Rainfall level of heavy rainfall, rainfall totaling 50-100mm in a day, gusty winds, accompanied by thunder and lightning, there is at this point in time the amount of rainfall has been enough to trigger flash floods.

Rainfall level for heavy rainfall, rainfall totaling 100-200mm in a day, this rain out of the black clouds, accompanied by gusty winds and thunderstorms, easy to cause flooding.

The rainfall level is extremely heavy rainfall, the total rainfall of more than 200mm in one day, it is not easy to meet, if it occurs more into flooding.