Weather system types in Tumen River
Temperate continental monsoon climate. The basin has a temperate continental monsoon climate, with windy and dry springs, warm and rainy summers, cool and foggy autumns, and long and cold winters. The intra-annual and inter-annual distribution characteristics of precipitation are as follows.
1. Mainly rainwater, with annual precipitation of 500~700mm.
2. Precipitation is extremely unevenly distributed throughout the year. In winter, controlled by dry and cold polar continental air masses, precipitation only accounts for 1% to 5% of the annual precipitation. The precipitation in January is less than 1% of the whole year, and most of it is drifting snow. Cyclone activity increases in spring, and precipitation increases accordingly. The precipitation accounts for 10% to 20% of the whole year, of which the precipitation in April accounts for 3% to 6% of the whole year. Affected by the southeast monsoon in summer, precipitation accounts for 50% to 70% of the annual precipitation, and the maximum precipitation occurs in August.
3. Precipitation is significantly affected by topography in the region. In the upper reaches of the basin and the windward slope of the Hunchun River Basin, the annual precipitation is 600-700mm, which is a high-precipitation area. The precipitation in the Yanji Basin and Helong Basin on the leeward slope is about 500mm, which is a low-value area. In the mountainous areas of the northwest, precipitation has increased due to terrain uplift, generally ranging from 500 to 600mm. In general, the basin has relatively abundant precipitation and abundant water sources.
4. The inter-annual variation in precipitation is small. The rainfall in the basin is 1140mm in the richest year and 260.3mm in the lowest year. The ratio of the maximum annual precipitation to the minimum annual precipitation is 4.4. This value is similar to the vast rainy area south of the Huaihe River in the Qinling Mountains, but smaller than that in North China and the western part of Northeast China.