天山乌鲁木齐河源高山区的降水特征

Characteristics of Precipitation in the Source Area of the Urumqi River Basin

The relative variability of the annual precipitation ranges around 10%. Summer precipitation, with great precipitation days and hours, is much more than other seasons. Trace amount of precipitation frequently occures in summer. The dinual pattern of summer precipitation is characterized by the daytime concentrations. Measurements show an increase tendency of summer precipitation with the elevation along the river valley up to 4 030 m a. s. l. in the accumulation area of the glaciers. This is caused by systematic weather processes. On an average, annual precipitation in the source area of the river basin does not change significantly during 1960s and 1980s. However, the variation range of the annual precipitation series tends to increase apparently.