Research On The Water Resources And Hydrological Cycle Of The Oilian Mountain

The Qilian Mountain locates in the inland of NW of china, the water coming from the glaciers of the Mountain is one of the important headstreams for several main rivers of Hexi area, so it is called the life source of the Hexi Corridor. However the complementarity of glaciers is from the rainfall of atmosphere, so it is very important to study the water resources in the air of Qilian Mountain. Utilizing the observed data of meteorological stations and the NCEP/NCAR monthly mean reanalysis gridded data, this paper roundly analysed the water vapor, water vapor flux, water vapor budget and rainfall under the background of climate warming, and indicated that the atmospheric circulations of the area were different in dry years and wet years, and also studied the process of water hydrologic cycle. The main conclusions are as follows:(1) The average annual precipitation of Qilian Mountain is 288.3mm from 1960 to 2002, the value is 279.6mm before 1987, and 302.3mm after 1987, which increased by 8.4%.From the whole Northwest area, it is 10% lower than in the west of the Northwest, but -5%~ -15% higher than in the east of the Northwest.(2) The rainfall of Qilian Mountain concentrates in the months from May to September, the precipitation amount of the five months accounts for 86.8% of precipitation of the whole year. And there is less precipitation amount in the other months which accounts for 13.2% of the whole annual precipitation.(3) Under normal situation, there is the water vapor convergence is normal in the low troposphere air of Qilian Mountain. The non- divergence layer fluctuates around the layer of 600hPa, and the rainfall is mainly induced by the water vapor convergence from ground to the layer of 600hPa. Usually the divergence is over the layer of 600hPa in most months of the year. The average annual budget of water vapor is 809×10~8m~3/a.(4) In summer, there is a shear line of water vapor over Tibetan Plateau, and it is the symbol to differentiate wet year or dry year that the Qilian Mountain area locates in the district of shear line or on the brim of it. The Mongolian cyclone and the westward extension place of western Pacific subtropical high are the main atmospheric circulation systems fromMay to September, it is wet year when the Mongolian cyclone is strong and western Pacific subtropical high is eastward, and vice versa.(5) In Qilian Mountain area, the water vapor content increased and glaciers thawed expedited because of the climate warming. At the same time, the wind speed of the area minished and the residence time of water vapor increased, so as to the precipitation increased with the evaporation. Therefore, it can be concluded that the precipitation efficiency heightened, which is the right reason of the precipitation increased after 1987.(6) With the increase of air temperature of the Qilian Mountain because of the global warming, the time of sprinkle in this area was decreasing and that of mid-rain was increasing, but the time of heavier rain changed a little.