GIS And SPSS-Based Study Of Space-time Change Of Climate In Three-river-source Area Of Qilian Mountains

The three-river-source area of Qilian Mountains is one of source areas of inland rivers and exorheic rivers in Northwest China. The three-river-source area is located at the meeting place of northeast Qinghai-Tibet plateau and inland arid area in northwest China and holds a very important position in natural geography of China, which makes it typical to study climate in the three-river-source area.The three-river-source area is also a huge and complete ecological system, where the sloping fields with altitude between 2500~3000m are covered with virgin forest and large area of meadow,forming unique water conservation forest in the area. The forest, between the glaciers and the river systems,plays the role of regulating and conserving water source, conserving water and soil, increasing water volume and regulating climate. Therefore, study of climate change in the three-river-source area in Qilian Mountains is of very important significance.This paper makes analysis of the change rate and trend of air temperature and precipitation in Qilian Mountains area on the basis of the highest monthly air temperature, lowest monthly air temperature, and average monthly air temperature and precipitation from the eight meteorological stations in the three-river-source area during 1961~2008, and by taking advantage of climate trend rate method and anomaly method, and analyses air temperature and precipitation cycle in the three-river-source area of Qilian Mountains through MATLAB cycle analysis.From the study it is found that change of air temperature in the three-river-source area in recent 48a presents a trend of notably rising, and the air temperature trend rates of average air temperature, highest temperature and lowest air temperature are 0.40℃/10a,0.18/10a and 0.44/10a respectively, with temperature rise margin: lowest air temperature>average air temperature>highest air temperature, and temperature rise rates in Spring, Summer, Autumn and Winter are 0.58℃/10a, 32.74℉ /10a, 0.35℃/10a and 0.31℃/10a respectively, with the quickest air temperature rise in Spring. Air temperature in the three-river-source area changed from negative anomaly to positive anomaly in late 1980s, change of the average air temperature is characterized by cycles of 20a, 14a and 6a or so,change of the highest air temperature by cycles of 7a and 15a or so,and change of the lowest air temperature by cycles of 12a, 17a and 5a or so. In recent decades precipitation in the three-river-source area has changed greatly, characterized by increase in fluctuation, with average annual precipitation's climate trend rate of 31.55mm/10a. In the three-river-source area the climate trend rates in dry season and wet season are 9.4mm/10a and 29.7mm/10a respectively, and precipitation change cycles mainly include 2~3a, 5a, 7a. 12~13a and 21a or so. In terms of space distribution, the area with years' average highest air temperature and interdecadal average highest air temperature is in the east of the three-river-source area, while the area with the lowest air temperature is in the place centering on Yeniu Ravine; the area with interdecadal average highest precipitation in the east of the three-river-source area,the area with average lowest precipitation in the west. Generally speaking, distribution of precipitation in the three-river-source area is basically the same as that of air temperature and topography, with Qilian area as the rainy and high-temperature center.