Fluctuations of Glacier Mass Balance in Watersheds of Qilian Mountain and Their Impact on Water Resources of Hexi Region

In inland watersheds on north slope of Qilian mountain, there are \{2 166\} existing glaciers with a total area of \{1 308\} km 2 and ice volume 60 km 3 . Melt water of these glaciers from year to year feeds to river, and annual recharge reach up to about 8×10 8 m 3 \5a\+\{-1\}, constitute about 11% of total runoff in surface water resources of Hexi region. Using method of statistical mechanics and maximum entropy principle, we obtain that distributions pf precipitation, mean depth and coefficient of runoff in a watershed can be described by a negative exponential function. In a high mountains basin with partial glacier cover, the maximum distributive area of precipitation, depth and coefficient of runoff is glacierized area. In this case, a calculation method of average mass balance for glaciers in a watershed has been suggested. The calculation method is employed to recovery of mass balance for glaciers in the Qilian Mountains. In the past 40 years, glacier changes in eastern section and west section of Qilian Mountains present a spatial variation: Glacier mass balance in Shiyanghe drainage basin of east section has a signification negative balance, \%B \% n in \{-80\}～\{-120\} mm;In Shulehe, Taolehe and Danghe watersheds of west section, glacier mass balance have a characteristic of positive mass balance, \%B \% n at \{+50\}～\{+90\} mm; In Heihe watershed, glacier mass balance get off to transition zone, average mass balance for many years at \{-40\}～\{+40\} mm. Variance in glacier mass balance influence directly to variance in river runoff, \%B\% n and runoff has a negative correlation relation. Difference of glacial size in different watershed will effect to vary of glacial melt water supply rate. Glacial melt water supply rate in Hongshuibahe, Danghe and Changmahe watersheds are in more than 30%～40%; Dongdahe, Dazhemahe, Mayinghe and Taolehe watersheds in 12%～14%; and Xiyinghe and Liyuanhe watersheds have just about 7%. Year to year change of glacier mass balance shows that glaciers in 1950s\_1970s presented a predominating negative mass balance, and from 1980s glacier mass balance begin inverting to positive statue and in 1990s mass balance predominating with positive, is a result of air temperature rising in winter induced increasing of snow fall. Under scenario of global air temperature warming, future glacier mass balance in eastern section of Qilian mountain will trend to increasing, and but glacier mass balance in western section would trended descending, and result in runoff increasing of glacial melt water alimentative rivers in western section, whereas runoff declining apparent of Shiyanghe watershed in eastern section.