Glacier Area Changes In The Qilian Mountains,China

The Qilian Mountains are located in the arid and semiarid regions of northwestern China. It is an important ecological barrier, a transition zone between subcontinental glaciers and extreme continental glaciers, and the birthplace of modern glacier research in China. Studying glaciers in this area not only has a scientific significance, but also has ecological and social importance.Landsat TM, ETM+images were used with the help of digital elevation models and the first Chinese Glacier Inventory data to delineate the outlines of glaciers in the whole area in1990,2000and2010. Spatial distribution and variation characteristics of the glaciers were analyzed. Combined with our own results and previously published results, we calculated glacier area change information in China during the past half century. Then we analyzed the spatial and temporal characteristics of glacier area changes in China, and the trends in temperature, precipitation and freezing level from1961to2010. We also analyzed controlling factors of glacier area changes and time lag between glacier area changes and temperature changes. Based on the results of time lag analysis, we established an empirical model to predict glacier area changes. Finally, using the empirical model, we projected glacier area changes in the future. The main conclusions are as follows:(1) Characteristics of glacier distribution in the Qilian Mountains:the pattern of glacier area distribution with elevation was similar to the shape of normal distribution and the peak was at approximately5,000m; glaciers were distributed mainly in the north-facing aspect; glacier areas increased relative to their size class; more glaciers were distributed in the western portion than in the eastern portion of the study area.(2) Characteristics of glacier changes:glaciers shrank22.38±3%in the Qilian Mountains from1990to2010and the shrinkage accelerated during the second decade; glaciers shrank faster at lower elevations than at higher elevations; glacier shrinkage accelerated below5,000m and slowed down above5,000m; glaciers shrank faster in the south-facing aspect than in the north-facing aspects while maximum shrinkage occurred in the southwest aspect; smaller glaciers shrank faster than larger ones, and the shrinkage accelerated among all the size classes from2000to2010; glacier shrank faster in the eastern portion than in the western portion of the study area; glaciers shrank30.36%with an annual change rate of0.56%in the Qilian Mountains from1956to2010; glaciers shrank15.7%with an annual change rate of0.33%in China from1963to2010; glaciers shrank faster in the peripheral areas than internal areas of the Tibetan Plateau during the past half century.(3) Controlling factors of glacier area change:temperature was the main controlling factor of glacier area change in the Qilian Mountains during the period of1956-2010; temperature was the main controlling factor of glacier area change in China during the period of1963-2010; increasing temperature played an important role in accelerating glacier area shrinkage in ablation zones from2000to2010, while increasing precipitation compensated for melting caused by increasing temperature, resulting in reduced shrinkage in accumulation zones; since glaciers in the eastern portion of the Qilian Mountains were small, at low elevation and subcontinental type, they shrank faster than in the western portion; rising temperature accompanied by other factors caused faster glacier shrinkage in the peripheral areas than in the internal areas of the Tibetan Plateau in China during the past half century.(4) Time lag between glacier area change and temperature change:glacier area change lagged10years behind temperature change in the Qilian Mountains; glacier area change lagged between8to10years behind temperature change in China.(5) Prediction of glacier changes:glaciers in the Qilian Mountains are projected to shrink at an average rate of17%by2030and37%by2050compared to2010; glaciers in China are projected to shrink at an average rate of14%by2030and29%by2050compared to2010.