Estimation of the Water Resources Affected by Climatic Warming and Glacier Shrinkage before 2050 in West China
SHI Ya feng (Cold and Arid Regions Environment and Engineering Research Institute, CAS, Lanzhou Gansu 730000, China)
According to a comprehensive prediction with some uncertainties, temperature of the Tibetan Plateau may rise by 2.5 ℃ by 2050 or so as compared to that at the end of the 20th century. It is very likely that the summer temperature, which causes intense ablation of glaciers, will rise by 1.4 ℃. As a result, the equilibrium line altitude will rise more than 100 m; the ablation in the tongue zone will exceed the ice amount moved from the accumulation zone; and glaciers will thin and retreat. In the earlier stage, thinning prevails and meltwater increases. While in the later stage, glacier largely shrinks, meltwater decreases and some glaciers will disappear. There is a large difference in the sensitivity of response of glaciers to climate warming, depending on the size and type of glaciers. Using the statistical data of China's glacier inventory, several regions were selected to make a prediction of the water resources affected by glacier shrinkage before 2050. In some regions, such as the Hexi Region in the north slopes of the Qilian Mountains, southern margin of the Junggar Basin in the north slopes of the Tianshan Mountains and the Hami-Turpan Basin in the south slopes of the Tianshan Mountains, glaciers, most of them have an area less than 2 km 2,are sensitive to the climate warming and hence ablation increases. At the beginning of this century meltwater will reach its peak value, and by the middle part of this century meltwater will decrease. The impact on runoff of different rivers is estimated to be in the order of 10 6～10 7 m 3·a -1 . Some basins, such as the Shule River Basin in the Qilian Mountains and the Manas River Basin in the Tianshan Mountains, meltwater can account for one-third or more of the river runoff. It is predicted that several medium-sized glaciers of 5～30 km 2 will reach their meltwater peak value by the middle part of this century and their meltwater will increase in the order of 10 8 m 3·a -1 . In the mountain regions around the Tarim Basin there are totally 22 009 km 2 of glaciers, 22 larger ones of which have an area exceeding 100 km 2,with their tongues covered by thick debris mantle. Therefore, these glaciers will retreat slowly. Glacier meltwater occupies 50%～80% of the discharge of the Yarkant River, Yurunkax River and Aksu River. At present the main stem of the Tarim River is mainly fed by meltwater of glaciers in the southwest part of the Tianshan Mountains via the Aksu River. It is predicted that glacier meltwater will continue to increase before 2050, the increased volume may reach about 25%～50% more than that at the beginning of this century, and annual increased discharge of 7 major rivers of the Tarim Basin is estimated to be in the order of 10 8 m 3·a -1 . In order to effectively utilize the increased meltwater, it is necessary to construct mountain reservoirs to increase energy output and irrigation effect. Inland watersheds in the Qaidam Basin and the Tibetan Plateau are dominated by extreme continental type glaciers with lower temperature and slow retreat velocity. Temperature rise and meltwater increase during the first half of this century are favorable to the development of animal husbandry and economic growth. However, in the maritime-type glacier regions at the southeast part of the Tibetan Plateau and the Hengduan Mountains, where precipitation is more and ice temperature is higher, the temperature rise will quicken ablation and retreat of glaciers, perhaps thus causing frequent flood and debris flow disasters.