LAKE EVOLUTION AND CLIMATIC AND HYDROLOGICAL CHANGES IN ARID ZONE OF XINJIANG

Both natural and artificial factors bring effects to lake water resources in the arid zone of Xinjiang. The considerable and frequent shrinkage and expansion of lakes may cause a series of regional environmental problems.However,the influence intensity of the factors on lake variations changes with time. The lake variations were mainly controlled by climatic factors before human society.During the period between 6.5 and 8.0 kaBP,the Ebinur Lake had reached the highest water level in a time span of almost ten thousand years.The average precipitation of the Ebinur drainage area was about 22%,higher than that of the present,and the lakes in other regions were also remained under a high water level.Around the time of Early Middle Ages and the Little Ice Age,humid climate had lasted for a hundred years.Some lakes,such as the Ebinur Lake,Lop Nur Lake,and Bosten Lake,had relative high water level.After the appearance of human society,the influences of human impact on water resources have increased.The strongest human impacts appeared in 1960s and 1970s.As the result,lakes shrank greatly in the plain area of Xinjiang.For example,the lake area of the Ebinur was decreased by about 400 km² compared with that in 1950s.Some big lakes including the Lop Nur,Taitema and Manas Lakes,shrank at a size of 100 km² or more or even dried up sometimes.The Sayram Lake and other mountain lakes,however,remain under the control of climatic factor.They were relatively stable and the changes in size were consistent with the climate change trend.In a long-term perspective,the lake water resources in Xinjiang are mainly influenced by natural factors,and human activities will amplify and accelerate the natural process and cause faster and more frequent lake variation.