Change of Climate and Hydrology in the Tarim River Basin during Past 40 Years and Their Impact

The Tarim Basin is the biggest arid inland basin in China. The Tarim River Basin is located in the southern half of Xinjiang. It is surrounded by mountains on three sides and is a closed-basin with no outlet to the sea. Most of the inner area of the basin comprises the Taklamakan Desert. From the confluence of its three main contributing tributaries, the Tarim River mainstream extends \{1 321\} km to Taitema Lake. There are numerous other rivers coming down from the mountains that disappear into the desert. A number of rivers fed by snowmelt and glacier melt begin in the mountains and drain into the basin with average annual virgin flow of about 35 billion m3. Around the rivers may be found oases of small villages and agriculture.\;The three tributary river systems that contribute flows to the Tarim River (Aksu, Hotan and Yarkant) join just above the Aler gauging station where the Tarim River begins. In addition the Kaidu-Konque River Basin, which is hydrologically separate from the Tarim River, contributes water to the Tarim River by means of a man-made transfer channel. Actual annual contributions under existing conditions are estimated to be 2\^9 billion m\+3 for Aksu, 1\^2 billion m\+3 for Hotan, 0\^1 billion m\+3 for Yarkant, and 0\^15 billion m\+3 for Konque, for a total of 4\^35 billion m\+3. All of this water is consumptively used before reaching the \!green corridor\.\;In past 40 years, last decade (1991\_2000) is the warmest period for mountainous area and wettest period for the plain area, whereas increasing wet of the plain area appeared in last 20 years, and a lighten dry trend in last decade for most part of the plain except Aksu Oasis. A distinct increasing precipitation is in 1990s for most parts of mountains region of Tarim River Basin including the south slopes of the Tianshan and Pamirs, and but a decreasing precipitation zone is in west Kunlun Mountains during last 20 years.\;As the influence of the warm-wet weather on the river resources, the streamflow sourced from the four tributary river systems that contribute flows to the Tarim River (Aksu, Hotan, Yarkant and Kaidu) have a increasing trend in past 40 years, and the total runoff of the Tarim River Basin during the years from 1991 to 2000 increased by 7\^6% of that during the past 40 years. Historical annual flows average over 4 billion m\+3, but for the past two decades there has essentially been no flow below Daxihaizi Reservoir, 300 km upstream of Taitema Lake. This 300 km reach referred to as the \!green corridor\, has thus been without any significant or sustained flow during this 20 year period. Water quantity has been drastically reduced and water quality has deteriorated dramatically in the lower reaches of the Tarim River which have negatively impacted irrigated agriculture and pasture lands.