Land Degradation in the Oases on the South Side of the Taklimakan Desert

塔里木盆地绿洲及其周边地区的年蒸散量存在差异。据计算，和田站年降水量约为25-100 mm，年蒸散量约为100 mm。绿洲潜在蒸散量可达500 mm以上，部分沙漠地区可达1000 mm，塔里木盆地南部绿洲处于25 ~ 100 mm等雨量线之间。北方绿洲多位于25 mm-200 mm等雨量线之间，年蒸散量等值线为100 mm-200 mm;因此，较高的温度仍可能导致蒸散量的普遍增加。目前，沙漠中的河流长度由于流量的波动而逐年变化很大。例如，克里雅河1991年的年径流量为7.0 ×10^8 m^3，其中56%（4.0×10^8 m^3）用于农业灌溉，其余3.0×10^8 m^3用于农业灌溉。 关于我们 克里雅河流域水文条件可分为4个区域：1）上游位于昆仑山，由于支流交汇，河水化学成分纵向变化复杂; 2）中部为冲积扇，克里雅绿洲位于冲积扇底部。在该区域，下游河水的水化学变化非常复杂。3）在下游，蒸发对化学和同位素组成有很大的影响。（4）在克里亚河的最低段，河流的下游水化学变化复杂，地下水化学表现出很大的区域差异，民丰绿洲的灌溉农业一直依赖于从尼雅河引水。少

The annual evapotranspiration varies in and around oases in the Tarim Basin. According to our calculations, the annual precipitation is about 25-100 mm, and annual evapotranspiration is about 100 mm at Khotan station. Since the potential evapotranspiration can reach above 500 mm in the oases, in some desert areas it can reach 1000 mm. The oases in the southern part of the Tarim Basin are located between 25 mm and 100 mm isohyet. Many oases in the northern part are located between 25 mm-200 mm isohyet and experienced 100 mm-200 mm isograms of annual evapotranspiration ; therefore, higher temperatures may still lead to a general increase in evapotranspiration.At present, the length of rivers in the desert changes greatly year by year due to fluctuations in the amount of discharge.For example, the annual discharge of the Keriya River (1991) is 7.0G×10^8 m^3, and 56% of that discharge (4.0×10^8 leaches m^3), is used as irrigation water for agriculture, while the remainder (3.0×10^8 m^3) in … More to the ground, recharging the groundwater annually.The Keriya River basin can be divided into the following four regions by hydrological conditions :1) In the upper part, which is located in the Kunlun Mountains, the longitudinal change in the chemical composition of river water is complicated because of the conjunctions of tributary streams.2) The middle part contains an alluvial fan, on the toe of which the Keriya Oasis is located. In this region, the downstream change in the water chemistry of the river water is very complicated.3) In the lower part, evaporation has a great in fluence on the chemical and isotopic compositions. The river water is more concentrated chemically and isotopically heavier in the lower reach.4) In the lowermost part, where the Keriya River diverges into some channels, the downstream change in the water chemistry of the river is complex and the groundwater chemistry shows a great regional variety.The irrigated agriculture practiced in the Minfeng oasis has relied on water diverted from the Niya river. Less