Comprehensive Evaluation of Environmental Effects from Land Change in Hotan Oasis,Xinjiang

[Objective] This study aimed to evaluate the environmental effects coming from land changes in Hotan oasis during 1980-2010. [Method] Based on the Driving Force-State-Response model, expert weight method and entropy method were used to determine weight, and then the composite indexes of environmental effects （CIE for short） were calculated. [Result] During the period from 1980 to 2010, CIE had presented a rising trend whether expert weight method or entropy method in the study area, while the CIE presents downtrend basically in lower reaches. [Conclu- sion] It was the arable land expansion in middle reaches that led to serious land degradation in lower reaches, and may endanger ecosystem safety in Hotan River green corridor. Therefore, it is suggested that the agricultural land use should be restructured, such as reducing the sown areas of some crops with large amount of water consumption. Meanwhile, the effective measures should be taken to distribute water resources and utilize them reasonably. In addition, the oasis-desert ecotone, as well as the groundwater resources, should be also protected.

Assessment of Ecosystem Services Value in Hotan Oasis, Xingjiang

[Objective] The study aimed to assess the ecosystem services value in Hotan Oasis, Xingjiang. [Method] The visual interpretation method was adopted to process TM/ETM＋ images based on field investigation in Hotan Oasis. These inter- pretation data, along with two periods of land use data, were reclassified to farm- land, forest, grassland and so on. Then, the ecosystem services value was calculat- ed and analyzed. [Result] Analysis indicated that the ecosystem services value had been increased by 30.44x108 Yuan （16.51%） in the study area during 1980-2010, which can be explained by the increase of glacier and snowfield distributed in the south mountain with the increase of annual precipitation. At the same time, the con- tribution rate of grassland to ecosystem services value had been decreased as a result of degradation of grassland and occupation from farmland. For the whole basin, the increase of ecosystem services value came from the upper reaches, while the ecosystem services value had been reduced in the middle and lower reaches. In the middle reaches, the reduction came mainly from wetland （-1.83x10s Yuan）, waters （-1.68x10s Yuan）, forest （-0.86x108 Yuan） and grassland （-0.80x108 Yuan）. But in the lower reaches, the ecosystem services values of waters, grassland and forest were -0.61 x108 Yuan, -0.24x108 Yuan, and -0.07x10s Yuan, respectively. [Conclusion] If some effective policies, such as the implementation of returning farm- land to forest and ceasing from farming to grazing, would be taken, the ecosystem degradation can be constrained and reversed in the northwest arid region.

The Estimation of Water Supply and Demand in Hotan Oasis

[Objective] The purpose of this study is to estimate water supply and demand, which can provide a basis for how to allocate rationally water resources in Hotan Oasis. [Method] The water supply and demand in Hotan Oasis in the next15 years were calculated according to water-soil balance. [Result] When the runoff of Hotan River is at a probability of 50%（P=50 for short）, the total water resource is 50.57×10^8m^3, and there is only 33.13×10^8m^3available for social and economics,but there would be a need of 33.44×10^8and 36.06×10^8m^3, and the water shortage would be 1.31 ×10^8and 2.93 ×10^8m^3in 2020 and 2030 respectively. When P =75,the total water resource is 44.30×10^8m^3, there is only 29.39×10^8m^3water available for social and economics. However, there would be a need of 31.43 ×10^8and33.11×10^8m^3, and the water shortage would be 2.04×10^8and 3.72×10^8m^3in 2020 and 2030, respectively. [Conclusion] The problem of water shortage would be serious over the next 15 years, and the fragile ecosystem would be destroyed dramatically with the large-scale land reclamation against natural laws. Hence, the effective policies and measures should be taken timely to prohibit reclamation and to cope with ongoing water shortage, based on the water supply and demand estimation under the background of climate change.

The Estimation of Cultivated Land Threshold Value in Hotan Oasis

[Objective] Water shortage is a key natural factor limiting arid economic development and ecological security.However,the large-scale land reclamation against natural laws has been speeding up water consumption,and the ecological water use which is the primary condition for maintaining ecological security was squeezed.Moreover,the fragile oasis ecosystem would be destroyed dramatically.In order to maintain ecological security,it is urgent to evaluate the threshold value of cultivated land.[Method] The method of water-soil balance was used to evaluate the threshold value of cultivated-land on the premise of allocating downstream ecological water demand.[Result] Under the frequency of 75%（P =75 for short） in Hotan River,the threshold value of cultivated-land in Hotan Oasis would be 13.83×10^4,16.78×10^4and 16.50×10^4hm^2in 2010,2020 and 2030 respectively.Under the frequency of 50%（P=50 for short）,the threshold value of cultivated land in Hotan Oasis would be 14.95 ×10^4,18.08 ×10^4and 17.78 ×10^4hm^2in 2010,2020 and 2030 respectively.If effective measures are not taken to control cultivated-land expansion,the cultivated land area will be 2.78×10^4and 5.07×10^4hm^2more than the threshold values of cultivated land at P =75 in 2020 and 2030 respectively.Even if the efficient water-saving technique are adopted,the water requirement of crop use will increase from 19.77×108to 20.82×108and 21.95×108m3during 2010-2030,and then the ecological water use cannot be guaranteed.[Conclusion] The cultivated-land expansion would threaten the ecological security in Hotan River and Tarim River.Therefore,some strict measures should be taken to protect desert-oasis ecotone,an important constituent of oasis ecosystem which has vital role in maintaining the stability of oasis,and to prohibit cultivated-land expansion.