1994-2016年和田绿洲植被覆盖时空变化分析

监测植被变化对评价区域生态环境质量及生态过程具有重要意义。基于Landsat数据影像，运用归一化植被指数、像元二分模型、重心迁移模型等方法分析和田绿洲植被覆盖时空变化。结果表明：（1）和田绿洲植被分布总体以玉龙喀什河和喀拉喀什河为轴线，从高到低向外展布，高覆被以大面积片状集中于绿洲中部，低、中覆被相对零散围绕高覆被分布；（2）过去23年，和田绿洲植被覆盖面积和植被覆盖度均呈升高趋势。2016年相比1994年，绿洲植被覆盖面积增加553 km²，增长了19.6%；（3）和田绿洲覆被变化存在阶段性和区域性差异。时段上，2000-2005年覆被面积增加最明显；区域上，西部覆被增加最显著；（4）气候变化对和田绿洲覆被变化存在一定影响，但人类活动影响最直接。其中耕地开垦、作物种植是和田绿洲覆被增加的最主要因素，而城市基建是引起绿洲覆被减少的最主要因素。同时，因农耕区水耗增加挤占天然覆被生态用水，引起天然覆被退化，威胁绿洲未来发展；（5）过去23年，绿洲覆被重心整体西移。

Spatio-temporal variations in vegetation cover in Hotan Oasis from 1994 to 2016

It is of significance to monitor the changes in vegetation in the assessment of regional ecological environment quality and ecological process. The typical Hotan Oasis in the arid region of Northwestern China was selected as the study area. Based on Landsat remote sensing images, the temporal and spatial changes in the vegetation cover in Hotan Oasis were analyzed using NDVI, binary dichotomy, and gravity center migration models. The aim of this study was to understand the characteristics of vegetation cover changes in the oasis during recent decades. The results demonstrated that the vegetation distribution in Hotan Oasis is generally distributed from high to low on the axis of Yulongkash and Karakash Rivers. The high vegetation cover is concentrated in the middle of the oasis, whereas, the high vegetation is surrounded by relatively the low and medium vegetation. During the past 23 years, the vegetation-covered area and vegetation coverage of Hotan Oasis have increased significantly. In 2016, compared with that in 1994, the vegetation-covered area has increased by 553 km², an increase of 19.6%. In terms of different levels of vegetation cover changes, high vegetation cover increased significantly, with an increase of 897 km² (83.6%) during the past 23 years. The fluctuation and change in medium vegetation cover were obvious. In 2016, compared with that in 1994, the area decreased by 103 km² (9.3%); low vegetation cover significantly reduced, with a decrease of 241 km² (38%) during the past 23 years. There are time-phased and regional differences in the spatial changes in the coverage of Hotan Oasis. In terms of area change, from 2000 to 2005, the area of oasis vegetation cover increased most obviously. In terms of regional changes, the vegetation coverage in the west and east of the oasis increased most significantly, and the urban areas and nearby areas of Hotan City, Moyu County and Lupu County decreased significantly. The expansion of cultivated land is the main cause of changes in oasis cover. However, the reclamation of natural grassland will reduce the ecological effects of the oasis, which will threaten the ecological stability and sustainable development of the oasis in the long term. As a whole, over the past 23 years, the center of gravity of oasis cover has moved westward.