中文摘要：

基于MODIS-NDVI数据，辅以线性趋势分析、Hurst指数及偏相关系数等方法，本文从三个尺度分析了近12年三江源区植被覆盖时空变化特征、未来趋势及其驱动因素。结果表明：（1）近12年三江源区植被覆盖呈现增加趋势，增速为1．2％／10a，其中长江源区、黄河源区植被均呈增加趋势，而澜沧江源区植被呈下降趋势。（2）三江源区植被覆盖具有显著的区域差异，且NDVI频度呈现“双峰”结构。（3）近12年三江源区植被覆盖呈增加趋势和减少趋势的面积分别占64．06％和35．94％，且表现为源区北部增加、南部减少的空间格局。f4）三江源区植被变化的反向特征显著，植被变化由改善趋势转为退化趋势的区域主要分布在长江源区和黄河源区的北部，而由退化趋势转为改善趋势的区域主要分布在澜沧江源区。（5）三江源区植被对降水和潜在蒸散的响应存在时滞现象，而对气温的响应不存在时滞现象。（61三江源区植被覆盖的增加主要归因于气候暖湿化以及生态保护工程的实施。

英文摘要：

The Three-River Headwater Region is the source areas of the Yangtze River, the Yellow River, and the Lancang River. The region is not only of key importance to the ecological security of China. Due to climate change and human activities, ecological degradation occurred in this region. Therefore, ＂The nature reserve of Three-River Source Regions＂ was established, and ＂The project of ecological protection and construction for the Three-River Headwater Nature Reserve＂ was implemented by Chinese government. This study, based on MODIS-NDVI and climate data, aims to analyze the spatial-temporal changes of vegetation coverage and its driving factors in the Three-River Headwater Region between 2000 and 2011 from three dimensions. Linear regression, Hurst index and partial correlation analysis were employed. The results showed that： （1） In the past 12 years （2000-2011）, the NDVI of the study area increased, with a linear tendency being 1.2%/10a, of which the Yangtze and the Yellow river source regions presented an increasing trend, while the Lancang River source region showed a decreasing trend. （2） Vegetation coverage presented an obvious spatial difference in the Three-River Headwater Region, and NDVI frequency was featured by a bimodal struc~re. （3） The vegetation coverage improved area was larger thhn the degraded area, being 64.06% and 35.94% respectively in the 12 years, and presented an increase pattern in the north and a decrease one in the south. （4） The reverse characteristic of vegetation coverage change is significant. In future, the degradation trends will be mainly found in the Yangtze River Basin and north of the Yellow River, while the improving trend areas are mainly distributed in the Lancang River Basin. （5） The response of vegetation coverage to precipitation and potential evapotranspiration has time lag, while the temperature does not have. （6） The increased vegetation coverage is mainly attributed to the warm-wet climate change and the implementation of the e