中文摘要：

利用GIMMS／NDVI数据分析了中国西北地区1982—2006年植被覆盖时空变化特征及其驱动因子。近25a来，中国西北地区年均植被NDW增速为0．5％／10a，并存在明显的空间差异。天山、阿尔泰山、祁连山、青海的中东部等地区植被NDVI显著增加；青海南部地区、陕西和宁夏交界地区、甘肃的部分地区以及新疆的塔里木盆地、吐鲁番、塔里木河、托里等地区植被NDVI下降。从不同植被类型来看：林地、草地和耕地的年均NDVI都在提高。研究表明：中国西北地区植被NDVI变化是各种自然和人为影响因素综合作用的结果。自然植被（林地等）变化更大程度上反映了气候变化对植被的影响，而人工植被（耕地等）变化更多体现的是人类活动的作用。不同高程、坡度、坡向上的植被NDVI变化存在较大差异，当海拔超过4000m时，植被NDVI增加趋势很小；坡度低于25°的坡地植被NDVI增加主要是由于近年来的植被建设；阳坡植被变化比阴坡活跃，植被改善趋势较强。植被NDVI与气温、降水的年际变化整体上都呈弱的正相关，温度上升使蒸发量增大，促进了土壤的干化，不利于植被生长，并且灌溉农业区的河水灌溉会降低农业植被NDVI和降水的相关程度。农业生产水平和植被生态建设等人类活动对西北地区植被NDVI增加起重要作用。

英文摘要：

In this paper the spatio-temporal variation of vegetation cover in northwest China and its driving factors were analyzed with the average method, trend line and correlation analysis during 1982 to 2006 using GIMMS/NDVI data. The annual average NDVI has been increased with a rate of 0.5 %/10 a in northwest China and there is an obvious difference in the space. The trend line slopes of NDVI were higher than 0. 000 5 in the Tianshan and Ahay Mountains of Xinjiang, the Qilian Mountains of Gansu and the eastern part of Qinghai , and it indicated the vegetation cover was significant increased in these areas. The trend line slopes of NDVI were lower than - 0. 0005 in the southern region of Qinghai, Shaanxi and Ningxia border region, parts of Gansu and Tarim Basin, Turpan, Tarim River, Tuoli in Xinjiang, and it indicated the vegetation cover was declined in these areas. The NDVI of woodland, grassland and cultivated land had an ascending tendency during the study cover change was caused by both natural and human activity in northwest period. Studies show that the vegetation China. The natural vegetation （forests, etc. ） change was influenced by climate change, while human activity was the main reason to change the artificial vegetation （cultivated land, etc. ）. The vegetation cover change for different elevation, slope, and aspect was quite different. When the elevation was exceeded 4 000 m, the NDVI increasing trend was very low; the ecological construction project increased the NDVI at the slope of less than 25; the NDVI on sunny slope was c than that on shady slope. The temperature rose significantly in past 25 years in northwestern China by hanged stronger an average rate of 0.67 ℃/10 a, and precipitation increased by an average rate of 8.15 mm/10 a after 1986. It was positive correlation between vegetation cover and temperature and precipitation annual changes. Temperature rising increases evaporation and promotes drying of the soil, which is not conducive to vegetation growth , and the irrigation in the i