以乌鲁木齐市2000,2006,2010和2014 年TM/ETM+/OLI影像为数据源,基于NDVI的像元二分模型生成植被覆盖度图,再与ASTER GDEM数据生成的海拔、坡度、坡向图进行空间图像叠加,分析植被覆盖分布特征和变化原因。15年来研究区植被覆盖度总体呈现先整体下降,然后以2006年为拐点显著回升的U型趋势。较2006年,2014年乌鲁木齐县北部和米东区东北部的温带半灌木、矮半灌木荒漠有一定改善;米东区北部温带矮半乔木荒漠和达坂城区的温带丛生矮禾草、矮半灌木荒漠草原改善显著。地形因子和植被覆盖类型影响了植被覆盖水平的分布格局,夏季当月及上月降水量对研究区植被覆盖尤其荒漠草地影响显著,草地与灌丛的变动性大于林地。经济活动与生态工程建设等是植被覆盖变化的驱动因素。荒漠草原覆盖度受自然和人为因子的耦合作用大,应加强保护力度。近年来大规模实施系列林草业工程对全市植被覆盖度提高、生态环境改善起到了重要作用。

Based on four periods of remote sensing images of TM/ETM+/OLI (2000,2006,2010 and 2014) and digital elevation model of ASTER GDEM,the vegetation fractional cover distribution maps in the four periods were got by conducting the pixel dichotomy model using NDVI (Normalized Difference Vegetation Index).Further,the vegetation coverage level maps in the four periods were overlaid with altitude map,slope gradient map and slope aspect map respectively.The map were generated using digital elevation model ASTER GDEM to calculate and analyze the distributions and variations of vegetation cover in the horizontal and vertical direction.Finally the temporal and spatial changes of vegetation fractional cover,the vegetation improvement/degradation and the driving forces were analyzed.Massive degradation and significant improvement like the shape of U and the 2006 as a turning point showed the trends of vegetation fractional cover in the four periods.Compared with 2006,the vegetation cover of temperate semi-shrubby and dwarf semi-shrubby desert region in the north of Urumqi County and in the northeast of Midong District were improved to some extent.And the vegetation cover of temperate dwarf semi-arboreou desert in the north of Midong District and temperate dwarf needlegrass,dwarf semi-shrubby desert steppe in Dabancheng District were improved more significantly in 2014.Therefore,the distributions and variations of vegetation cover in Urumqi city was affected by natural factors such as precipitation,terrain factors (elevation,slope,aspect) and vegetation cover type and so on,as well as anthropogenic factors including economic activity and ecological conservation program.Desert grassland coverage had stronger instability,which was coupled by natural and anthropogenic factors,so we should improve the level of protection.Especially,a variety of ecological protection projects of forestry and grass in recent years in Urumqi city were carried out on a large scale,which played a vital role in the promotion of vegetation fractional cover and improvement of the ecological environment of Urumqi city.