基于SPOT-VGT NDVI的西藏羊卓雍错流域地表覆被变化研究

利用1998年—2007年SPOT-VGT NDVI植被指数，分析了羊卓雍错流域NDVI时空变化特征及其与主要气候因子(气温，降水)的相关关系。结果表明：时间上，流域平均NDVI年内季节变化明显，变化幅度在0.12～0.31之间，5月份开始较快上升，最高值出现在9月份。1998—2007年10年间，羊卓雍错流域NDVI的多年平均值为0.19，总体上呈缓慢上升的趋势，表明流域的生态环境有改善的趋势。从空间分布看，NDVI高值区与水源、海拔高度和植被类型有很大关系，在水源附近区域NDVI值相对较高，草甸型草场NDVI值最高。气温和降水是影响流域植被的重要气候因子，在植被生长季节月平均NDVI与上月平均气温和降水的线性相关系数分别为0.7和0.71，近年来流域的暖湿化气候变化趋势有利于流域生态环境的改善。

Vegetation Change of Yamzho Yumco Basin in Southern Tibet Based on SPOT-VGT NDVI

The area we studied is Lake Yamzho Yumco Basin (28°27′-29°12′N, 90°08′-91°45′E), the largest inland lake basin in southern Tibetan Plateau, China. Using the SPOT-VGT NDVI vegetation index from 1998 to 2007 in the basin, the temporal and spatial variation characteristics of NDVI and its correlation with the major climatic factors (air temperature, precipitation) were analyzed. The results show that the average NDVI of the lake basin ranges from 0.12 to 0.31 and its seasonal change is obvious; the NDVI begins to rise rapidly in May and reaches the maximum value in early September. The average NDVI of the basin shows the slow increasing trend during 1998 to 2007, and it indicates that the eco-environment of the basin is recovering. The high value of NDVI has close relationships with water supply, altitude and vegetation types, so NDVI is relatively high near water sources and is the highest in meadow grassland. The summer air temperature and precipitation are the important climate elements that influence the vegetation in the basin, and the linear correlation coefficients between NDVI and air temperature and precipitation are 0.7 and 0.71, respectively. In recent years, warm and humid trend of the local climate is prevailing to improve the ecological environment in YamzhoYumco Basin.