基于1981~2001 年NOVAA/AVHRR 和1998~2004 年SPOT VEGETATION 归一化植被 指数(NDVI) 数据， 对榆林地区植被动态变化进了定量研究， 并且利用多年气象数据分析了降水 和温度变化情况。结果表明: 榆林地区植被有了明显改善， 其改善状况集中于8、9、10 月份; 植被 覆被变化具有明显的区域差异， 北部植被覆盖改善的趋势明显， 且变化比较平稳; 南部增加趋势 不明显， 有的地方还呈下降趋势， 变化幅度大。

Yulin district is located in the most Northern part of Shaanxi province, between 36°57′and 39°34′N, and 107°28′and 111°15′E. Yulin district is one of the areas of the most serious soil erosion in the world and receives a lot of attention from the Chinese government and international societies. After the establishment of the People's Republic of China, the desertification intensity declined because of rehabilitation measures. However, there is lack of knowledge concerning the dynamics of land cover and the complex role of factors in inducing changes in land cover. In the study, by usage of normalized difference vegetation index(NDVI) as an indicator of vegetation activity, seasonal trends of vegetation activity and their dynamic responses to climate changes in Yulin district were explored based on remotely sensed data (NOAA- AVHRR and VEGETATION) from 1981 to 2004. As a result, spatially averaged seasonal NDVI in Yulin showed a pronounced increase during the last two decades. The average autumn NDVI indicated the most significant increase. By analyzing inter- annual changes in seasonal NDVI, it was found that the advance of growing season was a major way for response of vegetation activity to climate changes and that the way exhibited a large regional heterogeneity. From the southeast to the northwest, change amplitude showed a declining trend.