中文摘要：

榆林地区位于我国农牧交错带，能源富集区，生态环境脆弱。建国以来的土地整治工作取得显著成效。本文利用1998—2004年SPOTVEGETATIONNDVI分析了榆林地区植被变化情况。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状况有明显改善，改善集中于8、9、10月份。而且植被覆盖变化具有明显的区域差异，北部植被覆盖改善趋势明显，且变化平稳；南部增加趋势不明显，有的地方还呈下降趋势，变化幅度大。

英文摘要：

Yulin district is located in the most Northern part of Shaanxi province. The landform is compromised of two parts ： the sandy land lies in the northern part, accounting for 48.3 % of the total area, while the hilly and gullied region lies in the middle - south which is 51.7% of its total. 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. In the study, using 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 were explored based on remotely sensed data （ VEGETATION ） from 1998 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 interannual 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.