中文摘要：

在当前全球变化和人类活动剧烈影响下，研究黄土高原植被覆盖的发展趋势及其与主要限制因子的关系，对黄土高原退化生态系统的恢复和区域生态环境评价有着重要意义。我们利用GIMMS-NDVI数据和长期降雨数据，对黄土高原中部泾河流域22a的植被覆盖时空演变及其与降水的关系进行了研究。结果表明，1）1982-2003年，泾河流域植被覆盖整体呈微弱的增加趋势，并在空间上表现出一定差异。植被覆盖增加的地区约69．62％，其中显著增加的地区16．61％，主要分布在泾河流域的中西部和下游小流域，显著下降的地区约1．65％，主要分布在泾河流域上游及周边地区；2）NDVI与降水极显著相关。年NDVI随年降水服从对数分布，生长季（4～11月）NDVI比降水滞后1个月；3）泾河流域降水利用效率不稳定变化，土地退化状况未见有效改善，并且泾河流域降水利用效率随降水量的增加而降低，值得探索。

英文摘要：

Aim Vegetation and environmental degeneration from global change and intensive human activities are among the most serious problems on the Loess Plateau of China. Our objective was to study the trend in vegetation cover and its relationship with dominant environmental factors to provide a basis for ecological restoration and regional assessment on the Loess Plateau. Methods We analyzed the temporal and spatial changes of vegetation cover and its relationship with rainfall in the Jinghe Watershed using the GIMMS-NDVI time series data and rainfall data for 1982-2003. Important findings Annual NDVI slightly increased during the study period and varied spatially. Vegetation cover increased 69.2%, of which the 16.61% of the study area in the middle-west and lower reach of the watershed had a significant increase of vegetation cover. NDVI strongly decreased in the upper reach and the surrounding area, which accounts for 1.65% the whole watershed. NDVI was highly correlated with precipitation, and annual NDVI and annual rainfall had logarithmic distributions. There was a one-month lag of monthly NDVI after rainfall in the growing season. Rain use efficiency （RUE） decreased during the study period, which indicated lack of improvement of the land situation. Our find- ing that RUE decreased with increased precipitation contrasts with previous research.