NDVI是表征区域植被覆盖的重要指标。本文把黄河流域划分为 16个区域 ,利用Pathfinder (探路者 )的AVHRR NDVI资料 ,得到各区域 1982～ 1998年NDVI统计序列 ,详细分析了各区域NDVI时空变化特征。研究表明 ,17年来黄河流域各分区年平均NDVI都呈增加趋势 ,说明植被覆盖增加 ,生态环境好转 ,但是 8月份龙羊峡以上和兰河干流区间NDVI则有所下降 ,生态环境有局部恶化趋势。最后研究各区域NDVI与降水、径流和径流系数的年内、年际相关关系 ,结果表明 :从年内变化看 ,黄河流域各区域NDVI变化与降水、径流变化呈明显的正相关 ;从年际变化看 ,黄河流域各区域NDVI波动趋势与降水具有一定的相关性 ,但与径流、径流系数变化的关系相对复杂 ,不具有明显的相关性

NDVI is an important index denoting a region's vegetation cover. In this paper, the Yellow River Basin is divided into 16 sub-regions and their NDVI series of 1982-1998 are obtained from AVHRR-NDVI of Pathfinder. The spatio-temporal changes of NDVI in the Yellow River Basin are analyzed. The results show that:(1) In general, NDVI in all sub-regions reaches peak value in July or August within a year in the Yellow River Basin. In average in the 17 years, the NDVI values show the increasing trends in August and in annual average in other sub-regions except that they show the downward trends in the Sanhua and the above Longyang gorge sub-regions in August. These imply that the coverage percentage of the vegetation presents a rising trend and the ecological quality is being improved on the whole in the Yellow River Basin, but there is some deteriorating trend in some sub-regions in August. (2) With obvious differences in the 16 sub-regions, the higher annual values of NDVI occur in the Taohe, Yiluohe and Weihe sub-regions, while the lower in the indraft area and the Lanhe sub-regions. The spatial changes of NDVI are unanimous with precipitation in most part of the Yellow River Basin, and the average changing rates of NDVI in different sub-regions are different. Finally, the relations of NDVI between precipitation, runoff and runoff coefficient in every sub-region are researched. The results show that NDVI has some apparent positive correlations with precipitation and natural runoff within a year, and furthermore, NDVI has some time lags behind precipitation. From the perspective of inter-annual changes, NDVI has some positive correlations with precipitation, but has complex relations with natural runoff and runoff coefficient variability. There is no, if any, obscure correlations between them.