Spatio-temporal changes of NDVI and their relations with precipitation and runoff in the Yellow River Basin
黄河流域NDVI时空变化及其与降水/径流关系

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.