Relationship Between the Fractional Vegetation Cover Change and Rainfall in the Yellow River Basin
黄河流域植被覆盖度动态变化与降水的关系

Vegetation plays an important role in the energy, matter and momentum exchange between land surface and atmosphere and the change of vegetation is mainly caused by climate variation and human activities. Therefore, it is necessary to study the relationship between climate factors and inter-annual change of vegetation, which will help us to understand global change. In order to understand the effects of rainfall on vegetation cover, we selected the Yellow River Basin in China as the study area to assess the inter-annual change of fractional vegetation cover in the Yellow River Basin, and analyzed the relationship between rainfall and fractional vegetation cover using 8 km resolution multi-temporal NOAA AVHRR-NDVJ data from 1982 to 1999. The data are from NASA Pathfinder AVHRR Land data sets. The spatial distribution and dynamic change of fractional vegetation cover were studied by using yearly maximum NDVI. The results show that in spite of inter-annual fluctuations, there exists an inclining trend of fractional vegetation cover for the whole basin, which is different from the trend of annual rainfall. The inclining trend may be caused by human activities while inter-annual fluctuation may be caused by climate factors. Finally, the correlation coefficients between NDVI and rainfall in different periods (annual rainfall, rainfall in flood and non-flood seasons) were computed for every pixel to assess the effect of rainfall on fractional vegetation cover change. The results show that there is good relationship between NDVI and rainfall in the Yellow River Basin, especially in arid and semi-arid steppe zones, and inter-annual change of fractional vegetation cover is mainly affected by flood season rainfall. However, human activities can reduce the effect, for example, the effect of rainfall on NDVJ is small in irrigated cropland.