Response of net primary productivity on climate change in the Yellow River Basin

Net primary productivity (NPP) is important in the global carbon budget. The change of NPP can be a good indicator of climate variation to some extent. Therefore, it is necessary to study the relationship between climate factors and inter-annual change of NPP, which will help us to understand global change. An empirical exponential model between NPP and integrated NDVI in the Yellow River Basin in China has been established. The spatial distribution pattern and dynamic change of annual NPP from year 1982 to 1998 are analyzed by using multi-temporal 8 km resolution AVHRR-NDVI data. The results show that there exists an incline trend of mean NPP for whole basin while the rainfall decreases slightly, which demonstrates that human activity effects the vegetation cover and NPP much. Finally, in order to analyze the effect of rainfall and temperature on inter-annual change of NPP, correlation coefficient between rainfall, temperature and NPP are computed respectively. It is found that relativity between rainfall, air temperature and NPP is complicated for different climate and vegetation zone. NPP is not highly correlated with climate factors in most places, which may be caused by human activity and other factors. The effect of rainfall on NPP is significant in desert steppe region, while the effect of temperature on NPP is significant in alpine vegetation region and Qinhai-Xizang Plateau. The correlation coefficient between NPP and temperature is negative in area where NPP is positively correlated with rainfall, while it is positive in area where NPP is negatively correlated with rainfall.