Responses of net primary productivity of natural vegetation to climatic changes in the source region of the Yellow River

Based on observational climatic data of monthly average temperature,maximum temperature,minimum temperature,relative humidity,precipitation,wind speed and sunshine duration in the source region of Yellow River in 1959—2008,the net primary productivity(NPP) for 50 years was computed with the application of revised Thornthwaite Memorial Model.In addition,the inter-annual change and the seasonal difference of NPP were analyzed,and the responses of net primary productivity to climatic changes was discussed as well.The main results were as follows: In 1959—2008,the annual NPP in this region had an increasing trend,with a linear fitting rate of annual NPP change curves being 95.502~190.72 kg/(hm2·10a),the NPP appeared a high rate mostly after 1990s.The cold and dry climate occurred in the 1970s,the NPP of which was 1.1%~2.1% less than the annual average NPP;and the warm and wet climate appeared in 2001—2008,the NPP of which was 1.1%~2.1% more than the annual average NPP.The main factors which influenced the NPP were precipitation,maximum evapotranspiration and average minimum temperature.The warm and wet climate benefited the growth of the NPP with an average increment of yield by 5.5%~8.5% in the source region of the Yellow River,while the cold and dry climate had an adverse impact on NPP with an average reduction of yield by 5%~9%.If the future climate in the region would become warm and moist,the NPP could increase by 7%~17% in 2050.