Change feature of net primary productivity of natural vegetation and its impact factors over the source region of the Yangtze River in recent 50 years

Based on climatic observational data of monthly average temperature,maximum temperature,minimum temperature,relative humidity,precipitation,wind speed and sunshine duration in the source region of the Yangtze River in 1959-2008,the net primary productivity(NPP) of natural vegetation was computed by using revised Thornthwaite Memorial Model.The inter-annual change and the seasonal difference of NPP were analyzed,and the impact climatic factors for the change trend of NPP were discussed.The main results were as follows: In the period of 1959-2008,the annual precipitation in this region had an increasing trend,with a linear fitting rate of the annual precipitation change curves being 5.685~13.047 mm?(10a)-1,higher increasing rate appeared in spring and summer;while the annual temperature as well displayed an ascending trend,with a linear fitting rate of the annual temperature change curves being 0.240~0.248 ℃?(10 a)-1,higner ascending rate appeared in autumn and winter;likewise,the annual maximum evapotranspiration(ET0) displayed an ascending trend,with a linear fitting rate of the annual ET0 change curves being 5.073~5.366 mm?(10a)-1,the rate of increasing appeared higher in spring;the surface humid index too displayed an ascending trend,with a linear fitting rate of the surface humid index change curves being 0.013~0.020(10 a)-1,the rate of increasing appeared higher in winter.6~8 climatic periods of Dry-wet alternation happened in 10a period of Temporal frequency,which were the light wet stages since 1990s,while the light dry stages appeared in 1998-2005 at a low frequency.The annual NPP in this region had a significant increasing trend,with a linear fitting rate of the annual NPP change curves being 97.901~197.01 kg·hm-2·(10 a)-1,the NPP appeared in 2001-2008.The main factors which influence the NPP were precipitation,the maximum evapotranspiration and the average minimum temperature.