Simulation Study Of Climate Change Impacts On Grassland Productivity In Northern Tibet

Climate change is the current international research hotspots on global change research area. Global climate change will affect greatly environment, ecological and social economics systems. The Naqu prefecture of Northern Tibet is commonly known as the "Weather System Sensitive Spot", the environmental condition of this area has significant effect on the mainly rivers, climate and eco-environment of Tibet and the whole country, so much as the global for the rigorous natural condition and fragile ecosystem. Therefore it is very important to evaluate impact of climate change on grassland productivity and accumulate the basic scientific data of the grassland in Northern Tibet region, which could provide theoretic basis and scientific & technical support for the sustainable utilization, scientific management of grassland resource and the improvement of the grassland eco-environment.The study analyzed temperature and precipitation observed meteorological data from 1966-2003 in Northern Tibet. Based on the remote sensing technology, the grassland productivity of this area was analyzed from 1981-2004. The correlation analysis between temperature and precipitation and grassland NPP was accomplished. The purpose of the study was to explore the impact of historical climate change on grassland productivity. It was groundwork of impact assessment of climate change in the future.Based on historical analysis, impacts of climate change on grassland productivity were evaluated. Firstly, SPUR model was validated using grassland experiment data; secondly, output of PRECIS (Providing Regional Climate for Impact Studies) driven by ECMWF reanalysis data (ERA) were employed to SPUR mode to validate the linkage approach of PRECIS outputs with SPUR model; thirdly, aboveground biomass of Kobrezsia pygmaea and K. humilis and Stepa purpurea grassland were evaluated under A2 and B2 scenarios in 2080s (2071-2100). The main conclusions are as following:1. Historical analysis: In recent 40 years, the tendency of an increase in temperature was significant, annual precipitation fluctuate greatly, it increased evidently since 1990s. In a word, climate trends warming and wetting in Northern Tibet region. Based on the remote sensing technology, the dynamic change of NPP (net primary production) from 1981-2004 in this area indicated: spatial distribution change of grassland vegetation NPP showed horizontal zonal conditions due to water and heat conditions in Northern Tibet; in recent 24 years, the annual mean vegetation NPP of this area is 21.3×10¹²gC·a^-1, it is less than that of Qinghai-Tibet Plateau and other grassland region in China, the annual change of NPP fluctuate greatly, the tendency of NPP is descend. After the correlation analysis between temperature and precipitation and grassland NPP, we found that the impact of precipitation on grassland NPP is greater than that of temperature on grassland NPP. As a whole, the negative impact of regional climate change on grassland vegetation is stronger than the positive impact.2. Validation of linkage approach of SPUR mode and PRECIS output: Comparison between simulation and observation indicated that the approach of PRECIS coupled SPUR model was feasible and could evaluate change of grassland productivity under A2 and B2 scenarios.3. Climate change impacts assessment. Comparing the 2080s(2071-2100) under A2 and B2 scenarios with baseline year(1961-1990), the results of impact of climate change on grassland productivity in Northern Tibet region are as following: (1)Annual average Tmax (daily maximal temperature) increased by 4.92℃～5.35℃(A2 scenario) and 2.33℃～2.65℃(B2 scenario), annual average Tmin (daily minimal temperature) increased by 4.68℃～5.94℃(A2 scenario) and 2.47℃～3.17℃(B2 scenario). Annual average total solar radiation of this area decrease. The tendency of an increase in annual average precipitation was significant in Anduo and Naqu and bange station. (2) Under A2 and B2 scenarios, aboveground biomass of K. humilis and Stepa purpurea grassland would almost increase. Without CO₂ direct effects, aboveground biomass of K. humilis and Stepa purpurea grassland increased by-1.18%～15.74% and 14.94%～34.14% respectively(A2 scenario), increased by 2.05%～14.03% and 14.60%～20.68% (B2 scenario); With CO₂ direct effects, K. humilis and Stepa purpurea grassland increased by 0.86%～18.60% and 14.98%～23.67% (A2 scenario), increased by 0.02%～14.03% and 0.29%～20.91% (B2 scenario). The region where precipitation decrease, aboveground biomass of Kobrezsia pygmaea grassland would decrease. (3) With CO₂ direct effects, CO₂ fertilization effect is not significant, there is no big difference between aboveground biomass with CO₂ direct effects and that with no CO₂ effects. So the grassland productivity in Northern Tibet Region may not benefit from CO₂ fertilization effects.