The Impacts Of Land Cover Change On Regional Climate Over Sanjiangyuan Region In Qinghai-Tibet Plateau, China

Land use/land cover change (LUCC) and its impacts on climate changes have been recognized by the International Geosphere-Biosphere Programme (IGBP) as a key research item for better understanding of the climate variability. Over the last two and half decades, the scientific community has made notable efforts in understanding land use/land cover change as a part of the climate system. Land use change influences the climate variability through changes in surface albedo, land roughness, soil hydrological and thermal features. Human-induced land use changes and the resulting alterations in the ground surface features are poorly recognized drivers of the long-term global climate patterns. Therefore, further research will be necessary for further understanding of the effects of land use/land cover change on climate changes. Sanjiangyuan region (31°39'N～36°16'N, 89°24'E～102°23E) is the source of the Yangtze River, the Yellow River and the Lancang River, located in the Qinghai-Tibet Plateau, south of Qinghai province. Its eco-environment is very sensitive and vulnerable. Sanjiangyuan region as the research object, the impacts of land cover/use change on regional climate and its eco-environment effects are discussed in this paper. Some interesting conclusions can be summarized as:1) Sanjiangyuan region is an important ecological function area for the Qinghai-Tibetan Plateau as well as the middle and lower reaches of rivers originating from Sanjiangyuan region. In recently years, deterioration of the eco-environment, grassland degradation and desertification in the Sanjiangyuan region are very serious because of unreasonable exploitation of the natural resources and rapid growth of the population.2) Based on monthly mean, maximum, minimum air temperature and monthly precipitation data from meteorological stations in Sanjiangyuan region from 1960 to 2005, the spatial and temporal patterns of climate change in this region were analyzed. There is an obvious ascending trend for the interannual variation of air temperature in the study region.The rate of increasing air temperature is 0.299°C/10a, which obviously exceeds those for China and the global mean in the same period. It is proved that Sangjiangyuan region is sensitive to the global climate change. The summer precipitation shows a decreasing trend but is not statistically significant.3) Quantitative evaluation of the climate changes caused by the land use change is very difficult because long-term meteorological and land surface observational data are usually not available and furthermore, the land-atmosphere interactions arehighly nonlinear. A possible solution is to use the regional climate model (RCM) in exploring the interactions between the land use change and the climate change. RegCM3 works well in simulating the basic features of the climate in the study region.4) The grassland degradation in the Sanjiangyuan region can significantly affect the surface air temperature, summer precipitation in China. The notable climate changes take place in the Qinghai-Tibet Plateau and its downstream regions. In the Qinghai-Tibet Plateau, the warming (range from -0.03°C to 0.45°C for multi-year monthly mean, 0.134°C for multi-year annual mean) and drying (up to -0.5mm/day) induced by the grassland degradation over the Sanjiangyuan region can be identified.5) The grassland degradation in the Sanjiangyuan region results in the weakening of the East Asia summer monsoon in China, which will be responsible for the decreasing of the summer precipitation.6) To detect the effects of climate change on eco-environment in Sanjiangyan region, the dynamic changes of both NDVI and runoff as well as the relationship between runoff, NDVI and climate factors are discussed. The analyses indicate that climate change, especially precipitation, is an important driver of runoff and NDVI. Our research demonstrates that the land use/cover changes not only influence regional climate, but also cause runoff and NDVI variabilities.The influences of the grassland degradation on regional climate variability are very complex because of the diversiform interactions between the land surface and the atmosphere, which are different from place to place and is due to different scales of study region, and different seasons as well. Some valuable conclusions have been drawn in the current research, which will be greatly important for further understanding of and better insight into the possible role of the land use changes in the current global warming. Even so, however, detail and further researches in the near future are still necessary because different scales of the land use change will have different effects on regional climate changes. Furthermore, the results may be sensitive to the parameterization schemes of various physical processes, and the proper validation and modification of parameterization schemes based on observed records in the study domain are also needed.