The impacts of grassland degradation on regional climate over the origin area of three rivers in Qinghai -Tibet Plateau, China

Regional climate model (RegCM3) was applied to explore the possible effects of land use changes (e.g., grassland degradation in this study) on local and regional climate over the origin area of three rivers (Changjiang, Huanghe, Lancangjiang) in the Qinghai-Tibet Plateau. Two multiyear(1991-1999) numerical simulation experiments were conducted: one was a control experiment with current land use and the other was adesertification experiment with potential- grassland degradation.Preliminary analysis indicated that RegCM3 is appropriate forsimulating land-climate interactions, as the patterns of thesimulated surface air temperature, the summer precipitation, and the geopotential height fields are consistent with the observed values. The desertification over the origin area of three rivers will cause different climate effects in different regions depending on the surrounding environment and climate characteristics. The area with obvious change in surface air temperature inducing by grassland degradation over the origin area of three rivers is located in the Qinghai-Tibet Plateau. A winter surface air temperature drop and the other seasons' surface air temperature increase will be observed over the Qinghai-Tibet Plateau based on two numericalsimulation experiments. Surface air temperature changes in spring are the largest (0.46 ℃), and in winter are the smallest (smaller than 0.03 ℃), indicating an increasing mean annual surface air temperature over the Qinghai-Tibet Plateau. Surface air temperature changes will be smaller and more complex over the origin area of three rivers, with minor winter changes for the regions just outside the plateau and notable summer changes over the north of the Changjang. The reinforced summer heat source in the plateau will lead to an intensification of heat low,causing the West Pacific subtropical high to retreat eastward. This will be followed by a decrease of precipitation in summer. The plateau's climate tends to become warm and dry due to the grassland degradation over the origin area of three rivers.