China has experienced substantial land cover changes for hundreds of years, such as deforestation, agricultural expansion, and urbanization. These land cover changes can modify the physical and thermodynamic characteristics of the land surface, thereby influencing climate at regional or broader scales. In this dissertation, I first examine the performance of state-of-the-art general circulation models to assess their ability to skillfully simulate climate in China. Then, the CESM and WRF models are used to investigate specific biogeophysical effects of land cover changes--including vegetation changes and urbanization. Multimodel ensembles of CMIP5 models are found to well capture the spatial patterns of seasonal and annual temperature and precipitation. However, they contain substantial cold biases over the Tibetan Plateau especially in the cold season, and overestimate precipitation in most regions of China, especially along the eastern edge of the Tibetan Plateau. Four CMIP5 models are identified due to their better simulation of historical surface air temperature variability over China: MPI-ESM-LR, CanESM2, MIROC-ESM, and CCSM4. Focusing on CCSM4, a subset of CESM, sensitivity analyses indicate that, for historical vegetation changes, summer temperatures are regulated by evapotranspiration, which can decrease the diurnal temperature range. Decreases in winter temperature over northern China are mainly influenced by surface albedo changes. Vegetation changes do not exhibit significant impacts on summer precipitation or the East Asian summer monsoon, but could strengthen East Asian winter monsoon and decrease winter precipitation in southern China. When urbanization is included, there are more significant and extensive impacts on temperature and precipitation in China, including greatly increased minimum temperatures and influences on East Asian Monsoon. Future climate projection reveals that urbanization produces strong warming effects, up to 1.9?C at local scales, which is comparable to the magnitude of greenhouse gas forcing under the RCP 4.5 scenario. The impacts of urbanization on precipitation show a combined effect from local moisture deficits and large-scale circulation changes. In summation, land cover changes play an important role in climate over China. Not only vegetation changes, but urbanization also should be included in model simulations to provide realistic and complete climatic impacts of land cover changes.
