Sensitivity Experiment On Impacts Of Large-scale Urbanization On East Asian Monsoon And China Climate

By using the global atmospheric circulation model CAM4.0including the Community Land Model CLM4.0and urban canopy parameterization scheme, the possible impacts of large-scale urbanization over eastern China on East Asian monsoon and China climate was investigated via idealized experiments (turning half of regions in the eastern China to urban). This study is an attempt for the studying of the effects of large-scale urbanization and the large-scale effects of urbanization. The main conclusions are as follows:(1) The massive urbanization process over the eastern China lead the land surface temperature and the air temperature over that region to warm significantly, but the responses differ from one time to another. The surface temperature increases most evidently, and the warming amplitudes are2.8℃in winter and3℃in summer; Regarding to the amplitude of warming, the air temperature is smaller than the surface temperature, and in winter is2.5℃but2.25℃in summer; The daily minimum temperature and maximum temperature also rise significantly in winter and summer, and the warming of the daily minimum temperature is more obvious than daily maximum temperature in summer, but in winter the result is opposite; Meanwhile, the urban heat island also changes a lot, and the strength of the urban heat island is0.4℃in winter but0.36℃in summer.(2) Significant changes in the surface energy balance occur over eastern region of China, and the strength differs from time. The net upward long-wave radiation and surface sensible heat flux in winter and summer are markedly enhanced, while the changes of the net surface shortwave radiation are relatively small, the latent heat flux decline significantly in summer but don’t change much in winter; Changes in the energy balance over surface caused by the massive urbanization significantly enhance the surface heating to the atmosphere.(3) Changes in the energy balance over the surface and the abnormal heating from surface to the atmosphere have a large impact on the East Asian monsoon circulation. The large-scale urbanization in the eastern China, will enhance the monsoon in June but weaken the summer monsoon in July and August, while the East Asian winter monsoon will be weakened, but in the Northeast China the East Asian monsoon is enhanced in winter. Overall, the significant effects of urbanization on the East Asian monsoon circulation are mainly in the middle and low level.(4)With the extensive urbanization in the eastern China, the precipitation will increase in the northern China but reduce in the southern China in June. Form the Northeast China to the northern part of the North China the rainfall increases, and from Huanghuai Valley to the southern part of the North China the rain reduces, but in the middle and lower reaches of the Yangtze River to the South China the rainfall increases in July. In August the precipitation reduces in the North but increases in the South. For the rainbelt, the precipitation decreases in the rainy season in South China, in the rainy season in the Yangtze and Huaihe Valleys or in the rainy season in North China and Northeast China.(5)In relation to the seasonal evolution, the massive urbanization in the eastern China will delay the onset of the summer monsoon for2pentad in the north part of the South China Sea, but postpone the withdrawal for2pentad, so the cycle of the summer monsoon don’t change over the northern part of South China Sea. But for other regions, the urbanization doesn’t affect the outbreak and the withdrawal of the summer monsoon and only affect its strength. The impacts of the large-scale urbanization differ from season.