Numerical simulation of the impact of changes in the vegetation in the western China on the summer climate over the northern China

The vegetation change is one of the main factors causing climate change, and its feedback to climate change may strengthen or mitigate the latter. Using the NCAR Community Climate Model (CCM3) and the vegetation distribution data of the western China in the 1970s and the 1990s, we have simulated the impact of vegetation cover changes in the western China on the summer climate over the northern China during the last 30 years. The simulation results indicated that the radiative flux absorbed at the surface was increased where vegetation flourished, while decreased in the area retrogressed. As a result, changes in the surface radiation balance caused local surface heat anomalies and the heat adjustment in the surroundings, leading to summer atmospheric circulation anomalies in the East Asian region. The numerical experiments with a difference in the type of vegetation cover in the western China set between the 1990s and 1970s forced an anomalous anticyclonic circulation center in the mid-lower levels in the north side of the Qingzang Plateau, and an anomalous cyclonic circulation in the eastern side of the Plateau at 200 hPa, accompanied by the prevalence of the anomalous northerly winds from the Northeast Asia to the eastern China at 850 hPa. Accordingly, the summer rainfall in the northern and northeastern China is decreased by about 40 mm in the 1990s relative to that in the 1970s. Moreover, changes in the vegetation cover also caused a decrease of summer air temperature by about 0.4-0.8 ℃ over the northern and northeastern China. Therefore, it follows that vegetation changes over the western China is also an important factor for the interdecadal variations in the East Asia summer monsoon and the decrease of summer precipitation in the northern China during the last 30 years.