中文摘要：

植被覆盖的变化是气候变化的成因之一,植被改变对气候的反馈可能会加强或者减缓气候的变化。文中利用CCM3全球气候模式以及20世纪70年代和90年代中国西部的植被覆盖资料进行数值模拟试验,研究了这两个时期植被变化对北方夏季区域气候的影响。模拟结果表明：植被增加的地方,地面吸收的辐射通量增加;植被减少的地方,地面吸收的辐射通量减少。地面辐射平衡的变化造成局地大气热量异常,并引起周边大气热量的调整,从而导致东亚地区夏季大气环流异常。相对于70年代的植被状况,用90年代植被模拟的北方地区对流层上层为异常气旋性环流,而中、低层为异常反气旋环流,东北亚到中国东部盛行异常北风,同时西太平洋副热带高压强度偏弱、位置偏南。这种异常环流特征说明模拟的90年代中国东部夏季风明显减弱,异常的环流形势造成华北和东北地区夏季水汽输送减少,水汽辐合减弱,年降水量减少了40 mm,呈现减少的特征,这是和观测事实是比较吻合的。降水和环流的异常还造成华北和东北夏季平均地面气温降低了0.4—0.8℃。因此近30年来中国西部植被变化可能是东亚夏季风年代际变化以及北方夏季降水减少的一个重要因素。

英文摘要：

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.