Spatial patterns of change trend in rainfall of China and the role of East Asia summer monsoon

On the basis of NCEP/NCAR Reanalysis 2.5°×2.5° monthly mean sea level pressure data and monthly rainfall data of 579 stations in China from National Climate Centre for period from 1961 to 2007,the spatial patterns of change trend in rainfall of China,and the relationships between East Asia summer monsoon and rainfall of China in summer and autumn are investigated by use of trend coefficient,relative variability and irregular domain gridding.Irregular domain gridding method means data is processed by China map boundary file after it is gridded by Kriging to rectangle domain including whole China domain.Results show that Northeast China,North China,eastern part of Northwest China,eastern part of Southwest China,and western part of South China,which form a northeast-southwest belt,present a falling trend,while western and southern part of China present a increasing trend.The falling trend over northern part of Shannxi and the increasing trend over northwest part of Xinjiang are significant.The report of rainfall falling trend in western part of South China,mainly in Guizhou,Guangdong and Hainan province,has no seen in previous literatures,this is a new drought tendency that we must pay attention to.In winter,increasingly tendency appear over most parts of China,only a few parts show falling trend,for example,North China and Southwest China;in spring,eastern area of Qinghai-Tibetan Plateau present a significant increasing trend while southern part of Shannxi present a significant falling tendency;in summer,falling trend can be seen over Northeast China,North China and Southwest China,while rainfall over Southeast China and Northwest China are increasing,and significant level is reached over northern part of Xinjiang and of Qinghai;in autumn,falling trend appears over East China,while increasing trend appears over western area and significant level of falling are reached over southern part of Gansu and eastern area of Sichuan.The rainfall area with increasing trend is greater than that with falling trend from 1961 to 2007;similarly,the rainfall area with increasing trend is greater than that with falling trend in winter,spring and summer,only the area percentage is reverse in autumn.The area of lowest relatively variability is distributed over Southwest China and South China,while the area of highest relatively variability is distributed over southern part of Xinjiang and western part of Inner Mongolia,which all is desert belt included Taklimakan Desert and Badain Jaran Desert;the seasonal distribution is similar;this is a meaningful discovery that highest rainfall relatively variability area is exactly fitted with famous desert belt,we can make use of rainfall relatively variability to predict future potential desert areas,and it is helpful to deal with desertification problem in China,even world.Two significant falling process of East Asia summer monsoon intensity can be seen in the last 61 years,which is in the middle of 1960s and 1970s.The relationships is significant between East Asia summer monsoon and rainfall of China in summer and autumn.The weakening of East Asia summer monsoon intensity may have a significant role in the process of rainfall falled in the regions of Northeast China,North China and Southwest China in summer,as well as East China in autumn.