国家重点基础研究发展计划2013CB430206,2012CB955304;国家自然科学基金41075008,40830957;中国博士后特别资助基金2013T60901;中国博士后基金20110490854;中国气象局干旱气象科研基金批准号:KYS2011BSKY01资助的课题.*Project supported by the National Basic Research Program of ChinaGrant .2013CB430206,2012CB955304;the National Natural Science Foundation of ChinaGrant .41075008,40830957;the Sepcial Postdoctoral Science Foundation of ChinaGrant 2013T60901;the Postdoc-toral Science Foundation of ChinaGrant 20110490854;the Postdoctoral Science Foundation of the Institute of Arid Meteorology of China Meteorological AdministrationGrant KYS2011BSKY01