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Study on Dry and Wet Climatic Changes of Eastern and Mid-China Region in Recent 510 Years

SONG Bao-ping~(1,3),WANG Zhang-hua~2,LE Qun~2,KOU Ying~3,FU Yun-fang~4 (1.Department of Resources & Environment,Shijiazhuang College,Shijiazhuang 050035; China Normal University,Shanghai 200062; 3.Department of Geography,East China Normal University,Shanghai 200062; 4.Department of Computer,Shijiazhuang College,Shijiazhuang 050035,China)  
Historic records are considered as important data sources in climatic change study.To reveal evolution rules and trends of dry and wet climate in Eastern and Mid-China area,four places (Shanghai,Wuhan,Tianjin and Xi'an) are selected,all of which locate in the East-Asia monsoon controlling scope.The data of drought and waterlogging grades,from 1470 to 1979 in four places,are used to establish dry/wet series,which are calculated using method of Mexican Hat wavelet transformation.Then multi-time scale wavelet transformation graphs and abrupt change points of dry-wet climate of each place in the recent 510 years are obtained.The analyzing results show that the dry and wet phases in 270 a and 135 a time scale are similar between Shanghai and Tianjin(in East China) or Xi'an and Wuhan(in Mid-China).For 70 a and 30 a time scale,there are more frequent fluctuations of dry and wet climate in Xi'an than in other regions.Dry and wet climatic changes respond obviously to the Little Ice age of the 17~(th) century and comparatively stable age of the 18~(th) century in East China,but tardily or unsteadily in Mid-China.However,climate of each region is changing to dry after the 20~(th)century,which relates with possibly the warming occurrence in the early part of the 20~(th) century.As a whole,dry and wet climate changes in Eastern and Mid-China area display some East-west differences before 18~(th)century,and are trending towards coherence. Effect elements of dry and wet climate changes are discussed too.Transformation of atmosphere circulation systems due to non-local climatic changes and relative sea-land position control the dry-wet changes in long time scale.The differences of physical local environment and human activity are the effect elements to climate change in short time scale,and are only some interferential element to climatic evolution trends.
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