RECONSTRUCTION-OF SIX REGIONAL DRY /WET SERIES AND THEIR ABRUPT CHANGES DURING THE LAST 1000 YEARS IN EAST CHINA
Zhang De' er; Liu Chuanzhi(National Climate Canter, Beijing 100081)Jiang Jianmin (Beijing Meteorological College,Beijing 100081)
The reconstruction of climatic series in length over one thousand years with annual resolution is an objective proposed by the IGBP-PAGES. In this paper, the reconstruction of 6 regional dry /wet grade series with one--year resolution for the last 1 033 years in East China and the variation feature of them, such as periodicity and abrupt change, are presented.The historical regionalization of dry /wet climate is obtained from a cluster analysis on the annual data of 1470 ~ 1992 at 120 stations in China. In this paper, only 6 regions (Ⅰ~Ⅵ)have been selected to reconstruct the dry. /wet grade series, they are: region Ⅰ: HeBei, Ⅱ: ShanXi, Ⅲ: down reach of the Yellow hiver, Ⅵ: HeNan,Ⅴ: Jiang-Huai, Ⅵ: Su-Hang.The dry /wet series for a region are expressed by five grades: very wet, wet,nomal, dry, very dry denoted by the numbers 1, 2, 3, 4 and 5, respectively. The grading is based on the descriptions in the historical documents. The reconstructed regional dry /wet series is from 960 to 1992 A. D., total of 1 033 years. In these series,there is data missing except series V. The number of absences for each regional series are as following, series Ⅰ 60, Ⅱ 140, Ⅲ 86, Ⅳ 37, Ⅴ 0, Ⅵ 15, respectively. The reliability of the regional series is checked by the statistic examine for each series and comparison with other proxy data.Spectral analysis shows that those periodicities presented in modern climatic analysis also existed in the last 1 000 years, such as the periods of around 3--year in all 6 regions, and those around 11 -year, 25 -year, 36-year even 80-year in some regions. This should be important to promote our knowleges on the variations in wetness.Abrupt change is a non-linear property of the climate system. It is defined as changes in the climate from a comparatively stable state toward suddenly another stable state in shorter period. In this study, we detect the signs of abrupt changes in the 6 regional dry /wet series by using moving t-test. An abrupt sign is identified in the statistic significance when the statistic "t" absolute value more than the criterion t0.01.It is indicated that during the last 1 033 years, abrupt climatic changes in wetness have occurred for many times in East China. The abrupt changes on century scale ob served in two or more regions in East China occurred around 1070, 1266, 1345, 1540,1690 and 1898 A. D., and those on 10 ~ 20 year scale occurred around 1217, 1266,1578, led, 1693, 1708 and 1899 A. D. in which the abrupt changes around 1578 and led have already been revealed by Yan. E(1993). The abrupt changes either on century scale or on decadal scale more frequently occurred in the northErn regions than that in southern ones.It is interesting that the abrupt changes (toward dry or toward wet), are almost consistent in the region Ⅰ - Ⅴ of the northern China but they do not always coincide with that in region Ⅵ located in South China. Besides, more abrupt signs are de tected in the 17th century, the coldest century of The Little Ice Age, but not any one in the 18th century, a moderate warm period. It seems that such abrupt events correspond to a cold climate background, although such sign is also detected in the warmest middle of the 13th century during the recent 1000 years and at the end of the 19th century, a rapidly warming times. It is noted that such abrupt changes on century scale have not yet occurred in the 20th century and that on 10 - 20 year scale have not also occurred in the recent 40 years. Therefore, it is worth to pay more attention to a potential reoccurrence of such abupt change in the future.