2000年来我国旱涝气候演化的阶段性和突变

THE MODES AND ABRUPT CHANGES OF CLIMATE IN CHINA DURING RECENT 2000 YEARS

过去气候的突变以地质方法得到很多证据，但在历史时期则发现不多。本文利用文献档案资料建成2000年来的旱涝气候序列，发现280年和1230年前后有过两次突变。本工作着重给出突变前后的旱涝气候分布类型的差别，即从空间分布上探讨被突变界开的气候阶段所具有的特色，280～1230年间，我国气候大趋势是不稳定的，而且涝的界线一再受到NE-SW走向的等高线阻挡。气候突变事件的证据说明，气候系统的运动具有两种模式：渐变和突变。

1 Introduction The past climate record clearly shows that the instrumental record contains only a subset of possible climate system behavior. TIs is highlighted by palaeoclimatic evidence that the climate system repeatedly switched, in a matter of years to decades, between significantly different climatic modes.The abrupt events, discovered within recent years, mainly occurred within glacial period or transition period from cold to warm, which were caused by the melting and freezing process of huge ice sheet, these processes drove the vertical oceanic circulation and result in the abrupt climatic changes.More recently, it has been found that abrupt climatic events also characterized the recent Holocene period, particularly at low--to mid--latitudes.The authors will examine abrupt events occurred within recent 2 000 years, and map out the special temporal patterns of change associated with past abrupt events,which will be helpful for discussing the causes and for predicting these abrupt events.2 Data sourcesIt was a rule in China for the new dynasty to compile the history of the previous dynasty. Documents, archives, and books from the last dynasty were the main sources for compilation. There are twenty five editions of official histories currently exist.Archives of the Qing dynasty is a main source to reconstruct past climate of China. About 10 million volumes of archives, which include archives of the file--store in the Cabinet, Military Administration and Official Histories, Archives of the Palace, various governmental departments outside the Palace and some personal possessions, are kept in No.l History Archives.In ancient China, all government decisions, no matter important or not, were made by the emperors, thus a good reporting system was needed for the emperors to operate and run the governments' As a result, reports to emperors constitute an important part of the Qing archives.The fourth source of the data was local gazettes including local political, economic,culture and natural histories' They are abundant and cover wide area of China. In addition, archives of 19if ~ 1949 A. D. and newspapers from 1930 ~ 1936 A. D. are also investigated.Using the above data we categorized 5 climatic indexes: severe drought, drought,flood and heavy flood, and in addition, the good harvest.Their occurrence, frequency mode (the most frequent grade within a certain period) and other index were adopted for the statistics and, ultimately were used to explain the climate.Because some data can be only found in a specific region, thus in this paper we will focus on studying the region of 25 ~ 40 °N, 105 ~ 120° E for the whole 2 000years, and all the original data of Fu (covering 3 ~ 10 counties) were clustered into 40 spots in this area.3 Abrupt climatic change during recent 2 000 years This paper adopted a frequency variance--analysis method to detect the abrupt event within the 2 000 years in stead of the Mann-Kendall test, because the authors thought the climate data is random in distribution. Based on the test, two main abrupt changes, 280 A. D. and 1230 A. D. were identified, which divided the 2 000 years climate into three episodes. The climate before 280 A. D. was wet and stable, between 280A. D. and 1230A. D. was unstable, and after 1230 the climate became stable again and drier than before. The present climate dry-regime in the north and west;wet in the south and east was set up since 1230 A. D.There is a consistent tendency of drying for the last 2 000 years. The most humid climate occurred before 280, severe drought occurred between 280 ~ 500 A. D., and after 1230 A. D. there is a stable and dry regime.The abrupt events were also demonstrated by the following analysis: Lake sediment in Kunminghu of Beijing (a hiatus occurred in the 11th century).The Guliya ice core in Qinghai -Xizang (Tibet) Plateau (an abrupt change at 1100A. D.). And salt-lake sediment in inner Mongolia also prove this result also.4 Spatial patterns associated with the abrupt changes The spatial patterns of drought /flood frequencies isolines were drown