关键词: 文献记载, 旱涝序列, 树轮干湿, NAO

Abstract: Plenty of historical documents was used in this paper to reconstruct the droughts and floods sequence of Hexi region during AD 1436-1946, which is usually called the Little Ice Age (LIA). The climatic related records of this region were collected and classified into 5 levels year by year using traditional classification methods, from 1 to 5, each was defined as wet (humid), mildly wet (humid), normal, mildly dry and dry, respectively. The series of dry and wet levels comprises the annual drought/flood (D/F) sequence and tenyear mean value of D/F sequence, both of which highly reflect the precipitation variation. It is revealed that during the following periods, there happened much more drought events, such as, AD 1460-1539, AD 1616-1665 and AD 1907-1949, while droughts happened during the third and fourth ten years of the 20th century were the most severe ones. Flood events were more often during AD 1725-1748 and AD 1879-1906. Compared with the treering data of the Qilian Mountains nearby, the result indicates that both of them are highly consistent. Flood events correlate to relatively high treering index, while drought events have a good respond to low treering index, which makes the reconstruction of the D/F variation for Hexi region reliable. Added with the North Atlantic Oscillation (NAO) index, it turned out that during the relatively cool period of LIA, NAO played the leading role in precipitation of Hexi region with the high NAO index going along with drought events while low one going with flood events, while during the relatively warm period, both NAO and the force of the Asian Monsoon determine the precipitation of Hexi region.

Key words: document record, D/F sequence, dry and humid, NAO