Characteristics of extreme droughts inferred from tree-ring data in the Qilian Mountains, 1700-2005

摘要

Severe droughts were evaluated using a tree-ring network of 12 chronologies(1700-2005) from the Qilian Mountains on the northeastern Tibetan Plateau. A total of 98 droughtyears, including 78 moderate, 15 severe, and 5 extreme events, were identified for the past 306 yr.Following the starting year of a drought phase, drought commonly continued for 1 to 2 yr. The spa-tial patterns of moisture conditions in central and eastern China corresponding to 19 majordrought years during the period 1700-2000 were grouped into 3 clusters, with one particular pat-tern showing droughts of nation-wide impact (i.e. 1721,1928 and 1966). Drought events becamemore frequent during the 20th century. Moreover, the multi-year event during the late 1920s andearly 1930s was the longest in the past 306 yr. As shown by the tree-ring data, this extremedrought event occurred first in the western Qilian Mountains, and then progressed graduallytoward the central and eastern parts of the area, culminating in 1928. Comparison with historicaldocuments demonstrates that the climatic information imbedded in the tree-ring network canprovide quantitative measures of drought severity and fill the gaps where historical documentsare lacking and/or incomplete.