WINTER MEAN LOWEST TEMPERATURE DERIVED FROM TREE-RING WIDTH IN JIUZHAIGOU REGION, CHINA SINCE 1750A.D.
以树轮宽度重建九寨沟1750年以来 冬半年平均最低温度*

So far there is a few dendroclimatogical studies being carried out in the Jiuzhaigou region, China. Most tree-ring studies were carried out in environmentally sensitive regions of China and focused on the reconstruction of rainfall. However, it is important to develop new tree-ring chronologies in this region, in order to recognize climatic variation in the past on the east margin of the Tibetan Plateau. In the summer of 2005, fir (Abies chensiensis) tree-ring samples were collected from Jiuzhaigou region (33°03'59.8″N,103°51'34.9″E). Jiuzhaigou is located at the boundary between the Tibetan Plateau and the Sichuan Basin. Its climatic system is complicated because it is influenced by Eastern Asian monsoon, southwest monsoon, and the Tibetan Plateau.Tree-ring samples were prepared, cross-dated and measured following conventional procedures. The calculation shows that the tree-ring width standard (STD) chronology is significantly correlated with the mean lowest temperature from the prior November to current March (r=0.679, p<0.0001, N=52). In this paper tree-ring data from Jiuzhaigou have been used to reconstruct the winter (from the prior November to current March) mean lowest temperature of this region since 1750A.D.Two cold periods, 1814~1844 and 1937~1984, and two warm periods, 1795~1813 and 1984 till now were recognized. The warm period since 1984 is the most obvious. The winter mean lowest temperature from 1844 to 1937 fluctuated smoothly. We compared the winter mean lowest temperature from Jiuzhaigou region with the mean temperature from the prior October to current February of Kathmandu, Nepal as well as the winter mean lowest temperature from other sites of the west Sichuan. The results show that the cold periods 1814~1844 and 1937~1984 in Jiuzhaigou region correspond well with those of other sites. It also indicates that the Tibetan Plateau affect the winter temperature synchronously in the surrounding regions. The Tibetan Plateau plays an important role in the variation of the lowest winter temperature in Jiuzhaigou region. Power spectrum analysis shows that there exist periods of 18.46, 8.89, 6.86, 6.67, 2.86, 2.73, 2.24, 2.22, and 2.11-year quasi-cycles in winter lowest temperature. The periods of 2.11 to 6.86 years probably are related to ENSO events, and the cycle of 18.46 years responds to a 19 years of astronomical period.