以树轮宽度重建九寨沟1750年以来冬半年平均最低温度

WINTER MEAN LOWEST TEMPERATURE DERIVED FROM TREE-RING WIDTH IN JIUZHAIGOU REGION,CHINA SINCE 1750A.D.

利用四川九寨沟地区树轮宽度年表对该地区1750A·D.以来的冬半年(上年11月到当年3月)平均最低温度进行模拟重建,重建方程的方差解释量为46·2%(调整自由度后为45·1%)。结果表明,九寨沟地区在重建期间平均最低温度较低的时段主要有1814～1844年和1937～1984年两个阶段;而平均最低温度较高的时段主要有1795～1813年和1984年至今两个时期,其中1984年之后的升温时段尤为显著,与川西其他地点冬季温度重建非常相近。计算显示,与尼泊尔Kathmandu冬半年平均气温(上年10月到当年2月)相比,九寨沟地区冬半年平均最低温度存在显著2年滞后(r=0·27,p<0·0001),而1825年前后及1970年前后两个冬季低温时段在两个地点大体是一致的,这些现象表明青藏高原周边地区冬半年温度变化的趋同性。功率谱分析表明,九寨沟地区冬半年平均最低温度2·11～6·86a的准周期与ENSO周期比较一致,而18·46a准周期则显示了该地气温变动与天文准19a周期有一定关系。

So far there is a few dendroclimatogical studies being carried out in the Jiuzhaigou region, China. Most treering 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） treering 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 treering 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.