树轮记录的川西高原北部过去325年7～8月平均气温变化

A 325-YEAR RECONSTRUCTION OF JULY-AUGUST MEAN TEMPERATURE IN THE NORTH OF WEST SICHUAN DERIVED FROM TREE-RING

利用采自川西高原北部地区的2个采样点的树轮样本,建立了该区域树轮宽度标准化年表.通过与气候要素的分析发现,该地区树木径向生长主要受到温度的限制,树轮年表与7～8月平均气温相关较好（r=0.74）.由此重建了川西高原北部地区325年以来的7～8月平均气温变化,重建方程稳定可靠,方差解释量为54.6％.重建结果显示,在过去的325年中（1686～ 2010年）,该地区先后经历了6个偏冷时段（1691～ 1704年、1768～ 1797年、1837～ 1852年、1888～1898年、1907～ 1932年和1963～ 1996年）和6个偏暖时段（1705～ 1767年、1798～ 1814年、1823～ 1836年、1853～1866年、1874～1887年和1950～1962年）,其中1705～1767年是持续时间最长的暖期,持续时间为63a,其年平均气温比多年平均气温偏高0.54℃;在偏冷时段中,1963～1996年是持续时间最长的冷期,持续时间为34a,其年平均气温比多年平均气温偏低0.48℃.通过时空相关性分析,表明重建序列具有较好的时空代表性.此外,重建结果与海螺沟冰川末端变化表现出很好的契合度,例如,20世纪初至30年代为冰川相对稳定或前进阶段,重建序列表现为一段偏冷期（1907～1932年）;与周边邻近地区研究结果对比分析中发现,重建结果与其他研究结果具有很好的一致性,例如,重建的长江源区玉树的夏季（6～8月）平均最低气温序列、重建的松潘地区年平均气温序列与重建序列较好的体现了20世纪80年代以来有一个显著的升温趋势、20世纪10～30年代的低温时期、20世纪50年代至60年代的高温时期、18世纪70年代至90年代的高温时期;气象灾害文献记录中的极端事件（如雪灾、冻害、干旱等）也能印证本文的重建结果,例如,20世纪60～90年代初,历史记录显示该区域是一个大范围的雪灾多发区,阿坝州境内的阿坝县、松潘县、若尔盖县等连续多年雪灾、霜冻,造成大量农作物减产甚至死亡,大量牲畜死亡,给农牧业带来严重损失.

It is important to develop new tree-ring chronologies in this region, in order to recognize climatic variation in the past on the north of west Sichuan. Fir （Abies faxoniana） tree-ring samples were collected from the north of West Sichuan. West Sichuan is located at the boundary between the Tibetan Plateau and the Sichuan Basin. Its climatic system is complicated because it is influenced by southeast monsoon, southwest monsoon, and the Tibetan Plateau. The two samples sites are Rejigou region （100°49＇N, 32°16＇E; 3680m a.s.l.） and Rewugou region （ 103°23′N, 32°17′E; 3530m a.s.l.）, which recollected from the north of Tibetan Qiang Autonomous Prefecture of Ngawa. Tree-ring samples were prepared, cross-dated and measured following conventional procedures. The calculation shows that the tree-ring width was significantly correlated with temperature, and the chronology had the highest correlation （r = 0.74） with mean temperature from July to August. Based on the analyses, we reconstructed July to August from 1686 to 2010. The reconstruction captures 54.6% of the instrumental temperature variance. In the past 325 years （ 1686 - 2010） , there were 6 cool periods （ 1691 - 1704, 1768 - 1797, 1837 - 1852, 1888- 1898, 1907 - 1932, and 1963 - 1996） and 6 warm periods （ 1705 - 1767, 1798 - 1814, 1823 - 1836, 1853-1866, 1874-1887, and 1950- 1962）. The longest warm period is 1705 - 1767 （63 years） , which annual mean temperature is 0.54℃ higher than average temperature and the longest cool period is 1963 - 1996 （34 years）, which annual mean temperature is 0.48℃ lower than average temperature. According to analysis of temporal and spatial correlation, it indicated that the reconstructed series with good temporal and spatial representation. Our reconstruction was validated by other temperature reconstructions from the surrounding area, e.g. the temperature reconstruction from June to August, the annual temperature reconstruction and our reconstruction shows that there is a significant warming trend since 1980s. Glacier advances, e.g. when the glacier is relatively stable or progressive stages form 1900s to 1930s, our reconstruction shows a cool period （ 1907- 1932） and retreats, e.g. retreats show that the region is a large range of snow disaster prone areas form 1960s to 1990s which caused serious losses to farmed livestock.