树轮宽度记录的天山东段近200 a干湿变化

利用采自天山东部两处不同地点上下限的西伯利亚落叶松(Larixsibirica Ledb.)树轮样芯,分别建立了树轮宽度年表.经相关普查和响应函数的计算表明,天山东段森林下限的树轮年表与该地区3~6月的降水和气温相关显著,通过定义湿润指数,以树轮宽度为指标,重建了天山东段巴里坤地区近200 a来春季至初夏湿润指数的演变历史,解释方差为42%.统计分析表明,重建的湿润指数序列与邻近气象站的器测资料计算得到的湿润指数序列呈显著的正相关关系.重建序列能较好地反映天山东段近200 a来春季至初夏的干湿变化,在200 a中有6个显著的湿润时段和7个显著的干旱时段.天山东段近200 a来3~6月湿润指数序列的显著周期是11 a,然后依次存在16 a、5 a、8 a、3 a和32 a的稳定周期.

Variation of the Dryness in the Recent 200 a Derived from Tree-Rings Width Records in the East Tianshan Mountains

Tree ring width chronologies are constructed by using the tree ring cores of Larix sibirica Ledb.from four sites in eastern Tianshan Mountains.Correlation census and response functions show that the tree ring index closely relates to both precipitation and temperature in March-June(spring to early summer) at forest lower limit.The moisture index(P/T) during spring to early summer is reconstructed by using tree ring width at Barkol area in East Tianshan Mountains in the recent 200 years,with an explanation variance of 42%.Many statistical methods,such as sign test,one order difference sign test and error test,have shown that the reconstructed equation of the moisture index is reliable.It is found that the significant positive correlation between the reconstructed moisture index and the moisture index calculated from the observed data of the nearest meteorological stations,with a coefficient of 0.648.According to the definition of the moisture index,the change of the reconstructed moisture index sequence can be used to describe the change of dryness in the East Tianshan Mountains in the recent 200 years.In this area,there are 6 and 7 remarkable moist and dry periods,respectively.The reconstructed moisture index from March to June in the recent 200 years has stable periods of 11,16,5,8,3 and 32 a.