祁连山中部公元904年以来树木年轮记录的旱涝变化

利用取自祁连山中部地区的树木年轮样本和该地区3个站点的降水资料,应用年轮气候学方法,重建了祁连山中部地区的降水量.自公元904年以来,该地区历经了31次相对干期和30次相对湿润期,其中,连续两个10a以上的干期有17次,湿润期12次,最长的干期是1540—1590年间,长达60a,最长的湿润期是1240—1270年、1860—1890年,各有40a.世纪尺度范围内,16世纪是最干的100a,有80a为少雨年;最湿润的是13世纪和19世纪,这期间有60a为多雨.自公元904年以来,降水量共发生了35次突变,16次是由旱向涝的突变,19次是由涝向旱的突变.平均约30a发生一次.11世纪是该地区降水的多变时期,15～16世纪是降水的相对稳定时段,20世纪又进入了降水的多变时期.

A Record of Drought and Flood Series by Tree-Ring Data in the Middle Section of Qilian Mountain Since 904 A.D.

The standardized (STD) chronology was established from tree\|ring data of Sabina Przewalskii in the middle part of the Qilian Mountains. The correlation was analyzed between the tree\|ring index and the precipitation in weather stations, near which the tree ring is sampled. The results showed that there were 31 dry spells and 30 wet spells in the past \{1 100\} years, of which 1540\_1590 A.D. was the longest dry period, lasting 6o years, and 1240\_1270 A.D. and 1860\_1890 A.D. were the longest wet periods, lasting 40 years respectively. There were 17 durations of dry period over 10 years, and 12 durations of wet period over 10 years. With regard to the century time scale, the 16th Century was 100 years of drought, with 80 years being lack of rain. The 13th Century, as well as the 19th Century, was 100 years of wet, with 60 years in spate. At the same time, another characteristic of precipitation variation in these mountains is more abrupt change. There have had 35 abrupt changes since 904 A.D., about 30 years on the average. There were 16 shifts from drought to wet, and 19 shifts from wet to drought. There were 9 abrupt changes in the 11th Century, 2 abrupt changes in the 15th and 16th Centuries. In the 20th Century there were 3 abrupt changes. Precipitation in these mountains frequently changed in the 11th Century, and less changed in the 15th and 16th Centuries. In the 20th Century precipitation changed frequently.