贺兰山树轮晚材宽度记录中的降水量变化

THE PRECIPITATION RECORDS FROM TREE-RING LATEWOOD WIDTH IN THE HELAN MOUNTAIN

通过贺兰山地区树木年轮晚材宽度的研究,建立了贺兰山地区最近250年来的树轮晚材宽度年表。与气象观测记录的相关分析结果表明,树木生长与生长季当年5—7月降水量呈明显的正响应,在此年表的基础上重建了贺兰山地区过去250年来5—7月降水量,发现其具有明显的干湿变化,相对干旱年占总年数的52%,相对湿润年占总年数的35 5%,平年为14 5%,旱灾是该地区主要旱涝灾害。谱分析结果显示该地区5—7月降水有明显的2 6、3 5、21 3年的3个准周期。同时贺兰山地区降水量的变化历史可以反映东亚夏季风的变迁历史。

Tree ring width is an important proxy for the researches of past climatic changs. By measuring the ring width of Pinus tabulacformis, analyzing the relation between the width and climatic factors, precipitation was reconstructed in the area of the Helan Mountain(38°31′N,105°46′E), which is located in the west environmental sensitive zone in north China, or in the transition from arid to semiarid regions (monsoon to nonmonsoon). Precipitation is the main limited factor for tree growing in the area. We gave the correlation coefficient between ring latewood width and precipitation from May to July (r=-0678, p<001). Based on this, the precipitation from May to July was reconstructed by using the ring latewood width for the past 250 years. The explained variance of the reconstruction is 468%(R2). The result of the reconstruction shows that 18641878AD and 19721996AD were two dry periods in the area in the past 250 years. Also, 18291863AD,18791907AD,19541971AD were wet periods. The power spectrum analysis shows that the precipitation from May to July in the area has significant cycles of 26, 35 and 213 years. Summer precipitation is mainly affected by East Asian summer monsoon, so the reconstructed precipitation from May to July is related to historical changes of East Asian summer monsoon in the area.