中文摘要：

利用采自贺兰山北部3个采样点的油松树轮样本,建立了区域树轮宽度年表。相关分析发现,5—7月的帕尔默干旱指数（PDSI）与区域树轮宽度差值年表（RES）具有良好的相关性。因此,利用RES重建贺兰山北部1759—2005年来5—7月的PDSI变化,重建方程的方差解释量达47.90%,且方程稳定。贺兰山北部5—7月的PDSI重建序列平均值为-0.41。重建结果揭示了20世纪20年代干旱事件和19世纪后期、20世纪中期两个显著湿润期的存在。

英文摘要：

A drought index series reconstruction for north-central China was presented based on tree-ring-width chronologies developed from three sites of Pinus tabulaeformis in the northern Helan Mountains. The drought index reconstruction,spanning 1759-2005,was developed by calibrating the tree-ring-width chronologies with the Palmer drought severity index （PDSI）,which describes the regional moisture condition properly. The reconstructed PDSI in May-July （PDSI5-7） was verified with independent data,and accounted for 47.90% of the actual PDSI5-7 variance during their common period （1953-2005）. The mean of PDSI5-7 over 1759-2005 was estimated at -0.41. The full reconstruction indicates that the regional drought variability was relatively stable during the nineteenth century,but became more variable and persistent during the twentieth century. The drought epoch in the late 1920s was the severest one and the 1870s and 1940s were two wetter decades in our reconstruction.