气候变化领域集成服务门户

A millennium-long tree-ring width chronology for the middle Qilian Mountains in northwestern China has been developed back to A.D. 775. Correlation analysis indicates that the tree-ring width reflects growing-season moisture variability. Our chronology reveals three distinct periods based on the prevailing moisture anomalies: A.D. 775-1101 (wetness persistence), 1101-1831 (dryness persistence) and 1831-2006 (wetness persistence). A 31-year running mean through the tree-ring index series clearly shows seven obvious dry spells and eight wet spells. Compared with the proxies associated with the East Asian monsoon and the westerlies in the past millennium, our moisture-sensitive tree-ring chronology revealed that the East Asian summer monsoon had a strong influence on tree growth before A.D. 1300. From about A.D. 1450-1750, the westerlies strongly affected the Qilian Mountains. After A.D. 1750, a combined influence of both East Asian monsoon and westerlies was apparent. In the past century, the effect of westerlies has become stronger. Our results suggest that tree rings can preserve the information on the advance and retreats of the westerlies and the East Asian summer monsoon. Additionally, this research is helpful for understanding the driving mechanism of the Asian monsoon and the westerlies in northwestern China over the past thousand years.