树轮记录的黄河源区1505～2013年5～9月相对湿度变化

TREE-RING BASED MAY-SEPTEMBER RELATIVE HUMIDITY RECONSTRUCTION DURING 1505~2013 IN THE YELLOW RIVER SOURCE REGION

根据采集自青海省玛沁县雪山乡的祁连圆柏建立树轮宽度年表。通过相关分析发现，树轮宽度标准化年表（STD）与黄河源区内4个气象站平均5～9月相对湿度存在显著的正相关关系，相关系数达到0.60（建模期为1969～2013年）。利用标准化年表重建了黄河源区过去509年的5～9月平均相对湿度变化序列，重建方程方差解释量达36.0%，且方程稳定可靠。重建序列在过去509年先后经历了6个湿润阶段和8个干旱阶段：湿润阶段为1655～1697年、1746～1793年、1795～1816年、1898～1916年、1933～1957年和1962～1992年；干旱阶段为1530～1541年、1544～1586年、1590～1634年、1728～1745年、1817～1836年、1856～1886年、1917～1932年和1993～2004年。利用多窗谱分析（MTM）表明，重建序列具有85～256a、3.0～3.6a和2.0～2.8a左右的显著周期变化。通过对比发现，此次重建序列与黄河源区附近及青藏高原东北部其他一些能反映干湿状况的树轮重建序列在低频上具有较好的一致性。

The source region of the Yellow River is in the northeastern area of Tibetan Plateau（32°30＇～36°12＇N, 95°50＇～103°30＇E）. This area is arid with a plateau-continental climate, which is in drought throughout the year. Its climate is affected by the plateau monsoon. This important region of the Tibetan Plateau has experienced changes in geographic environment and climatic conditions. These changes play a significant role in the Tibetan Plateau climate change, and will lead to problems in the social and economic development of Northwest and North China. It is important to develop new tree-ring chronologies in this region, in order to recognize climatic variation in the past. Tree-ring width chronology was created by Sabina przewalskii Kom. which collected in Xueshan Township of Maqên County of Qinghai Province（XS：34°77.293＇N, 99°67.817＇E; 3780～3811m）. In total, 51 cores/26 trees were collected. All samples were surfaced, cross-dated and measured according to standard dendrochronology techniques. Three types of tree-ring width index chronologies were created：Standard （STD）, Residual （RES） and ARSTAN （ARS） chronologies. The STD chronology, which preserves more growth features, was applied in this study. Correlation analysis indicates that there is significantly positive correlation between tree-ring width standardized chronology（STD）and the average relative humidity of four meteorological stations（May-September）in the source region of Yellow River（r=0.61969～2013）. Based on the analyses, the relative humidity sequence in May-September of Yellow River source region during 1505～2013 was reconstructed. The reconstructed equation was stable and reliable and its explain variance reached 36.0%. In the past 509 years, there were 6 wet periods（1655～16971746～17931795～18161898～19161933～1957 and 1962～1992）and 8 dry periods（1530～15411544～15861590～16341728～17451817～18361856～18861917～1932 and 1993～2004）. The longest wet period is 1746～1793（48 years）, and the longest dry period is 1590～1634（44 years）. The wettest period is 1970s～1980s, and the driest period is 1600s～1620s. There were 18 extremely dry years：1510, 1513, 1536, 1605, 1606, 1607, 1608, 1609, 1617, 1618, 1626, 1627, 1824, 1831, 1871, 1895, 1927 and 1998; and 4 extremely wet years：1773,1910,1975 and 1986. Comparison with the dry/wet events recorded in the history of the region from the yearly charts of dryness/wetness in northwest China for the last 500-year period shows many extreme years（wet years such as 1773 and 1986）and dry years（1510 and 1927）in the reconstruction. The multi-taper method（MTM）spectral analysis indicates that there are 3 periodic change of 85～256a, 3.0～3.6a and 2.0～2.8a. The 3.0～3.6a and 2.0～2.8a cycles may relate to the Quasi-biennial and Southern Oscillations influenced by alternating east-and west-wind regimes in the equatorial stratosphere lasting 26～30 months. By comparing the reconstructed sequence with the two reconstructed series which can reflect the status of dry and wet in the source region of Yangtze River and the northeastern Tibetan Plateau, it is found that these three areas share the same drought（1810s～1830s, 1870s～1880s and 1920s～1930s）and wet periods（1750s～1760s, 1890s～1910s, 1940s～1950s and 1970s～1990s）on an inter-annual scale. The result shows that these series have good consistency change on the low frequency. Compared with other tree-ring chronologies of nearby areas, we found that some dry periods, such as 1728～17451817～18361856～1886 and 1917～1932, coincide with low-growth periods of trees in these regions. Furthermore, we explore the climate mechanisms between the reconstruction and large-scale climate forcing.