Relative humidity is an important factor in water and water vapor feedback cycles.In this study,we established a 222-year annual tree-ring δ^(18)O chronology for Siberian larch(Larix sibirica Ldb.)from the Altay Mountains in northwestern China.Climate response analyses revealed that the relative humidity was the primary factor limiting tree-ring δ^(18)O fractionation.Based on our analysis,tree-ring δ^(18)O can be used to reconstruct the July–August relative humidity based on both a reasonable mechanism of tree-ring δ^(18)O fractionation and a statistically significant regression model.We used this model to reconstruct variations in the July–August relative humidity,and the model explained 47.4% of the total variation in the measured relative humidity data from 1961 to 2011.The relative humidity in the study area increased from 1900 to the 1990s and decreased thereafter.Two regime-shift dry periods were detected during the study period(one from 1817 to 1830 and the other from 2004 to 2011).
High-resolution tree-ring δ18O chronologies covering the last millennium,although scarce,are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau.For this study,a tree-ring δ18O chronology with a temporal resolution of 3-years was developed from the long-lived Qilian juniper(Sabina przewalskii Kom.),extending back in time to AD 991.This long δ18O chronology was significantly correlated with the yearly δ18O in tree rings during the common period from 1800 to 2006,and was an effective proxy for relative humidity during the growing season.A low-frequency moisture pattern signified the occurrence of a slight drought during the Medieval Climate Anomaly,a marked occurrence of a wet period during the Little Ice Age,and a trend in increasing moisture levels,although lower than average,alongside the Twentieth Century warming trend.Comparisons to other hydroclimatic reconstructions indicate that this tree-ring18O chronology serves as a reliable paleo-humidity proxy for the Qaidam Basin as well as documenting details of past humidity levels in the region.
WANG WenZhiLIU XiaoHongXU GuoBaoSHAO XueMeiQIN DaHeSUN WeiZhenAN WenLingZENG XiaoMin
