Relative humidity reconstruction for northwestern China's Altay Mountains using tree-ring δ18O

Relative humidity is an important factor in water and water vapor feedback cycles. In this study, we established a 222-year annual tree-ring delta O-18 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 delta O-18 fractionation. Based on our analysis, tree-ring delta O-18 can be used to reconstruct the July-August relative humidity based on both a reasonable mechanism of tree-ring delta O-18 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).