A multi-century spring precipitation history for northern Iran derived from tree-ring δ18O

Knowledge about the long-term hydroclimatic variability is essential to analyze the historic course and recent impact of climate change, especially in semi-arid and arid regions of the world. In this study, we present the first tree-ring δ¹⁸O chronology for the semi-arid parts of northern Iran based on juniper trees. We were able to reconstruct past hydroclimatic variability for the past 500 years. The highly significant correlation between tree-ring δ¹⁸O and spring precipitation indicates the primary influence of spring moisture availability on δ¹⁸O variations. The thereof derived precipitation reconstruction reveals short and long-term variability of precipitation intensity, duration, and frequency of dry/wet events. During the past 500 years, the driest period occurred in the 16^th century, whereas the 18th century was comparably wet. A gradual decline in the reconstructed spring precipitation is evident since the beginning of the 19th century, culminating in the continuing drought of the 20^th century. An analysis of dry/wet years indicated that over the last three centuries, the occurrence of years with a relatively dry spring is increasing. In contrast, more humid spring conditions are decreasing. However, the overall frequency of the occurrence of extreme events increased over the past five centuries. In addition, past hydrological disasters recorded in Persian history were well represented in our reconstruction. Correlations between our reconstructed precipitation record and large-scale circulation systems revealed no significant influence of large-scale climatic drivers on spring precipitation variations in north Iran, which therefore seem to be mostly controlled by a regional climate forcing.