Precipitation variations in the central Zagros Mountains (Iran) since A.D. 1840 based on oak tree rings

We established three tree-ring width chronologies from oak species in the central Zagros Mountains, Iran, where instrumental climate data only cover a short period (1951-2010). Due to high similarity of the individual ring-width series, we included all studied sites in a regional chronology covering 306 years. Correlation functions with regional climate data revealed significant positive correlations (p < 0.01) with total precipitation from previous October to current May. Thus, we reconstructed regional precipitation variability over the period 1840-2010 based on linear regression between regional tree growth and climate data. Dry conditions prevailed in the 1840s, 1850, 1870s, 1880s, 1900s, 1920s, 1940s, 1960s, 1980s and 1999-2003. In comparison to wet periods, the number and the intensity of dry periods have increased during the 1840-2010 study period. Many of the reconstructed wet years coincided with major El Niño events. Inverse association between the Southern Oscillation Index (SOI) and the reconstructed precipitation during the common period (1877-2010) revealed that the Southern Oscillation Index (SOI) plays an important role in regional precipitation variability.