Reconstruction of precipitation using the chronology of juniper trees (Juniperus polycarpus) in North Khorasan Province, Iran

One of the most important challenges of climate studies in Iran is the lack of access to long-term climate data. Tree climatology, by examining the effects of climate on the annual rings of trees, provides the possibility of reconstructing the temperature and precipitation of past periods. The main goal of this study is to reconstruct precipitation from the width of annual circles of juniper trees (Juniperus polycarpus K.Koch) in the Garkhod region, located in the northwest of Khorasan province in Iran. The samples were prepared from the juniper trees with a chronometer drill and after initial preparation, they were read by LINTAB device and their time agreement was checked with TSAPWIN software. The final chronology was prepared using ARSTAN software and based on reconstructing the precipitation in the period 1850-2020. The results showed that the widths of juniper annual circles were not affected by temperature fluctuations. Still, the total precipitation of January-May showed the maximum positive and significant correlation coefficient with the growth of these trees. Between the months of the year, February, March, April, and May had the most positive and significant correlation with the width of the annual circles. In general, during the period of 1850-2020, 8 years except for positive symbolic years and 9 years were reconstructed as negative years. The highest precipitation occurred in 1864 and the lowest in 1917. It can be said that the precipitation influences the growth of juniper trees in the region. In this way, suitable conditions for the activity of cambiums are provided with the increase in precipitation.