Reconstruction of paleo precipitation using Juniperus species dendroclimatology in Kerman region

Paleoclimatology studies attempt to detect climate change over time and fill meteorological data gaps in a variety of ways. One of the most widely used methods in Paleoclimatology and the reconstruction of climate data for decades and centuries is the use of tree rings. Trees, by forming annual growth rings, store past climate information, and dendroclimatological studies reveal this valuable information to us. One of the suitable species for these studies is the Juniperus tree, of which there are significant habitats in the study area - northern elevation of Kerman province. Considering the simultaneous effect of short-term and long-term water sources on annual tree growth, the aim of this study is to investigate the effect of different water sources on tree growth in the study region and then reconstruct rainfall conditions using annual growth rings of Juniperus trees in the habitat that is called "Tangal Ravar" in the north of Kerman province.

 "Tangal Ravar" Juniperus habitat is located in the northern highlands of Kerman province, at the 31°25' of North and 56° 50' of East. The highest peak of this mountain is 3515 meters above sea level, Juniperus trees in these heights are mostly distributed on the southern, southwestern and western slopes from 2700 to 3100 meters. Examination the data of climatic stations close to this habitat showed that the annual rainfall is about 200 mm and the average temperature is 20 degrees, which emphasizes the location of the habitat in semi-arid regions. The Precipitation regime in habitat is at cold season from November to April, and the habitat growing season lasts from about mid-March to late September.Sampling was performed in spring 2018. For this purpose, an increment borer with a diameter of 5.5 mm for hardwood was used. About 200 samples were taken from 96 trees that were as healthy and undamaged as possible. The rings were counted and their width was measured with LINTAB desktop and TSAPWin software with an accuracy of 0.01 mm. The cross dating between the growth curves of the trees was done with TSAP software and the results of GLK, CDI, GSL, CC and Tv statistics showed the desired quality of the that for most of the trees. Chronologies were created in ARSTAN software by BiweightRobust averaging method, and then de trending and standardized by negative exponential curve method and 20-year spline, and finally STANDARD chronology was selected for studies. The quality of chronology was measured by the mean correlation statistics of all habitat trees (Rbt), Expressed population signal (EPS), signal-to-error or anomaly ratio (SNR), mean sensitivity (MS), and Autocorrelation (AC1). Then, the relationship between climate and ring width was measured using station data from Kerman province and CRU TS4.01 climate data for the last 116 years in Iran by Pearson correlation coefficient and precipitation reconstruction was performed using simple linear regression.

  The quality studies of chronologies results showed that the longest chronologies prepared are 680 years (1338-2017 AD) with a confidence reconstruction period of 252 years and the chronologies have desirable values of quality measurement statistics. The average chronology of the region shows a relative decrease in the width of growth rings in the last two decades with a decreasing trend in the last century along with increasing fluctuations in the 1950s and 1980s. In general, we can see a decreasing trend in the width of the rings from 1500 to 1650 AD, an increasing trend from 1650 to 1750 AD, a decreasing trend from 1750 to 1800 AD, an increasing trend from 1800 to 1900 AD with an obvious decline in the 1850s and the trend Observed a decline from 1900 to the present. The study of the correlation between rainfall and the width of growth rings of juniper trees in "Tangal Ravar" habitat, which is a mountainous region with semi-arid climate, showed that rainfall before the growing season and the beginning of the growing season, or in other words, total annual rainfall is the most important and effective factor in the width of the rings. Also, the total rainfall of the coldest months (November, December and January) shows a high correlation with the width of the rings. The results of rainfall reconstruction also showed several droughts and wetlands along with fluctuations in ring width.

The results showed that precipitation in general has a direct relationship with the width of the growth rings of juniper trees in the region. Meanwhile, December-January precipitation due to snowfall and total precipitation of the rainy season, ie October-May, shows a high correlation with the width of the rings. Due to the high slope in the topography of the habitat, the rocky location of most trees, shallow soil and consequently low groundwater storage, juniper trees of "Tangal Ravar" habitat depend on the amount of rainfall before the growing season and the beginning of the growing season in the region. Due to the mountainous nature, most of the winter precipitation in the region is snow. Considering the high positive correlation between December-January and for some stations December-January-February, it can be said that snow storage before the start of the growing season plays an important role in the width of the growing rings of all habitat trees. Considering the reconstructed precipitation, the significant periods of drought and wet years in the region can be summarized as follows: Droughts of the last two decades, especially from 2007-2006 to 2017. Drought of 1980s, Drought of 1965-1975. Wet period of the 1950s, droughts of the 1940s, droughts of 1916-1919, wet period of the second half of the nineteenth century with a severe drought in the 1870s, a decrease in precipitation over a century from 1850 to 1750 with multiple droughts, increased precipitation in the period 1750-1700 AD with continuous wetlands. An obvious and continuous decline for 170 years from 1700 to 1520 AD. Among these, the important droughts of 1916-1919 and 1870-1871, which were accompanied by severe famines in Iran, have been mentioned in the results of other researchers.