Characteristics of Climate Variation Recorded in Tree Data During the Past 1700 Years in the Eastern Qaidam Basin, Northeastern Tibetan Plateau

In this study we reconstructed annual precipitation (from July of the previous year to June of the current year) for the past 2500 years in the eastern Qaidam Basin based on well-replicated tree ring width data of Qilan Juniper (Sabina przewalskii Kom.) from living and dead trees and archeological wood from tombs dated back to ~AD 800 or earlier. Megadroughts were identified using the reconstructed series as the periods with consistent below-normal precipitation. The most severe megadroughts reconstructed were centered at AD 1470 and AD 1700, lasting for approx. 100 years. Other less severe droughts were found around AD 370, 480, 550, 700, 790, 1160, 1290, and 1810, lasting for approx. 30-50 years. Using living and dead trees near the upper tree lime, we also reconstructed mean temperature from September of the previous year to June of the current year since AD 130 for the study area. Three severe cold periods were found in the reconstructed temperature record centered at AD 320, 890, and 1600 with each lasting for approx. 100 years. Other cold periods were around AD 540, 820, 1070, 1290, 1500, and 1810, lasting for 50-100 years. We compared the two reconstructed series to discover the characteristics of climate variations (Fig.1). It was found that the warm-wet and cold-dry patterns were the two main modes, while the warm-dry pattern was the less important mode of climate variation in the past 1700 years. For example, the warm-wet climate around AD 600 and during the last 30 years and the cold-dry climate around AD 1290 and 1660 are very prominent. The warm-dry period centered at AD 460, 1180, and 1450 lasted for more than 50 years but with lower magnitude. The climate during the Little Ice Age (AD 1400-1800) is characterized by large variations, with the most severe cold-wet period occurring around AD 1615. In the context of the past 1700 years, the severe drought that impacted North China in the 1920s and 1930s is not among the most prominent dry periods in our study region, while the warm-wet condition during the last 30 years is unsurpassed.