INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. (2014) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/joc.4208 An 850-year tree-ring-based reconstruction of drought history in the western Qilian Mountains of northwestern China Xiaohua Gou, a,b, * Linlin Gao, a,c Yang Deng, a Fahu Chen, a Meixue Yang d and Christopher Still c a MOE Key Laboratory of Western China’s Environmental Systems, Collaborative Innovation Centre for Arid Environments and Climate Change, Lanzhou University, China b Tree-Ring Laboratory, Lanont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA c Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, USA d State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China ABSTRACT: Studies of regional drought history will be helpful for understanding current hydroclimate variability with global warming as well as predicting future hydroclimate shifts. Long-term tree-ring records are scarce in the western Qilian Mountains of northwestern China, which is also the western boundary of the natural distribution of Qilian Juniper (Juniperus przewalskii Kom.) in this area. Here, we present an 850-year (AD 1161–2010) reconstruction of May–July self-calibrating Palmer Drought Severity Index (scPDSI) in the western Qilian Mountains that is based on two nearly millennia of ring-width chronologies derived from long-lived Qilian Juniper trees. The reconstruction suggests a relatively dry phase from the 15th century to the 18th century during the Little Ice Age (LIA) and a relatively wet period over the past two centuries. This reconstruction is consistent with other tree-ring-based hydroclimatic reconstructions from the northeastern Tibetan Plateau, as well as the corresponding century-scale solar activity during the LIA. The three mega-drought periods (AD 1260s – 1340s, 1430s–1540s and 1640s–1740s) recorded by the tree-ring series also correspond to the Wolf, Spörer and Maunder solar activity minimum periods. Results of the multi-tape method analysis and wavelet analysis further confirmed the relationship between regional hydroclimate variability and solar activity forcing. KEY WORDS drought; tree-ring; Little Ice Age; solar activity; Qilian Mountains Received 11 June 2014; Revised 13 October 2014; Accepted 16 October 2014 1. Introduction Extreme droughts and floods have a profound impact on human populations, societies and economies. The fre- quency and intensity of droughts and floods in some areas are predicted to increase in the future (IPCC, 2007), and recent hydroclimatic changes associated with global warming have been documented in many regions of the world (e.g. Treydte et al., 2006; Touchan et al., 2008). For the purposes of accurately understanding current as well as predicting future hydroclimatic changes, it is neces- sary to examine climate history and the climate change forcings. However, meteorological records are limited and short-term in most areas of the world, hampering these studies. High resolution paleoclimatic records (such as tree-rings, stalagmites and lacustrine records and doc- umentations) spanning several centuries can provide a long-term historical context for understanding the climate system, and thus have been widely employed in paleocli- mate research (Chen et al., 2008, 2010). At the regional scale, proxy-based climate variability estimations are still * Correspondence to: X. Gou, MOE Key Laboratory of Western China’s Environmental Systems, Lanzhou University, Lanzhou 73000, China. E-mail: xhgou@lzu.edu.cn scarce for some key regions, such as arid and semi-arid regions where the ecological environment is very fragile and hydroclimate variability is expected to be sensitive to climatic changes. The Hexi corridor area, located in the western Qil- ian Mountains, is a typical arid region in northwest- ern China with average annual precipitation of less than 200mm. Trees from this region are very sensitive to cli- matic fluctuations, particularly hydroclimatic variations. Although there are many dendroclimatic reconstructions from the northeastern Tibetan Plateau (Zhang et al., 2003; Liu et al., 2006; Gou et al., 2010; Shao et al., 2010; Zhang et al., 2011a, 2011b), the long-term tree-ring records are still scarce in the western Qilian Mountains, with pre- vious tree-ring records in this region generally approxi- mately 200 years in length (Tian et al., 2007; Liang et al., 2009; Liu et al., 2009). The western Qilian Mountains are the western boundary of the natural range of the Qilian Juniper (Chen et al., 1994; Yang et al., 2010) in Qilian Mountains, which is a long-lived species native to the northeastern Tibetan Plateau. We wish to examine the hydroclimatic changes in the western Qilian Mountains using the long-lived Qilian Juniper tree-ring materials to evaluate the climate fluctuations of the past millennium, focusing on the medieval warm period, the Little Ice Age © 2014 Royal Meteorological Society