Millennium tree‐ring reconstruction of drought variability in the eastern Qilian Mountains, northwest China

Global mean surface temperatures have risen by 0.85 ± 0.20 °C, over the period 1880–2012, and projections of future climate change suggest further global warming (IPCC 2013). Warming of the global climate is expected to be accompanied by increase of global precipitation, as warmer air is able to hold more water vapour (Wentz et al. 2007). However, precipitation changes are expected to differ from region to region: precipitation is likely to increase at high latitudes, the equatorial Pacific Ocean and many mid-latitude wet regions, and decrease in many already dry mid-latitude and subtropical regions (IPCC 2013). In the arid northwest China, Shi et al. (2007) found that the region has become wetter in the last several decades. However, the data they used are typically limited in length, which hampers our understanding of the trend of long-term hydroclimatic variability in this region, and how this variability may be changing in a warming world. Therefore, long-term hydroclimatic variability derived from highresolution paleoclimatic proxy data, like tree rings, lake deposits, ice cores and historical documents, are invaluable. Among these, annually resolved and precisely-dated treering data are most commonly used. Tree-ring based hydroclimate reconstructions have been developed for numerous sites around the globe (Cook et al. 2010). However, in the eastern Qilian Mountains, the tree-ring chronologies reported so far are mostly based on Qinghai spruce (Picea crassifolia Kom.) and span less than two centuries (Deng et al. 2013), which are barely sufficient to study the patterns of climate variability at multi-decadal and centennial timescales. Luckily, Qilian juniper (Juniperus przewalskii Kom.) is also found in this region. Qilian juniper is one of the most successful tree species for dendroclimatology in northwestern China, and had been used to reconstruct the Abstract Knowledge of natural long-term drought variability is essential for water resource management and planning, especially in arid and sub-arid regions of the world. In the eastern Qilian Mountains of China, long-term drought variability based on high-resolution proxy records such as tree-ring data are still scarce to date. Here we present a new tree-ring chronology from the eastern Qilian Mountains which provides a valuable 1,002-year record (1009–2010 CE) of drought variability. The new reconstruction of June– July 5-month scale standardized precipitation and evapotranspiration index is the first millennium tree-ring estimate of past climate developed in the eastern Qilian Mountains. The record shows that this region has experienced several persistent droughts and pluvials over the past millennium, with significantly drier climate during the fifteenth century and dramatic wetting since the nineteenth century. The low frequency generally agrees with other nearby studies based on both tree-ring data and other proxy data.