Intensified pluvial conditions during the twentieth century in the inland Heihe River Basin in arid northwestern China over the past millennium Chun Qin a , Bao Yang a,b, ⁎, Iris Burchardt c , Xiaoli Hu a , Xingcheng Kang a a Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Donggang West Road, 730000 Lanzhou, China b MOE Key Laboratory of West China's Environmental System College of Earth and Environment Sciences, Lanzhou University, Lanzhou, Gansu, China c Institute of Geography, University of Erlangen, Kochstrasse 4/4, D-91054 Erlangen, Germany abstract article info Article history: Received 3 November 2009 Accepted 14 April 2010 Available online 25 April 2010 Keywords: tree rings dendrohydrology streamflow variability the Heihe River arid northwest China last millennium Past streamflow variability is of special significance in the inland river basin, i.e., the Heihe River Basin in arid northwestern China, where water shortage is a serious environmental and social problem. However, the current knowledge of issues related to regional water resources management and long-term planning and management is limited by the lack of long-term hydro-meteorological records. Here we present a 1009-year annual streamflow (August–July) reconstruction for the upstream of the Heihe River in the arid northwestern China based on a well-replicated Qilian juniper (Sabina przewalskii Kom.) ring-width chronology. This reconstruction accounts for 46.9% of the observed instrumental streamflow variance during the period 1958–2006. Considerable multidecadal to centennial flow variations below and above the long- term average are displayed in the millennium streamflow reconstruction. These periods 1012–1053, 1104– 1212, 1259–1352, 1442–1499, 1593–1739 and 1789–1884 are noteworthy for the persistence of low-level river flow, and for the fact that these low streamflow events are not found in the observed instrumental hydrological record during the recent 50 years. The 20th century witnessed intensified pluvial conditions in the upstream of the Heihe River in the arid northwestern China in the context of the last millennium. Comparison with other long-term hydrological reconstructions indicates that the intensification of the hydrological cycle in the twentieth century from different regions could be attributable to regional to large- scale temperature increase during this time. Furthermore, from a practical perspective, the streamflow reconstruction can serve as a robust database for the government to work out more scientific and more reasonable water allocation alternatives for the Heihe River Basin in arid northwestern China. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Water resource management requires knowledge of the natural variability in streamflow on different time scales (Fritts, 1976; Li, 2000; Case and MacDonald, 2003; Woodhouse and Lukas, 2006; Yuan et al., 2005). In China, today's water resource planning is based primarily on recent hydrological records. Unfortunately, these records are typically shorter than 100 years in length and contain only a limited portion of the spectrum of natural hydro-climatic variability. This limits projections of future water resource variability and long- term planning and management of water resources, since it is expected that anthropogenic effects will strongly modulate natural streamflow variability (Huang, 1985; Li, 2000; Kang et al., 2002; Bradley 2008; Jonathan et al., 2009). In addition, past hydrological conditions are of particular importance for a critical test of climate models, given that many models used for future climate simulations do not accurately simulate modern precipitation regimes (Bradley, 2008). Tree-ring-based hydrological reconstructions have been widely used to extend existing instrumental streamflow records (Stockton and Meko, 1975; Smith and Stockton, 1981; Cleaveland and Stahle, 1989; Baldazo, 1995; Meko and Graybill, 1995; Li, 2000; Meko et al., 2001, 2007; Woodhouse, 2001; Woodhouse and Meko, 2002; Kang et al., 2002; Case and MacDonald, 2003; Meko and Woodhouse, 2005; Yuan et al., 2005; Woodhouse et al., 2006; Woodhouse and Lukas, 2006; Akkemik et al., 2008; Saito et al., 2008). An outstanding case is the Colorado River streamflow reconstruction (Woodhouse and Meko, 2002; Meko and Woodhouse, 2005; Meko et al., 2007), which successfully identified a megadrought event before 1490 in this region. In China, a number of dendrohydrological reconstructions have been established (Li et al., 1997; Li, 2000; Yuan et al., 2005; Gou et al., 2007). These reconstructions, however, are mainly obtained from the westernmost part of arid north- western China (Xinjiang region) and only span several hundred of years. In this study, we have accomplished a 1009 a streamflow Global and Planetary Change 72 (2010) 192–200 ⁎ Corresponding author. Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Donggang West Road, 730000 Lanzhou, China. Tel.: + 86 931 4967538; fax: +86 931 4967488. E-mail address: yangbao@lzb.ac.cn (B. Yang). 0921-8181/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.gloplacha.2010.04.005 Contents lists available at ScienceDirect Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha