THE 1920S DROUGHT RECORDED BY TREE RINGS AND ...

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404 ERYUAN LIANG ET AL.and of these climatic proxies, trees growing in the arid or semi-arid regions canprovide annual or seasonal records of drought events through the study of theirannual rings (Fritts, 1976; Bradley and Jones, 1992; Schweingruber, 1996). Unlikethe general descriptions of drought disasters in historical records, high-resolutionprecipitation reconstructions using tree rings and other climatic proxies can providequantitative estimates of anomalous rainfall deficiency. In several case studies,tree-ring data has successfully reproduced the severe and sustained drought of the1660s and 1579–1598 in the Upper Colorado River Basin (Meko et al., 1995), themegadrought of the 16th century in North America (Stahle et al., 2000), the LostColony and Jamestown droughts in the southeastern USA (Stahle et al., 1998) andthe prolonged droughts in 1429–1519 and 1634–1741 in the northeastern TibetanPlateau (Shao et al., 2005). In addition, tree-ring networks can provide a pictureof temporal and spatial patterns of past drought events (Fritts, 1974; Hughes andGraumlich, 1996; Villalba and Veblen, 1997; Cook et al., 1999), enabling scientiststo learn more about the characteristics of droughts.China is subject to a strong monsoon climate with precipitation varying greatlyfrom year to year and from season to season (Zhang and Lin, 1992). In some years,rainfall is abundant enough to cause flooding, while in other years there is toolittle rain to support agriculture from region to region (http://www.mwr.gov.cn/english1/20040802/38161.asp). Thus affected by monsoons and topography, Chinais one of the countries with the most frequent drought and flood hazards in theworld (http://w.mwr.gov.cn/english1/20040802/38161.asp). According to the reportof damage in China (1949–1995), among all disasters, droughts lead to thegreatest economic loss (Damage Report, 1995). Based on the dryness/wetness indicesin eastern China over the last 530 years, studies found that the dry and wetanomalies initially appeared in northeastern China and then migrated to affectsouthern China (Hu and Feng, 2001; Qian and Zhu, 2001). The regional characteristicsof interannual and interdecadal variability are also outstanding. A quasi-20aand a quasi-70a oscillation exist in temperature and precipitation series in differentregions over China, but wet and dry spells occur in an opposite phase in the northand the south (Qian et al., 2003). The 1920s was the driest decade in northern Chinaof the past 120 years, and this dryness coincided with elevated temperatures (Xu,1997; Wang et al., 2004a).The identification of links between tree growth and documented drought eventsallows us to determine how accurately tree-ring records reflect drought occurrence.The 1920s drought was the most severe and well-recorded natural hazard in thelast 200 years in the semi-arid and arid areas of northern China (Xu, 1997). Avariety of historical records including newspapers, unpublished reports, and booksabout natural hazards in each province documented the 1920s drought and itssocial impact (Deng, 1937; Li et al., 1994). Based on the historical record, Li et al.(1994) considered the 1928–1930 drought to be one of the top ten natural disastersin modern Chinese history (1840–1949). Also recently, Xu (1997) analyzed thepossible social and natural factors leading to the great famine in the 1920s and early
THE 1920S DROUGHT IN NORTHERN CHINA 4051930s in Northwest China. Based on dryness/wetness indices in the past 500 yearsin Northwest China, Dong et al. (2000) found that severe droughts, including the1920s drought, usually started in South Ningxia and central Gansu (see Figure 1),and then expanded to Northwest China. The hydrological station in the middlereaches of the Yellow River also showed an 11-yr low-flow period from 1922 to1932 (Shi et al., 1991; Liu and Wu, 1996). In comparison with the 1930s DustBowl in the southern plains of the USA (Worster, 1982; Woodhouse and Overpeck,1998), most studies of the 1920s drought have been based on historical records inChinese and have received scant mention in international journals (Hughes et al.,1994; Fu et al., 1999; Qian and Zhu, 2001; Liang et al., 2003). Recently, severalstudies have also reported that the 1920s drought in northern China was recorded intree rings (Hughes et al., 1994; Zhang and Wu, 1997; Liu and Ma, 1999; Liang et al.,2003; Liu et al., 2004). These studies were, however, limited to a few forest standsin North China. Moreover, most dendrochronological studies in China have beenconfined to climatic reconstructions of a single or just a few tree-ring sites, and todate no large-scale drought or precipitation reconstructions have been completed.The development of a tree-ring network in recent years and the availability ofdocumentation of the well-recorded 1920s drought provide a rare opportunity tocapture the links between the growth of drought-sensitive trees and documentedevidence of drought, and to thus examine the possibility of recovering past largescaledrought events using tree rings.In this study, fourteen tree-ring chronologies, four precipitation and two moistureindex series derived from tree rings in the semi-arid and arid areas of northernChina were selected for analysis. The detailed historical records concerning theeffect of the 1920s drought on agriculture, society, and hydrological systems wereemployed to demonstrate the intensity, duration and spatial extent of the 1920sdrought, allowing for a comparison to be made with drought-related informationderived from a large-scale tree-ring network.2. Study Areas, Climate and Tree-Ring Network2.1. STUDY AREAS AND TREE-RING NETWORKThe study areas are the semi-arid and arid regions of northern China (Figure 1).Along an east-west orientation, the drought-prone forest sites were selected from theTaihang and Yinshan Mountains in North China (Region 1), the Qinling Mountains(Region 2), the Qilian Mountains (Region 3), the mountains in the east margin ofthe Qaidam Basin (Region 4), the South Qinghai Plateau (Region 5), the east TianshanMountains (Region 6) and the middle-west Tianshan Mountains (Region 7)(Figure 1). The distance between the most eastern forest site (XWT) in Region 1and the most western forest site (ZL) in Region 7 is about 2825 km. Based on administrativedivisions in China, tree-ring sites are situated in six provinces in North
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