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<br />2000 Years of Drought Variability
<br />in the Central United States
<br />of
<br />Connie A. Woodhouse" and Jonathan I Overpeck *, +,*
<br />ABSTRACT
<br />Droughts are one of the most devastating natural hazards faced by the United States today. Severe droughts of the
<br />twentieth century have had large impacts on economies, society, and the environment, especially in the Great Plains.
<br />However, the instrumental record of the last 100 years contains only a limited subset of drought realizations. One
<br />must turn to the paleoclimatic record to examine the full range of past drought variability, including the range of mag-
<br />nitude and duration, and thus gain the improved understanding needed for society to anticipate and plan for droughts
<br />of the future. Historical documents, tree rings, archaeological remains, lake sediment, and geomorphic data make it
<br />clear that the droughts of the twentieth century, including those of the 1930s and 1950s, were eclipsed several times
<br />by droughts earlier in the last 2000 years, and as recently as the late sixteenth century. In general, some droughts prior
<br />to 1600 appear to be characterized by longer duration (i.e., multidecadal) and greater spatial extent than those of the
<br />twentieth century. The authors' assessment of the full range of past natural drought variability, deduced from a com-
<br />prehensive review of the paleoclimatic literature, suggests that droughts more severe than those of the 1930s and 1950s
<br />are likely to occur in the future, a likelihood that might be exacerbated by greenhouse warming in the next century.
<br />Persistence conditions that lead to decadal -scale drought may be related to low- frequency variations, or base -state
<br />shifts, in both the Pacific and Atlantic Oceans, although more research is needed to understand the mechanisms of
<br />severe drought.
<br />1. Introduction
<br />Drought is one of the most damaging climate -
<br />related hazards to impact societies. Although drought
<br />is a naturally occurring phenomenon throughout most
<br />parts of the world, its effects have tremendous conse-
<br />quences for the physical, economic, social, and politi-
<br />cal elements of our environment. Droughts impact
<br />both surface and groundwater resources and can lead
<br />to reductions in water supply, diminished water qual-
<br />ity, crop failure, reduced range productivity, dimin-
<br />ished power generation, disturbed riparian habitats,
<br />and suspended recreation activities, as well as a host
<br />*NOAA Paleoclimatology Program, NGDC, Boulder, Colorado.
<br />`INSTAAR, University of Colorado, Boulder, Colorado.
<br />"Department of Geological Sciences, University of Colorado,
<br />Boulder, Colorado.
<br />Corresponding author address: Dr. Connie A. Woodhouse, World
<br />Data Center for Paleoclimatology, NOAA/NGDC, 325 Broadway,
<br />Boulder, CO 80303.
<br />E- mail: woodhouse @ngdc.noaa.gov
<br />In final form i l September 1998.
<br />01998 American Meteorological Society
<br />Bulletin of the American Meteorological Society
<br />of other associated economic and social activities
<br />(Riebsame et al. 1991).
<br />The droughts of the 1930s, 1950s, and 1980s
<br />caused great economic and societal losses in the Great
<br />Plains of the United States, a region particularly prone
<br />to drought (Karl and Koscielny 1982; Diaz 1983; Karl
<br />1983) (Fig. 1). This area shows signs of becoming in-
<br />creasingly vulnerable to drought because of factors
<br />such as the increase in cultivation of marginal. lands
<br />and the escalated use of groundwater from the Ogallala
<br />Aquifer, where water withdrawal has exceeded re-
<br />charge for many years (Glantz 1989; White and
<br />Kromm 1987). Estimates for the return intervals for a
<br />Great Plains drought of 1930s duration and intensity,
<br />based on the properties of the twentieth- century record,
<br />vary from 75 to 3000 years (Bowden et al. 1981;
<br />Yevjevich 1967). Estimates of this type do not pro-
<br />vide a very clear understanding of how rare the severe
<br />droughts of the twentieth century were in the context
<br />of the last 2000 years, nor whether drought of even
<br />greater magnitude is possible. ;
<br />Paleoclimatic data offer a way to evaluate these-
<br />verity, duration, and extent of twentieth - century
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