2000 years of Drought Variability in the Central United States

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Iowa, Oklahoma, eastern Wyo- ming, and eastern Montana). Although they found the indi- vidual years of 1934, 1936, and 1939 to be among the driest 10 of 278 years investigated (1700 - 1977), they found sev- eral periods of widespread pro- longed drought (3 -10 years) that equaled or surpassed the 1930s drought in intensity and dura- tion: the late 1750s, early 1820s, early 1860s and 1890s. Periods of extreme drought revealed by other dendrochronological as- sessments for the west - central Great Plains coincide with these periods (Weakly 1965; Wedel 1986; Lawson 1970; Lawson and Stockton 1981). Stahle and Cleaveland's (1988) reconstruc- tions of June PSDI in Texas FiG. 3. Paleoclimatic records of Great Plains and western U.S. drought (1600 — present) based on historical and tree -ring data. The pale gray horizontal bars reflect the length of the series, and the dark gray and colored bars indicate periods of drought in 3 -10 -yr increments. Colors mark more widespread droughts that occurred over the same time period in a num- ber of records. The historical droughts are all those reported in the literature. The droughts Showed the most Severe and un- recorded by tree -ring data are those listed in the literature as the most extreme (e.g., the five most severe 10 -yr drou interrupted drought since 1698 accompanied by speci was the 1950s drought, but the twentieth- century drou three driest decades (with some interspersed years of nondrought conditions), by decreasing severity, were 1855 -64, 1950 -59, and 1772 -81. Another dendroclimatic study from the southern plains found prolonged (10 years or more) droughts in Arkansas around 1670, 1765, 1835, 1850, and 1875 that were comparable to twentieth- century events ( Stahle et al. 1985), whereas a study in the Texas — Oklahoma — Arkansas region found the drought of the 1950s was exceeded only in 1860 in the last 231 years (Blasing et al. 1988), a par- ticularly noteworthy year in the historical data, as mentioned above. In a reconstruction of precipitation for the corn belt of Iowa and Illinois, no droughts in the past 300 years were found to be appreciably worse than the 1930s drought, but two were of about the same magnitude (late 1880s -1890s and around 1820) (Blasing and Duvick 1984). Reconstructions of pre- cipitation in Iowa (1640 -1982) indicated that four 10 -yr periods were drier than the period 1931 -1940, and in order of decreasing dryness, these were 1816— 25, 1696 -1705, 1664 -73, and 1735 -44 (Cleaveland and Duvick 1992). Figure 3 summarizes the timing of droughts in these dendroclimatic studies and illus- trates the regional impacts of some of these periods of drought. ght periods in a record). For the few reconstructions that were not fc lists of droughts, periods of drought that equaled or exceeded ghts are shown. The widespread and persistent nature of some of the severe Great Plains droughts of the past three centuries can be compared to twentieth- century droughts using the maps of tree -ring reconstructions of gridded PDSI for the United States (Cook et al. 1996; see maps of other droughts in the past three cen- turies at the NOAA /NESDIS Web site at http: // www.ngdc .noaa.gov /paleo /drought.html). For ex- ample, Fig. 7 shows that the prolonged drought that centered around 1820 appears to be at least equiva- lent in extent and duration to the 1950s drought (Cook et al. 1998). The latter part of the 1750s was also a period of prolonged and widespread drought, comparable to those of the twentieth century. Multiple sources of proxy data, including tree -ring reconstructions and historical records and accounts, work together to confirm the occurrence of several nineteenth - century droughts, as shown in Fig. 6. The 1820s drought is one of several that is documented in the historical accounts of eolian activity (Muhs and Holliday 1995), as well as in tree -ring reconstructions (Lawson and Stockton 1981; Stockton and Meko 1983; Blasing and Duvick 1984; Cleaveland and Duvick 1992; Cook et al. 1998). The drought that oc- Bulletin of the American Meteorological Society 2697