2000 years of Drought Variability in the Central United States

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FIG. 5. Comparison of observed and tree -ring reconstructed PDSI values for two of the most extreme drought years in the twenti- eth century, 1934 and 1956. Although the severity of these droughts is not fully captured by the tree -ring reconstructions, the recon- structions duplicate the spatial extent and duration (see Fig. 6) of these droughts. Images are from the NOAA/NESDIS Web site (see text) (Karl et al. 1990; Guttman 1991; Cook et al. 1996). sources. These data provide evidence to support the droughts documented in the few available extralong Great Plains tree -ring records, as well as for the pe- riod prior to that covered by tree -ring reconstructions. Locations of these proxy records are shown in Fig. 4b and described in Table 2. Thus, although the rapid decline in the number of annually resolved drought records prior to about 1600 makes it difficult to resolve interannual variations in drought frequency and mag- nitude, paleoclimatic records can provide key con- straints on the full range of natural decadal to interdecadal drought variability. During the thirteenth to sixteenth centuries, there is evidence for two major droughts that likely signifi- cantly exceeded the severity, length, and spatial extent Bulletin of the American Meteorological Society of twentieth - century droughts. The most recent of these "megadroughts" occurred throughout the west- ern United States in the second part of the sixteenth century. The dendrochronological records that reflect this drought and their locations are indicated in Figs. 8 (time line) and 9a (map, key in Table 2). This drought is indicated in a southwestern Nebraska chronology (Weakly 1965) as well as in. a reconstruction of Ar- kansas drought (Stahle et al. 1985). Weakly (Wedel 1986) notes two periods of what he terms "very se- vere" drought, from 1539 to 1564 and from 1587 to 1605. Stahle et al. (1985) suggest that the period 1549- 77 was likely the worst drought in Arkansas in the past 450 years. Other tree -ring reconstructions for the broader western United States reflect this drought, 2699