2000 years of Drought Variability in the Central United States

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FiG. 8. Paleoclimatic records of Great Plains and western U.S. drought (thirteenth cen- tury through the sixteenth century) based on tree -ring data. As in Fig. 3, the pale gray hori- zontal bars reflect the length of the series, and the dark gray and colored bars indicate periods of drought. Yellow bars mark records that reflect the late fifteenth- century drought, while orange bars mark records that reflect the late thirteenth - century drought. FIG. 9. (a) Location of paleoclimatic records that document the drought. Proxy data reflect the widespread nature of this drought, notable in the Southwest but also detected in records from areas r eastern and southeastern Great Plains to the California coast. Most the duration of this drought was close to 20 yr. (b) Location of pal document the late thirteenth - century drought. Fewer proxy record drought, but most that do exist for this period reflect drought tha duration and that appears to have ranged from the northern Great Pla west, and to the southern end of the Sierra Nevada. The key for th Table 2. these areas as well. For comparison, severe drought con- ditions in 1934 (see Fig. 5) also covered most of these areas, but the 1934 conditions were part of a drought that lasted only several years, as opposed to decades (Karl et al. 1990; Guttman 1991; Cook et al. 1996). c. Evidence for drought, A.D. 1 -1200 The temporal resolution and interpretation of most proxy data for the period A.D. 1 -1200 make it difficult to assess droughts of this period in the same way as more recent droughts. Many of the proxy records that exist for this period extend back several millennia or. more. Because of their great length, even proxy records with annual resolution are typically ana -lyzed in terms of multidec- adal- to century-scale variations. Consequently, our assessment of drought within this time frame focuses on low - frequency (de- cade to century scale) drought variability relative to the twen- tieth century. However, even given this low- frequency per- spective, proxy records suggest that droughts of the period A.D. 1- 1200 occurred on a scale that has not been duplicated since Europeans came to the Great Plains. At least four periods of wide- spread drought between A.D. 1 and 1200 are found in a variety of proxy data from the Great Plains and the western United States as illustrated in Fig. 10. Of these four, the most recent is the least well documented. A late sixteenth - century limited number of proxy records which was especially suggest that a drought began anging from the north- around mid A.D. 1100, although proxy records indicate it is difficult to separate this eoclimatic records that F s are available for this ought from the late thirteenth - t was at least 25 yr in century drought in some of the ins, through theSouth- less finely resolved records. e lettered symbols is in This drought is suggested in the Southwestern archaeological data as a forerunner to the more severe late 1200s drought (Euler et al. 1979; Dean et al. 1985) and is also documented in White Mountains and Four Corners tree -ring records (LaMarche 1974; Rose et al. 1982), in a pre- liminary Colorado Front Range tree -ring chronology (P. Brown 1997, personal communication), and in western Minnesota lake sediments (Dean et al. 1994; Dean 1997). Archeological and pollen data have also been cited as evidence for an onset of markedly drier conditions in the northern Great Plains about this time 2704 Vol. 79, No. 12, December 1998