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David W. Stahle and Malcolm K. Cleaveland

Tree-ring chronologies can provide surprisingly accurate estimates of the natural variability of important climate parameters such as precipitation and temperature during the centuries prior to the Industrial Revolution. Bald cypress tree-ring chronologies have been used to reconstruct spring rainfall for the past 1000 years in North Carolina, South Carolina, and Georgia. These rainfall reconstructions explain from 54% to 68% of the spring rainfall variance in each state, and are well verified against independent rainfall measurements. In fact, these tree-ring data explain only 6% to 13% less statewide rainfall variance than is explained by the same number of instrumental raingage records. The reconstructions indicate that the spring rainfall extremes and decade-long regimes witnessed during the past century of instrumental observation have been a prominent feature of southeastern United States climate over the past millennium. These spring rainfall regimes are linked in part to anomalies in the seasonal expansion and migration of the subtropical anticyclone over the North Atlantic. The western sector of the Bermuda high often ridges strongly westward into the southeastern United States during dry springs, but during wet springs it is usually located east of its mean position and well offshore. Similar anomalies in the western sector of the Bermuda high occurred during multidecadal regimes of spring rainfall over the Southeast. During the relatively dry springs from 1901 to 1939, the high often ridged into the Southeast, but the western periphery of the high was more frequently located offshore during the relatively wet period from 1940 to 1980. Spring and summer rainfall extremes and decade-long regimes over the Southeast are frequently out of phase, and the tendency for wet (dry) springs to be followed by dry (wet) summers also appears to reflect anomalies in the zonal position of the Bermuda high during spring and summer.

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Matthew D. Therrell, David W. Stahle, and Rodolfo Acuña Soto

Sixteenth-century Aztec codices preserve a record of at least 13 drought years in central Mexico during the prehispanic and early colonial period. Climate-sensitive tree-ring records recently developed for Mexico confirm 9 of the 13 Aztec drought dates, including the extended drought related to the infamous “famine of One Rabbit” in 1454. One Rabbit is the first year of the 52-yr Aztec calendar cycle, and folklore suggests that famine and catastrophe accompany its return. The Mexican treering data indicate that severe drought occurred immediately before 10 of the 13 One Rabbit years during and before the Aztec era a.d. 882–1558. This relationship between drought and the year preceding One Rabbit is statistically significant and suggests a real climatic origin for the “curse of One Rabbit.”

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Falko K. Fye, David W. Stahle, and Edward R. Cook

Instrumental Palmer Drought Severity Indexes (PDSI) averaged over the western United States and Great Plains document three major decadal moisture regimes during the twentieth century: the early twentieth-century pluvial, the Dust Bowl drought, and the 1950s drought. Tree-ring reconstructed PDSI for the contiguous Unites States replicates these three twentieth-century moisture regimes, and have been used to search for possible analogs over the past 500 yr. The early twentieth-century wet regime from 1905 to 1917 appears to have been the wettest episode across the West since A.D.1 500, but similar pluvials occurred in the nineteenth, seventeenth, and sixteenth centuries. The Dust Bowl drought (1929–40) was most severe over the northern Plains to the northern Rockies. No close analogs are found for the full severity and geographical focus of the Dust Bowl drought over the past 500 yr. The 1950s drought (1946–56) was concentrated over the Southwest and was replicated by some 12 droughts of similar spatial coverage and duration over the past 500 yr. One of these analogs, the sixteenth-century mega-drought, was also focused over the Southwest and appears to have surpassed the Dust Bowl drought in coverage, duration, and severity.

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Daniel L. Druckenbrod, Michael E. Mann, David W. Stahle, Malcolm K. Cleaveland, Matthew D. Therrell, and Herman H. Shugart

This study presents two independent reconstructions of precipitation from James Madison's Montpelier plantation at the end of the eighteenth century. The first is transcribed directly from meteorological diaries recorded by the Madison family for 17 years and reflects the scientific interests of James Madison and Thomas Jefferson. In his most active period as a scientist, Madison assisted Jefferson by observing the climate and fauna in Virginia to counter the contemporary scientific view that the humid, cold climate of the New World decreased the size and number of its species. The second reconstruction is generated using tree rings from a forest in the Montpelier plantation and connects Madison's era to the modern instrumental precipitation record. These trees provide a significant reconstruction of both early summer and prior fall precipitation. Comparison of the dendroclimatic and diary reconstructions suggests a delay in the seasonality of precipitation from Madison's era to the mid-twentieth century. Furthermore, the dendroclimatic reconstructions of early summer and prior fall precipitation appear to track this shift in seasonality.

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