2000 years of Drought Variability in the Central United States

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tos, vi SCALEI:12500000 0 100 200 700 400 800 KRAM ETERS Fic. 1. Advanced Very High Resolution Radiometer Data (AVHRR)-derived I -km land cover map of the Great Plains (Townshend et al. 1994). Large portions of this area, used for both agriculture and livestock grazing, are highly susceptible to drought. droughts in the context of the past two millennia (e.g., Overpeck 1996). In this review paper, we bring to- gether evidence of a greater range of drought variabil- ity than found in the instrumental record, from all available sources of paleoclimatic data, including his- torical documents, tree rings, archaeological remains, lake sediment, and geomorphic data, to evaluate the representativeness of twentieth - century droughts in terms of those that have occurred under naturally vary- ing climate conditions of the past several thousand years. The persistence of drought- causing atmospheric conditions is examined through a review of the cur- rent literature on- ventieth- century droughts; as well as through an examination of whether base - state shifts and low - frequency variation in oceanic /atmospheric systems can yield the persistence needed for the multidecadal- to century-scale droughts of the past. Finally, the prospects of future drought are considered, both in view of the full range of past natural drought variability, and in terms of land use practice and hu- man greenhouse gas— induced climate change. 2694 a. Seventeenth— nineteenth century drought in the Great Plains Temperature and precipitation records, extending from 1851 to 1890, exist for early meteorologi- cal stations and forts in the Great Plains but are quite fragmented and patchy. Data (locations are shown in green on map in Fig. 2) have been analyzed by Mock (1991), who determined that no drought since 1868 has been as severe as that of the 1930s. However, due to the scarcity of records, he was unable to make a full assessment of a drought in 1860, which may have ex- ceeded the severity of the 1930s drought. Historical accounts from newspapers and diaries provide addi- tional documentation of nineteenth - century drought events. The 1860 drought was reported in Kansas newspapers, which continued to mention the severity of this drought for several decades after the event (Bark 1978). Less severe droughts were also reported in historical documents and early meteorological records for several years around 1860, in the late 1880s, and in the early 1890s (Ludlum 1971; Brad- ley 1976; Bark 1978). The map in Fig. 2 shows gen- eral locations of data sources and drought years documented in historical data, while Fig. 3 (top) shows a time line of these droughts. Accounts of early explorers document periods of blowing sand (an in- dication of drought conditions) for an- area extending from northern Nebraska to southern Txas (Muhs and Holliday 1995). These areas are shown in brown in the map in Fig. 2, along with dates of documented Vol. 79, No. 12, December 1998 2. Poleoclimatic evidence for Great Plains UIa drought, A.D. 1 -1900 URBAN OR BUDS- LPUU3! A variety of paleoclimatic data MS"` sources can each be tapped to pro - j U1RJ<,ATMCRQK NND&.'DPAMMS vide key insights into Great Plains I 3PASg_vUSMU8I+,M drought. Taken together, these 9 SAVANNA proxy data offer a much more com- FOREST plete picture of natural drought variability than offered by instru- WATER Boo= mental data or any one proxy BARRIN OR SPARSMY VEisTAIW source alone. A summary of proxy paleodrought data sources and their characteristics is given in Table 1. SCALEI:12500000 0 100 200 700 400 800 KRAM ETERS Fic. 1. Advanced Very High Resolution Radiometer Data (AVHRR)-derived I -km land cover map of the Great Plains (Townshend et al. 1994). Large portions of this area, used for both agriculture and livestock grazing, are highly susceptible to drought. droughts in the context of the past two millennia (e.g., Overpeck 1996). In this review paper, we bring to- gether evidence of a greater range of drought variabil- ity than found in the instrumental record, from all available sources of paleoclimatic data, including his- torical documents, tree rings, archaeological remains, lake sediment, and geomorphic data, to evaluate the representativeness of twentieth - century droughts in terms of those that have occurred under naturally vary- ing climate conditions of the past several thousand years. The persistence of drought- causing atmospheric conditions is examined through a review of the cur- rent literature on- ventieth- century droughts; as well as through an examination of whether base - state shifts and low - frequency variation in oceanic /atmospheric systems can yield the persistence needed for the multidecadal- to century-scale droughts of the past. Finally, the prospects of future drought are considered, both in view of the full range of past natural drought variability, and in terms of land use practice and hu- man greenhouse gas— induced climate change. 2694 a. Seventeenth— nineteenth century drought in the Great Plains Temperature and precipitation records, extending from 1851 to 1890, exist for early meteorologi- cal stations and forts in the Great Plains but are quite fragmented and patchy. Data (locations are shown in green on map in Fig. 2) have been analyzed by Mock (1991), who determined that no drought since 1868 has been as severe as that of the 1930s. However, due to the scarcity of records, he was unable to make a full assessment of a drought in 1860, which may have ex- ceeded the severity of the 1930s drought. Historical accounts from newspapers and diaries provide addi- tional documentation of nineteenth - century drought events. The 1860 drought was reported in Kansas newspapers, which continued to mention the severity of this drought for several decades after the event (Bark 1978). Less severe droughts were also reported in historical documents and early meteorological records for several years around 1860, in the late 1880s, and in the early 1890s (Ludlum 1971; Brad- ley 1976; Bark 1978). The map in Fig. 2 shows gen- eral locations of data sources and drought years documented in historical data, while Fig. 3 (top) shows a time line of these droughts. Accounts of early explorers document periods of blowing sand (an in- dication of drought conditions) for an- area extending from northern Nebraska to southern Txas (Muhs and Holliday 1995). These areas are shown in brown in the map in Fig. 2, along with dates of documented Vol. 79, No. 12, December 1998