Droughts are one of the most devastating natural hazards faced by the United States today. Severe droughts of the 20th century have had significant impacts on economies, society, and the environment, especially in the central U.S. However, the instrumental record of drought for this region is only about 100 years long and contains only a limited subset of drought realizations. How representative is the 20th century record over time scales of hundreds to thousands of years? Paleoclimatic data offer ways to evaluate the characteristics of 20th century droughts in the context of longer time scales. In this study, a variety of proxy data, including historical documents, tree rings, archaeological remains, lake sediment and geomorphic data, are used to evaluate the representativeness of 20th century droughts compared to droughts which have occurred under the naturally-varying climate conditions of the past two thousand years.
The results of this review of paleoclimatic data suggest that 20th century droughts are not representative of the full range of drought variability that has occurred over the last several thousand years. Proxy data for the Great Plains region indicate that the severe droughts of the 20th century, although certainly major droughts, are by no means unprecedented and it is likely that droughts of a magnitude at least equal to those of the 1930s and 1950s have occurred with some regularity over the past 400 years. A look further back in time reveals evidence that multidecadal drought events occurred in the late 13th and/or 16th centuries that were of a greater duration and severity than 20th century droughts. Other proxy records, including the few annually resolved paleoclimatic records, provide some evidence for longer periods of drought or periods of more frequent drought prior to the 13th century, and support the idea of a drought regime shift roughly around the 13th -15th centuries.
This assessment of the paleoclimatic record suggests that droughts of the 20th century are not unusual in the context of the past 2,000 years, and that future droughts could be of a much greater severity and duration than what we have yet experienced. Assessments of future drought variability should consider the range of natural drought variability of the past several thousand years as documented by the paleoclimatic record, over which possible anthropogenically-induced climate changes will be superimposed