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Tree-ring data from the central Plains (the eastern two-thirds of Kansas, the western third of Iowa, and all of Nebraska except the panhandle) were analyzed to create a reconstructed summer (June-August) Palmer Drought Severity Index (PDSI) for the last 600 years. The top graph to right shows how the reconstruction (from 1900-1990) compares to the observed PDSI (from 1900-2003). Although extreme short-term dryness has occurred in this region during the current drought, the long-term drought conditions as measured by the summer PDSI are not as extreme as the observed droughts of the 1950s and 1930s.
The bottom graph to the right shows the individual summer reconstructed PDSI values for each year (gray curve) and the longer-term variations (red 20-year low pass filtered curve) for 1460-1990. The annual values (gray curve) indicate that summer droughts have been as severe during the last 600 years as the most severe 20th century droughts. Of great interest is the indication (red curve) that prolonged severe droughts have occurred in this region, specifically during the 1850s-1860s, early 1800s, and much of the period from 1460 to 1510.
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![]() graph showing reconstructed Palmer Drought Severity Index for Central Plains, 1460-2003 |
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The general methodology of the tree-ring reconstructed Palmer index is discussed by Cook et al., 1999. An earlier version of the PDSI reconstructions is available online from the NOAA Paleoclimatology Branch http://www.ngdc.noaa.gov/paleo/pdsi.html (the data displayed will be available in winter 2004).
Reference: Cook, E.R., D.M. Meko, D.W. Stahle, and M.K. Cleaveland, 1999. "Drought reconstructions for the continental United States." Journal of Climate, 12:1145-1162. |
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