Abstract
Recently collected tree-ring data were used to reconstruct drought from 1700 to the present in four regionsflanking the Great Plains. Regions were centered in Iowa, Oklahoma, eastern Montana and eastern Wyoming.Reconstructions derived by multiple linear regression explained from 44 to 56% of the variance in regionallyaveraged annual precipitation from 1933 to 1977. Years of widespread severe drought clustered into droughtepochs lasting 5-10 years. A weighted mean of the four regional reconstructions pointed out the severity ofthe 1930's drought; the years 1934, 1936 and 1939 ranked among the driest 10 of 278 years. When droughtconditions were averaged over periods of three or more years, the 1930's drought was equaled or surpassedin severity by droughts in the 1750's, 1820's and 1860's. Spectral analysis of the 1700-1977 reconstructionindicated that precipitation averaged over the four regions had a penodicity of 16-19 years, but reconstructions for the individual regions deviated considerably from this result. The Iowa region was dominated bya 22-year periodicity, the Oklahoma region by a 17-23 year periodicity, and the other two regions by arelatively strong 60-year penodicity. Separate analysis of 88-year subperiods of reconstructions indicated thatevidence for a 22-year periodicity was strongest in the most recent period (1890-1977), weaker for 1802-89and lacking entirely from 1714 to 1801.
