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Publication Abstract

Temporal Distribution of Midwestern Precipitation during the 20th Century Changnon, Stanley A., 2003  Illinois State Water Survey, Champaign, IL,  ISWS DCS 2003-01    Full Text Available
Temporal fluctuations in the annual and summer precipitation across the Midwest during the 1898-2002 period are defined and described. Precipitation amounts were assessed for 15-year periods to show how patterns of precipitation have shifted spatially over the 20th Century. The early part of the century featured near average precipitation conditions, followed by predomi-nately dry conditions from 1928 through 1957. For example, during 1928-1942, 96 percent of the Midwest had below average precipitation. After 15 years with near average conditions from 1958 to 1972, extremely wet conditions developed during 1973-2002, with 91 percent of the Midwest experiencing above average precipitation. Extreme precipitation values sampled during each 15-year period revealed temporal differences with much more extreme amounts during wet and dry periods than during near average periods. Annual totals reflected the long-term variations in summer rainfall, revealing the importance of summer rainfall in determining annual amounts. Regionally, amounts were below average more frequently in the southern Midwest than in the central and northern Midwest. Values were above average more frequently in the northern Mid-west than in the central and southern Midwest. The results provide information that should be useful for hydrologic and agricultural planning and assessments.

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