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Publication Abstract

Atlas of Crop Yield and Summer Weather Patterns, 1931 - 1975 Changnon, Stanley A., Jr., 1982  Illinois State Water Survey, Champaign, IL,  ISWS C-150    Full Text Available

A major phase of the weather-climate research of the Illinois State Water Survey for the past 20 years has concerned the relationships between weather and climate variables and crop production in Illinois (Changnon and Neill, 1967, 1968). Development of expertise in the area of weather-crop modeling, coupled with research interests in the long-range prediction of weather and crop yields, led to a 3-year research project (Huff and Neill, 1980). This project investigated statistical techniques of predicting future corn and soybean yields, for the 45 crop reporting districts found in the 5-state Corn Belt area of Illinois, Indiana, Iowa, Missouri, and Ohio.

One of the by-products of this project, which involved the computerization of the monthly climate data (temperatures and precipitation) and crop yield data, was a classification of these district data into one of three class intervals or terciles: above normal, near normal, and below normal. Corn Belt maps based on these three classes of yields and summer weather variables were then prepared. This report presents selected cartographic results for each year in the 1931-1975 period of study. These patterns are revealing, in a general way, of many important features of crop yield variability, in space and time, and the inherent relationships between July and August weather conditions.

For each year one finds the following material, as classed in the three intervals (above normal, near normal, and below normal), for corn yields, soybean yields (1944-1975 only), July rainfall, July temperature, August rainfall, and August temperature. Production of soybeans across the 5-state area was relatively minor prior to 1944, hence only the results for 1944-1975 for soybeans were used.

The three classifications of above normal, near normal, and below normal relate to the division of the 45-year values of each district into three equal intervals. Thus, the above normal class has the highest 15 yearly values in it. The corn and soybean yield values, before classification into the three intervals, were assessed on the basis of changing technology. That is, a curve was fitted to the yield values from 1931 to 1975 to handle the ever-increasing trend in yields due to technological and/or other improvements. Then each of the 45 yield values was classed according to its departure around the trend line.

The maps are presented in pairs for various yields and weather conditions. Thus, those relating to 1931 and 1932 are presented first, then those for 1933-1934, 1935-1936, etc.

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