Illinois State Library

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Title

• Long-term variations in seasonal weather conditions and their impacts on crop production and water resources in Illinois

Description

• An analysis of long-term records of corn yields, water resource conditions, and seasonal weather conditions in Illinois found major temporal shifts and important spatial variations in the types of seasonal weather conditions that have positive and negative impacts on yields and water conditions. Nineteen different types of corn-weather seasons (May-August) occurred during 1901-1997, of which nine types accounted for most of the high corn yields (highest 20 of the 97 values) and eight types produced most low yields (lowest 20 values). An assessment of the years with either high or low yields revealed three findings about the distributions of the corn-weather seasons creating these extremes: 1) some types were uniformly distributed throughout the century; 2) others were unevenly distributed over time, some occurring only in the century's early decades and others only in the last few decades; and 3) certain types varied greatly regionally. Yield responses to certain seasonal types varied over time. The findings helped establish that changes in farming practices, corn varieties, and agricultural technology all affect how a given type of growing season affects corn yields. Sizable regional differences in yield outcomes from a given set of weather conditions, a result of varying soil and climate differences across Illinois, further revealed how impacts of similar seasonal weather conditions can vary spatially. These two conclusions revealed the importance of using weather effects in defining seasonal extremes. In general, the statewide results showed that the types of seasons creating high yields predominated during 1901-1910 and 1961-1997, and most seasons creating low yields were concentrated in 1911-1920, 1931-1940, and 1951-1960. Major seasonal weather effects on Illinois' water resources (surface water supplies, ground-water supplies, and water quality) were found to occur in the spring and summer seasons. Two conditions caused these effects in each season: either above normal temperatures and below normal precipitation, or above normal temperatures and precipitation. Spring impacts on water resources were typically mixed, some negative and some positive, whereas impacts from summer season extremes had largely negative impacts on water supplies and water quality. More impacts, positive and negative, occurred in southern Illinois than elsewhere, and most of the seasons having negative impacts on water resources occurred in Illinois during 1911-1960. Comparison of the 1901-1997 temporal distributions of yield extremes (high and low) and the negative summer water resource impacts with the temporal distributions of cyclone passages and the incidence of El Nio Southern Oscillation conditions that affect spring and summer weather conditions revealed a generally good relationship. Periods with many seasons creating numerous negative impacts on corn yields and water resources occurred in several decades (1911-1920, 1931-1940, and 1951-1960) when the number of cyclones was low and most incidences of La Nia conditions that create warm temperatures and negative impacts prevailed. Conversely, when seasonal weather conditions were generally beneficial (1901-1910, 1961-1970, and 1981-1997), Illinois had relatively large numbers of cyclone passages and most El Nio-related cool and wet summers occurred. Consideration needs to be given to the shifting temporal responses to various kinds of seasonal weather conditions during the 20th century to determine how future climatic conditions may affect Illinois' agriculture and water resources. Furthermore, some influential seasonal weather types appeared sporadically, some only during the early decades of the century and others only in the latter decades. Thus, data from the past 97 years reveal that efforts to project impacts of future climate conditions on agriculture and water resources may be difficult and subject to considerable error.

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1. Long-term variations in seasonal weather conditions and their impacts on crop production and water resources in Illinois (20061006190203_ISWSRR-127.pdf).
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