Effects of Added Rainfall on the Hydrologic Cycle of Midwestern Watersheds

H Vemon Knapp, Ali Durgunoglu, Stanley A Changnon

Abstract


The effects of added summer rainfall on agricultural areas in Illinois and the Midwest were investigated by using a quasi-distributed-parameter watershed model. Increases in summer convective rainfall during July-August were simulated and used in the model to describe the changes in soil moisture, crop water use, shallow ground water, and streamflow conditions which could potentially result from precipitation augmentation practices. Two periods, representing very dry and very wet conditions, were used in the simulations with 10% to 25% precipitation increases. Results suggest that the greatest proportion of additional summer rainfall eventually percolates into groundwater, and that less than 25% percent of the precipitation increase is used by the crops. Simulated increases in summer rainfall offer limited utility in reducing crop water stress because the rainfall events do not always coincide with the period of greatest crop water need. Methods, such as irrigation, which provide additional water at a specified time and amount produce significant benefits to the plants.

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