Modeling variations in soil moisture and streamflow resulting from climatic and land use changes

A distributed parameter watershed model IWASCH has been developed to simulate variation in soil moisture and baseflow conditions for agricultural areas in Illinois, resulting from climatic and land use changes. The model incorporates components sensitive to water movement process. To preserve the accuracy of the hydrologic processes within the model, calibration takes place on two levels - for both soil moisture and total streamflow. Once a number of soil types are calibrated, no major calibration is needed for other watersheds which contain the same soil types. Because of its properties as being a portable and distributed parameter model, it has a potential for use in analyzing the effects of climatic change and land use changes on the watershed hydrology. Simulations are presented for a small Illinois watershed for 1) irrigation over the entire watershed; and 2) moderate precipitation augmentations. The relative effects on soil moisture, crop water use, shallow groundwater, and streamflow conditions are compared. The major hydrologic differences occur as a result of the timing of the application of water, with irrigation having controlled applications and rainfall augmentation being uncontrolled.