Through the conversion of forests and grasslands to croplands and pasture, humans have affected the transport of water between the atmosphere and land surface. Using IBIS, a global land surface model with 0.5-degree resolution (Foley et al., 1996; Kucharik et al., 2000), and HYDRA, a runoff-routing algorithm with 5-minute resolution (Coe, 2000), we have performed a series of simulations to determine the effects of land cover change on the hydrologic cycle of the Mississippi River Basin.

The IBIS model describes physical, physiological, and ecological processes occurring in vegetative canopies and soils. Through forcing from climate data and vegetation and soil properties, IBIS simulates energy, water, and biogeochemical cycles at small time-steps (30-60 minutes). Lenters et al. (2000) have validated the IBIS-modeled water budget over the Mississippi River Basin at several scales and HYDRA-modeled stream discharge has been compared favorably to United States Geological Survey stream gauge data (Donner et al., 2001). This work extends those studies through the use of an improved version of IBIS. The IBIS model has been calibrated for use over the continental United States through an improved phenology routine and the inclusion of corn, soybean, and wheat as land cover types. Results from a comparison of a control run of natural vegetation with an experimental run of current cover including corn, soybean, and wheat cover will be shown and the significance of land cover conversion to croplands on the hydrologic cycle will be discussed.