| The Mississippi Basin is the third largest drainage basin in the world and is home to one of the most productive agricultural regions on Earth. In order to face land and water resource challenges in the coming decades, we need to understand and quantify how the relationships between land surface characteristics and energy, water, and nutrient cycles might change with land cover change, changes in land management, and climate change.; A coupled land surface/ecosystem model and runoff-routing algorithm (IBIS-HYDRA), adapted for use at a regional scale, was used along with high-resolution crop cover maps to examine the effects of agricultural land cover change on the surface water balance and river hydrology of the Mississippi River Basin. This modeling system enabled the first examination of the hydrologic effects of continental-scale land cover change involving the explicit representation of different types of natural vegetation (forest, grassland, savanna) and different types of crops (corn, soybean, wheat). The results of the simulated changes were compared with the magnitude of hydroclimatic anomalies associated with the El Nino-Southern Oscillation (ENSO) phenomenon.; The land cover change simulations show that the effects of conversion from preagriculture vegetation cover to the current mosaic of natural vegetation and croplands depend on time, place, climate, soil type, and the particular conversion (specific natural vegetation type and specific crop type). The simulation results suggest that the replacement of grasslands with croplands may have very different effects on the surface water balance than deforestation. The simulation results show that the magnitude of evapotranspiration and total runoff changes associated with ENSO is generally on the order of changes resulting from land cover change. While La Nina has a stronger effect on Mississippi Basin streamflow, the anomalies associated with El Nino are comparable to those resulting from land cover change. These results suggest that human beings are able to alter the regional hydrologic cycle at magnitudes comparable to natural variability, but further study is needed to determine how land cover change and climate variability interact to produce hydrologic changes. |
