PRAIRIE LANDSCAPE CHANGE AND FLOODING IN THE MISSISSIPPI RIVER VALLEY

Extensive landscape alteration of prairie in the U.S. from agricultura l expansion has reduced waterfowl populations and increased precipitat ion runoff into regional river basins. Satellite imagery shows that pr airie landscapes have been less altered in Canada than in the U.S. Lon g-term, broad-scale precipitation data indicate that in both countries precipitation has varied widely but has no increased over time. Never theless, flow rates of unregulated U.S. rivers have increased, but the re have been no detectable changes in flow rates of Canadian rivers. N either of two competing hypotheses advanced to explain increasing floo d magnitude-climate change and channel confinement-can account for the se results. Thus, the increased magnitudes of floods in the Mississipp i River Valley over the last several decades may be at least partially related to extensive changes in agricultural land use resulting in re duction of natural upland vegetation and wetland drainage in the upper reaches of this watershed.