Quantifying the effect of land use land cover change on increasing discharge in the Upper Mississippi River

There is convincing evidence that land use/land cover (LULC) change has contributed to increasing discharge in the Upper Mississippi River Basin (UMRB) but key details remain unresolved. In this study, we extend our previous work (Zhang and Schilling, 2006) to quantify how much of the increasing discharge was due to LULC change. We examined daily streamflow for the 1890-2003 period from the US Geological Survey stream gage at Keokuk, Iowa and compiled county agricultural statistics for soybean production in the watershed above the gage to quantify how much of the change in the relation of discharge to precipitation was due to increased soybean cultivation. By allowing the slope of the discharge-precipitation relationship to be a function of the area of the UMRB planted in soybean, we determined that increasing soybean acreage increased the slope of q_t- P_t by 32%. With row crop expansion anticipated from ethanol production, increasing agricultural production is expected to result in increased water yield and nutrient export. Results provide important benchmarks for assessing the significance of LULC change on the regional water and climate patterns in the UMRB.