Anthropogenic land-use change in the North American tall grass-short grass transition and modification of near-surface hydrologic cycle

During the 19th and 20th centuries, the landscape of the North American Great Plains was rapidly modified from natural grasslands to agricultural farmlands. These changes affected much of the continent with potential impacts in grasslands equal to deforestation elsewhere. Therefore, the resulting impacts on weather and climate should be studied. In this study, a soil water balance model is applied for 3 land uses at 3 locations, These locations are representative of the east to west declining precipitation gradient of the Great Plains. It was found, in McCook, Nebraska, for example, that annual total evapotranspiration for irrigated maize is 36% higher compared to natural grass. This accounts for an additional 50 million m(3) of water evapotranspired into the atmosphere from an area of 19 000 ha during the growing season, In some instances, Clay Center, Nebraska, and the vicinity evapotranspired nearly 100 million m(3) additional water (compared to a grass covered surface) from irrigated maize during the growing season. Compared to grass, irrigated maize farming elevated soil water in the soil profile, while rainfed maize lowered soil water. This study shows that intensity of the response of soil water distribution in the root zone is a function of vegetation cover and soil physical properties.