Comparative study of climate and human impacts on seasonal baseflow in urban and agricultural watersheds

Abstract

This study explores the long‐term trends of low flow magnitude and the slopes and shapes of the recession curves during winter and summer seasons under climatic and human factors. Four watersheds in the American Midwest are selected for the analysis, including two urban watersheds (Salt Creek and Des Plaines) and two agricultural watersheds (Embarras and Kankakee). The results show that the long‐term baseflow recession slope trends in all the watersheds are primarily induced by human interferences. In the urban watersheds, the recession slopes decrease over time in both winter and summer due to effluent discharges. In the Kankakee watershed with irrigation, the recession slopes decrease in winter but increase in summer, and the opposite winter and summer trends are caused by the seasonal water use regime of irrigated agriculture. In the Embarras watershed with rainfed agriculture, the recession slopes decrease over time in winter but display no change in summer. Sources of water withdrawal (groundwater versus surface water) also have different impacts on the recession process. This long‐term analysis of recession rates, in conjunction with the changes in low flow magnitude, offers valuable insight on human interferences to hydrologic processes. Beyond the specific case studies, this paper documents how a scientific approach based on existing streamflow observation can be applied to improving our understanding of the impact of human and climatic influences on baseflow and low flow processes.