Evaluation of Individual Impacts of Human Activities on Streamflow Changes Using SWAT Model

Understanding streamflow behavior under the influence of climate change and human activities is crucial for developing adaptation strategies and policies for water resource planning and management. However, detecting natural or negligible impact periods is challenging. We aimed to distinguish human impacts on streamflow changes during the affected period using direct data for each human activity by using a hydrological modeling approach in the Gamcheon watershed in South Korea. To this end, a physical-based, semi-distributed hydrological model, the Soil and Water Assessment Tool (SWAT), was applied. The model was set up using climatic and spatial data on watershed characteristics and data on human activities, such as dam operation and water use. Several simulations of runoff, each considering only one human activity, were performed, and the results were compared with those of the naturalized streamflow to determine the individual impacts on changes in streamflow. The combined effects of human activities on streamflow changes were not significant; however, the individual impacts were evident. The 10th lowest flow rate in a year, affected by stream water intake, groundwater pumping, dam operation, and treated sewage water discharge, changed by -13.7%, -54.0%, 34.0%, and 38.4% relative to the natural flow, respectively.