Assessment of non-point source loads under climate change and urbanization scenarios using a rainfall-runoff model

ABSTRACT Climate change and urbanization have complex impacts on the hydrological and nutrient cycles of river basins, often leading to an increase in pollutants from non-point sources and the direct loading of pollutants into rivers, which can cause multifaceted environmental problems. Therefore, the purpose of this study was to evaluate the effects of future climate change and urbanization on the loads of major pollutants, including suspended solids (SS), total-nitrogen (T-N), and total-phosphorus (T-P) in the Anseong River Basin in South Korea. The Soil and Water Assessment Tool (SWAT) model was set up and calibrated using observed streamflow and water quality data, indicating satisfactory performance (R2 = 0.72–0.87). Time-series trend analysis showed that SS and T-N loads increased under wet climate and extreme urbanization scenarios. Monthly analysis indicated that higher SS in summer, while T-N and T-P decreased due to reduced infiltration from impervious surfaces. Pollution load duration curve analysis revealed that over 10% of pollutant loads occurred during high-flow events, emphasizing the need to manage first flush effects. This study provides the necessity for establishing future water quality management strategies and customized reduction measures for non-point source pollution.