Impacts of Climate Change Scenarios on Non-Point Source Pollution in the Saemangeum Watershed, South Korea

Non-point source (NPS) pollution is a primary cause of water pollution in the Saemangeum watershed in South Korea. The changes in NPS pollutant loads in the Saemangeum watershed for an 81-year period (2019-2099) were simulated and analyzed by applying the soil and water assessment tool. Six climate model (BCC-CSM1-1, CanESM2, GFDL-ESM2G, HadGEM2-CC, INM-CM4, and MIROC-ESM) outputs using representative concentration pathway (RCP) scenarios (RCP 4.5 and RCP 8.5) were obtained from the South Korean Asia-Pacific Economic Cooperation (APEC) Climate Center. Simulated streamflow and water quality were evaluated using the Nash-Sutcliffe efficiency (NSE) index and coefficient of determination (R-2). The model satisfactorily simulated streamflow with positive NSE values and R-2 > 0.5. Based on two climate change scenarios (RCP 4.5 and RCP 8.5), gradual increases of 70.9 to 233.8 mm and 1.7 to 5.7 degrees C in annual precipitation and temperature, respectively, are likely for two time periods (2019-2059 and 2060-2099). Additionally, the expected future average annual and monthly streamflow, sediment, and total phosphorus showed changes of 5% to 43%, 3% to 40%, and -55% to 15%, respectively, whereas the expected future average annual and monthly total nitrogen showed decreases of -5% to -27%. Future NPS pollutant loads in the Saemangeum watershed should be managed according to different climate change scenarios.