Changes in non-point source (NPS) pollutant loads in the Mankyeong watershed for the 30-year future period (2011-2040) were assessed with consideration of the uncertainties in theclimate change scenario data. The six major variables from ten Global Climate Models (GCMs)and one Regional Climate Model (RCM) for the Representative Concentration Pathways(RCP) 8.5 scenario were used for downscaling and bias correction using the non-parametricquantile mapping method. Then, the downscaled weather variables were used as input to thecalibrated and validated Soil and Water Assessment Tool (SWAT) model for simulating thechanges of future NPS pollutant loads. The bias-corrected data appropriately reproduced thespatial and temporal patterns of the NPS pollutant load which was derived using observedweather data. The rates of change in sediment, total nitrogen (TN), and total phosphorus(TP) loads within each subwatershed under the RCP8.5 future scenario showed an averageincrease of 13.1 to 142.5%, –13.4 to 49.5%, and 0.40 to 127.6%, respectively, compared tothe pollutant load based on the multi-model ensembles (MME) mean for the historical period(1976-2005). It can be concluded that sediment and TP loads are sensitive to changes in thecharacteristics of climate variables by showing increase trend in most of the subwatersheds.In addition, the possible uncertainty range based on minimum and maximum values for thesediment, TN, and TP loads were quite wide, showing -50.8 to 367.3%, -34.5 to 196.3%, and-49.9 to 284.1%, respectively. Looking at the temporal distribution, the uncertainty ranges forboth sediment and TP were higher during the wet season from June to September. Therefore,it will be necessary to develop adaptation measures for reducing the impacts of climate changeon NPS pollution, considering that NPS pollutant loads are very sensitive to the changes inclimate variables.
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