Assessing future climate change impacts on hydrological processes in an agricultural watershed using SWAT+

This study assessed the hydrological impacts of future climate change in the Anseongcheon rural watershed using the SWAT+ model and CMIP6-based multi-model ensemble (MME) data.Two Shared Socioeconomic Pathways (SSP), SSP1-2.6 (low-emission) and SSP5-8.5 (high-emission), were analyzed for the near-future (2040 -2069) and far-future (2070 -2099) periods.To ensure model reliability, calibration (2018 -2019) and validation (2020 -2024) were conducted using observed streamflow data.The average model performance metrics demonstrated satisfactory accuracy, with NSE of 0.62, RSR of 0.64, and PBIAS of -3.05%, supporting the credibility of future projections.Future climate projections from the MME indicate a substantial increase in both precipitation and temperature relative to the historical baseline (1981 -2010).Under the SSP5-8.5 far-future scenario, precipitation is projected to increase by 28.4%, and mean temperature to rise by 5.8°C.Analysis of hydrological components reveals pronounced seasonal variability, particularly under the high-emission scenario.Surface runoff is projected to decrease sharply in spring (-41.07%) and winter (-35.15%),whereas a significant rise in summer precipitation (up to +24.4%) leads to increased surface runoff (+25.89%) and lateral flow (+3.39%).Moreover, strong winter warming results in a remarkable 149.0%increase in evapotranspiration, driven by elevated temperatures despite potential reductions in winter precipitation.Overall, the findings highlight intensified seasonal fluctuations in hydrological processes within rural watersheds under high-emission conditions and demonstrate the robustness of SWAT+ as a tool for supporting adaptive water management strategies in a changing climate.