Mitigating the adverse impacts of climate change on river water quality through adaptation strategies: A Case Study of the Ardak Catchment, Northeast Iran

This study investigates the potential impacts of future climate change on river water quality in Ardak Watershed, Northeast Iran, and proposes adaptation strategies to mitigate adverse effects. The SWAT model is calibrated and verified by Monthly water quality sampling and flow measurements. The premium SWAT-CUP model was utilized for sensitivity analysis and parameter adjustment to simulate runoff, sediment, nitrate, mineral phosphorus, and dissolved oxygen. Future catchment temperature and precipitation were projected using CMhyd statistical downscaling by incorporating four CMIP6 models under SSP scenarios for the near (2025–2049), intermediate (2050–2074), and far (2075–2099) future. The Mianmorgh River experienced increased levels of various pollutants in winter, summer, and autumn but decreased in spring for future periods. In the Abghad River, pollutant levels are expected to increase from late autumn to late winter and decrease in other months. Nitrate increased from the late summer to late winter, then decreased throughout the year. Three adaptation strategies were proposed: reducing rural swage pollutants, creating pasture on 5% of unvegetated land, and combining both. The SWAT model showed responsiveness to the mix scenario, with average reductions of 4—4.5% for suspended solids, 23—16% for inorganic phosphorus, and 16—20% for nitrate for the first strategy. The results revealed that climate change can significantly affect water quality, but its adverse effects can be mitigated with suitable actions. Combined adaptation strategies effectively reduced suspended solids and mineral phosphorus and removed pollutants. Therefore, implementing a combination of effective strategies is more beneficial than individual approaches.