Impacts of climate change on thermal stratification and water quality of Reservoirs

Abstract

Abstract This study examines the impact of climate change on the thermal structure, dissolved oxygen (DO), and phosphate (PO4) values of the Karun IV reservoir, Iran. It covers the baseline period (1995-2014) and future projections (2081-2100). Future meteorological variables were derived from the Canadian Earth System Model version 5 (CanESM5) under two emission scenarios downscaled using a machine-learning approach. The continuous daily inflow of the reservoir over an extended period was simulated by employing the IHACRES rainfall-runoff model, in conjunction with the Water Evaluation and Planning system (WEAP) to replicate water level dynamics and outflow. The evaluation of water quality for the years 2019-2020 was conducted utilizing a calibrated CE-QUAL-W2, and any missing data was approximated through empirical relationships. Our findings indicate that the average surface water temperature and the average PO4 concentration, which respectively stands at 22.8 °C and 0.27 mg/L in the baseline scenario, are projected to increase under both SSP1-1.9 (24.4 °C and 0.31 mg/L) and SSP5-8.5 (26 °C and 0.48 mg/L) scenarios. Whereas the average DO concentration of 8.2 mg/L in the baseline scenario is expected to decline in the mentioned scenarios (7.3 and 6.01 mg/L, respectively). The increase in the temperature of the water and the subsequent decline in DO and PO4 levels in deeper waters pose a significant threat to the sustainable growth of aquatic species in the Karun VI reservoir in the future.