Future projections of thermal and chemical stratifications in reservoir under the impact of climate change

Vertical stratification is a fundamental characteristic of water bodies that significantly affects vertical convection and mixing dynamics. With the impact of climate change, thermal and chemical stratification in lakes and reservoirs has been exacerbated, leading to more pronounced environmental and ecological challenges. While previous studies have identified the impact of climate change on reservoir stratification, they have primarily focused on temperature variations in future periods. This study goes beyond temperature and the direct outputs of General Circulation Models (GCMs) by also considering inflow volume and temperature, providing a more comprehensive assessment of climate change effects on both thermal and chemical stratification. To do so, this study developed a two-dimensional hydrodynamic model, i.e., CE-QUAL-W2, to investigate the thermal and chemical responses of the Wadi Dayqah Reservoir, located in Oman, to projected climate change. The results indicated that under the SSP1–2.6 scenario, the annual mean inflow temperature remained largely unchanged, whereas the SSP2–4.5 and SSP5–8.5 scenarios induced significant increases. Additionally, climate change led to a prolonged persistence of summer thermal and chemical stratification, with the most substantial delay occurring under the SSP5–8.5 scenario. Moreover, the SSP5–8.5 scenario exhibited a significantly higher frequency of critical chemical index occurrences than SSP2–4.5 and SSP1–2.6, highlighting the strong interdependence between thermal and chemical stratification in reservoir systems. Under SSP1–2.6, SSP2–4.5, and SSP5–8.5, thermal stratification (SI) is expected to rise by 12 %, 26 %, and 43 % by the end of the century. The chemical stratification index (CI) is anticipated to climb by 9 %, 21 %, and 38 % in the same scenarios, indicating higher warming routes intensifying stratification. These findings emphasize the urgent need for emission reduction strategies to mitigate climate-induced warming, maintain thermal stability, and protect reservoir ecosystems from extreme stratification under future climate scenarios.