Exploring the water availability and efficiency of inter-basin water transfer projects of urban water supply systems under climate change

Megacities, characterized by their massive and ever-increasing population, exhibit an intense demand for water. Additionally, the impacts of climate change significantly heighten the risk to urban water systems. Capacity expansion projects with inter-basin water transfers are recognized as reliable sources to increase the resilience of megacities where hydrologic conditions are limited. This study presents a novel integrated approach to water resources modeling. It combines a physically-based watershed model with water network simulation software, aiming to assess and enhance the resilience of the Istanbul water supply system against climate-induced challenges. This approach aims to provide a comprehensive understanding of each water transfer scenario's potential impacts and efficacy. Our simulations indicate that without further interventions to reduce water demand and provide strategic resources, the city has a high risk of water scarcity, more likely after the 2050s. Though the new infrastructure development has the potential to substantially increase the security and resilience of the system, there will still be a need to put other alternative sources into practice to match future demand in the late century. This study demonstrates the significance of simulation-based modeling to test planned actions and strategies to evaluate their efficiency in reducing climate-based risks in water supply systems. • Integrated SWAT–Wathnet5 model applied to Istanbul's water supply system. • Reservoir inflows may decline up to 47 % by 2099 under RCP 8.5 scenarios. • Planned inter-basin transfers alone may not meet demand in the long term. • Climate-driven water shortages highlight the need for strategic interventions. • Framework supports long-term planning under climate and demand uncertainty.