Scenario Simulation and Comprehensive Evaluation of Coupling Coordination Relationship Between Regional Water Use and Water Environmental Protection: A Case Study of Tianjin, China

Water use and water environmental protection exhibit highly complex interactions, and their coupling coordination is essential for long-term urban sustainability. This study analyzes the system structure of water utilization, and constructs a water resources–social economy–water environment (WR-SE-WE) system dynamics model for Tianjin and five policy scenarios (business as usual (BAU), water conservation prioritization (WCP), social–economic advancement (SEA), water environmental protection (WEP), and integrated balanced development (IBD)) are simulated. A coupling coordination degree (CCD) model is employed to evaluate scenario performance. The key results show that Tianjin’s WR-SE-WE CCD keeps increasing but differentiates for different scenarios: IBD consistently outperforms all scenarios, achieving an optimal coupling coordination degree of 0.926 by 2035, while the other scenarios rank SEA (0.920) > WEP (0.902) > BAU (0.880) > WCP (0.874). The indicators’ quantitative results exhibit single-policy scenario trade-offs: WCP maximizes water efficiency and pollution control, but severely constrains social economy, offering a temporary solution. WEP excels in water resources supply but limits GDP growth, serving as an effective interim measure. SEA drives rapid economic expansion but strains resources and delays pollution control, making it suitable for long-term planning. Combining the obstacle degree model, four recommendations are proposed, including implementing cross-sector water governance, accelerating the green industrial transition, prioritizing reclaimed water, and scaling agricultural efficiency. These results provide a scientific basis for promoting high-quality regional development in the future.