Evaluating the synergies of water resources, water environment, water ecology, and water security nexus in China: an integrated water management perspective

To China's prominent practical dilemma of fragmented departmental water management, mismatched resource–environment–ecology–supply risk governance, and unbalanced regional water endowment, the coordinated development of water resources, water environment, water ecology, and water security (Four-Water Integration (FWI)) has become a pivotal localized path for China's characteristic integrated water governance. Targeting fragmented, separated, and partial implementation drawbacks in existing FWI practical management, this article establishes a four-dimensional quantitative evaluation framework. Combining the entropy weight and coupling coordination degree (CCD) model, we quantify subsystem synergistic performance across 31 provincial-level regions of the Chinese mainland from 2010 to 2022. Results indicate that indicators with high data discrimination capacity include per capita water resources, waterlogging control area, and surface water quantity, while the water security subsystem shows the strongest data differentiation among the four subsystems. China's FWI nexus is currently in a state of imbalance. This study suggests formulating differentiated, targeted, and forward-looking policies, improving urban water circulation systems, and expanding the utilization of unconventional water resources. This study enriches the theoretical system of water governance and provides a scientific basis for optimizing the sustainable water development. This empirical work supplements quantitative evidence on China's FWI spatiotemporal imbalance and delivers differentiated policy enlightenment for domestic water regulation and global developing-country integrated water governance.