Synergistic management of the water-food-energy-carbon nexus in resource-constrained megaregions: A dynamic general equilibrium assessment for Beijing–Tianjin–Hebei

The intrinsic interlinkages among water, food, energy, and carbon emissions have become a critical factor of regional sustainable development. Under the low-carbon transition, the demand for coordinated policy supply to ensure water, food, and energy security has increased substantially. However, existing general equilibrium analyses of Water–Food–Energy–Carbon (WFEC) nexus policies often lack sufficient policy specificity and systemic coverage, as they tend to overlook dynamic linkages and cross-sectoral transmission processes.To address this gap, this study extends a multi-regional dynamic Computable General Equilibrium (CGE) model by explicitly representing substitution effects among multiple types of water and energy inputs, disaggregating grain production from the agricultural sector, and incorporating a carbon emissions linkage module. Oriented toward prospective policy demands in the Beijing–Tianjin–Hebei (BTH) region, the model is used to design and evaluate water-saving, food production enhancement, energy conservation and carbon reduction, as well as integrated policy scenarios, and to assess their WFEC nexus interaction effects across the three regions.The results indicate that: (1) Single-resource policies targeted at specific objectives involve substantial trade-offs, whereas the integrated scenario (S4) achieves the most synergistic effects across water saving, food production, and energy–carbon mitigation. By 2035, S4 reduces total regional water use by 3.06 %, energy consumption by 0.55 %, and carbon emissions by 2.57 %, while increasing grain produciotn by 0.41 %, at a marginal GDP loss of only 0.02 %.(2)Hebei exhibits the strongest WFEC nexus coupling,with a Policy Comprehensive Impact(PCI) gap between the integrated scenario and single-policy scenarios averages 0.366, compared with 0.447 in Beijing and 0.373 in Tianjin, and further narrows to 0.273 by 2035.(3)Effective WFEC nexus governance in the BTH megaregions requires synergistic, region-differentiated coordination framework, in which Hebei serves as the primary adjustment area for integrated regulation, while Beijing and Tianjin play complementary and stabilizing roles within the coordinated policy portfolio.