System dynamics modeling and copula-based risk evaluation of the water–energy–carbon nexus

Rapid urbanization has significantly increased water and energy consumption, leading to escalated carbon emissions and concurrently posing challenges to the water–energy–carbon (WEC) nexus. There is a growing need for integrated approaches to capture the complex dynamics within the WEC nexus and evaluate the integrated risks in future scenarios, thereby synergistically mitigating the pressures on the WEC nexus. This study selected Beijing, heavily reliant on external resources and in urgent need of carbon emission reductions, as a case study. Incorporating socioeconomic impacts, a water–energy–carbon system dynamics model was constructed to simulate the supply and demand of resources and the corresponding carbon emissions. The water, energy, and carbon pressure indices were also predicted to quantify the pressure on each subsystem. Three-dimensional copula functions were subsequently established for integrated risk evaluation. The results reveal that the three pressure indices will exhibit an increasing trend without policy intervention in 2022–2035. With respect to different scenarios, improving utilization efficiency and augmenting the external supply can effectively alleviate water and energy shortages, whereas adjusting the energy consumption structure contributes to reducing carbon emissions. Compared with the baseline scenario, the combined scenario of all the policies performs best among the multiple scenarios, where the risks of water scarcity, energy insufficiency, and excessive carbon emissions decrease significantly to 0.19, 0.06, and 0.05, respectively, and the integrated risk experiences a substantial reduction of 71 %. This study presents a scientific framework for the systematic simulation and risk evaluation of the WEC nexus and provides theoretical support for future policymaking.