Decoupling the Water–Energy–Food–Carbon Nexus in Beijing, China: Interactive Mechanism and Policy Simulation

Water, energy, and food (WEF) are essential resources for sustaining urban development, yet their production and consumption generate substantial carbon dioxide (CO2) emissions. Carbon-reduction policies designed to curb these emissions have profound impacts on WEF systems by reshaping both the resource production and consumption patterns. This study employs system dynamics (SD) modeling to examine the mutual interactions between the WEF system and carbon emissions through scenario analysis for the period of 2016–2030. A WEF–carbon SD model comprising 76 variables is developed and calibrated using data from 2016 to 2023. The results show that under the business-as-usual (BAU) scenario, energy consumption continues to increase, while CO2 emissions rise slightly from 87.2 million tonnes in 2023 to 88.7 million tonnes in 2030. In contrast, under the economic optimization scenario (e.g., through industrial structure adjustments), water consumption will be reduced by approximately 100 million cubic meters by 2030 compared with the BAU scenario. Energy consumption declines by about 7%, food production decreases slightly by 4%, and CO2 emissions are reduced by 7.9%. Furthermore, land-use changes will enhance the carbon sequestration capacity by 12.67% in 2030, while exerting only marginal effects on CO2 emissions (less than 1%) and water consumption. Overall, this study enriches the existing WEF–carbon nexus modeling and provides policy-relevant insights for Beijing to reduce carbon emissions from an integrated WEF perspective.