System dynamics modelling to simulate regional water-energy-food nexus combined with the society-economy-environment system in Hunan Province, China.

Nexus approaches provide an efficient way to analyze the dynamic evolution of the water-energy-food nexus (WEFN), yet there is a need to close the science-policy divide by making simulation models more practically relevant. This study incorporates society, economy and environment systems (SEE) into the WEFN, simulating a broad environmental system. A system dynamics model is constructed to simulate and dynamically track the development of the WEF-SEE system in Hunan Province, China. The developed model is applied to assess WEF-SEE system trajectories from 2021 to 2035 against nine policy goals formulated by the Hunan Provincial Government. Baseline results suggest that Hunan Province will have a surplus of grain production and will be in a state of "self-sufficiency" in water resources. The energy security situation is not as optimistic, with imports being required to meet demand. The sustainable development of the WEF Nexus will be constrained by resource shortages. As the future development of Hunan Province outpaces environmental protection policies, water pollution and CO emissions and are expected to increase. Intra-system trade-offs and synergies under the impacts of different policies indicate that the implementation of an indicative policy has the intended impact within its particular subsystem, but may lead to trade-offs in other subsystems. Due to system interconnectedness, the simultaneous implementation of multiple policies may increase or hinder progress towards certain goals. For example, expanding planting area increases food production, but increase agricultural water demand and water pollutant discharge, counter to water security goal and environmental protection goals. Cross-system impacts must be considered when choosing policies. This study advances environmental system analysis and evaluation, and contributes to practical policy recommendations, providing useful insights for Hunan Province, especially considering potential trade-offs and synergies. Such information could lead to more effective, holistic environmental policy formulation.