Development and Synergetic Evolution of the Water–energy–food Nexus System in the Yellow River Basin

The water–energy–food nexus is a complex system which is especially difficult to achieve as a trade-off in resource-deficient areas. As an area where the shortage of water leads to water–energy–food conflict, investigating the evolution state and spatial characteristics of water–energy–food in the Yellow River Basin is essential for the resource management and sustainable development orientation of the region’s water–energy–food nexus system. This study proposed an integrated assessment framework by using synergy theory and the integrated index system method. The improved Lotka–Volterra symbiotic model was used to elucidate the development and synergy evolution status of the water–energy–food nexus system in prefecture-level cities in the Yellow River Basin between 2004 and 2019. The results show that the development level of water and energy subsystems in the Yellow River Basin increased by 0.12 and 0.42 on average respectively, whereas that of the food subsystem only increased by approximately 0.004 on average compared to the initial year. Furthermore, most prefecture-level cities experienced subsystem degradation for one or two subsystems during the system evolution of the water–energy–food nexus. Based on the uniqueness and evolution process of each city, there are eight possibilities for system evolution and three types of feedback state between each pair of subsystems, which may lead to a certain spatial aggregation. Additionally, the interaction and competition states are more common than synergy states in the water–energy–food nexus system of the Yellow River Basin. This study provides an important basis and suggestions for the internal relationship and sustainable orientation of water–energy–food nexus systems in such water-deficient areas.