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 where balancing the trade-offs across water, energy, and food sectors is especially difficult in resource-deficient areas. The Yellow River Basin is an area in which water shortages lead to conflicts among water, energy, and food resources. Thus, investigating the evolution state and spatial characteristics of the water–energy–food nexus in the Yellow River Basin is essential for the management of resources 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 order degree of the water and energy subsystems in the Yellow River Basin increased by an average of 0.12 and 0.42, on average respectively, from 2004 to 2019, whereas that of the food subsystem only increased by an average of 0.004 compared to the initial year. Furthermore, most prefecture-level cities experienced subsystem degradation of one or two subsystems during the evolution of the water–energy–food nexus system. 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.