Ecological network analysis for urban physical-virtual water cycle: A case study of Beijing

Growing water demands have increasingly challenged the urban water cycle resilience. In contrast to conventional evaluations, which concentrate primarily on the physical water cycle, this study presents a methodological framework considering both physical and virtual components and chooses Beijing as a case study. We constructed an urban physical-virtual water cycle (PVWC) network model to investigate water cycle resilience through structural and functional analysis based on ecological network analysis (ENA). The PVWC model covers multiple water suppliers (surface water, groundwater, transferred water, and reclaimed water), multiple water users (production water use, domestic water use, and ecological water use), water leakage, and wastewater treatment, as well as physical links and virtual flows driven by trade among these nodes. This study analyzed the system's robustness and the contributions of individual components to overall resilience from structural dimension, as well as revealed dominant sectors and interrelationships between components that sustain the system's resilience from functional dimension. The case study of Beijing in 2017 demonstrates that its network is moderately robust and synergistic. The external water transfer subsystem mainly has more remarkable mutualistic pair-wise relationships with secondary industry, tertiary industry, and household consumption. Moreover, water distribution subsystem is the dominant controller of PVWC, while the through flows of water leakage and wastewater treatment rely on the operation of whole system. The ecological environment, which has strong connections with reclaimed water and ecological water flows, played an important role in the entire system promoting more mutualistic relationships. We found that increasing the proportions of transferred water and reclaimed water supply and promoting mutualistic interactions between water users are critical to improving urban water cycle resilience.