Critical review of the energy-water-carbon nexus in cities

Highlights: • A systematic review of the advances in urban energy-water-carbon nexus studies was conducted. • Energy-water nexus analyses at product/sector scale are the mainstream topic. • Energy-water-carbon nexus in cities as an integrated whole is in its infancy. • A unified framework for urban energy-water-carbon nexus is urgently constructed. -- Abstract: Energy, water, and carbon dioxide are interdependent and have complex interactions through the economic supply chains of cities. Reviewing the state-of-art advances in the urban energy-water-carbon (EWC) nexus can help identify suitable tools for EWC management in cities and hotspots for future urban EWC nexus studies. However, systematic reviews of studies on the urban EWC nexus are lacking. This study fills this knowledge gap by conducting a systematic review of the advances in urban EWC nexus studies. The results indicate that nearly 94% of the urban EWC nexus studies focus on the nexus between two of the three aspects, with the 'energy-water nexus' representing the mainstream topic, especially at the product/sector scale (energy/water products or sectors). However, relatively few nexus analyses have been performed for the synergies and trade-offs among the three aspects as an integrated whole. This review reveals that unclear system boundaries of a nexus or city and imprecise urban inner structures may be the main limitations for urban EWC nexus studies. Moreover, the development of a theoretical framework is proposed, and methodological breakthroughs and key research directions urgently needed for urban EWC nexus in the future are highlighted.