Water-Energy-Food-Ecosystem nexus assessment: interactions between Scale, Circularity, Greening, and Digitalization in Urban Water Systems design

Urban Water Systems (UWSs) play a vital role in the Water–Energy–Food–Ecosystem (WEFE) nexus. This study explores how four design strategies—scale, circularity, greening, and digitalization—interact to influence urban metabolism flows, energy demand, and ecosystem services within hydrosocial systems. While these strategies are critical to sustainable UWSs, their synergies and trade-offs remain underexplored. Using a structured literature review and a systems approach, we mapped interdependencies among them, with an explicit focus on circular interventions—namely water reuse, resource recovery & reuse (R-RR), and water-cycle restoration (WCR). We outline an intervention typology matrix that can be operationalized for qualitative impact assessment in future case studies. The study highlights context-dependent outcomes and the need for an integrated design perspective to balance trade-offs, reduce environmental impacts, and maximize sustainability outcomes within the WEFE nexus.