Planning circular urban water systems: a Hydrosocial Resource Nexus Framework to support systemic decision-making

Cities are hotspots of climate change, facing growing pressure from droughts, intense rainfall, rising temperatures and resource depletion, particularly in Mediterranean cities such as Girona. Within this context, urban water systems are central to urban environmental management: they move water, energy and nutrients, while being shaped by social, economic and governance conditions. Current planning models still struggle to integrate circular resource flows, multifunctionality and socio-environmental justice, or to translate circular options into concrete structural design decisions. To address these gaps, this thesis proposes the Hydrosocial Resource Urban Nexus (HRUN) framework, which conceptualises urban water management as a multilayer resource nexus linking water, energy, food, ecosystems and society. Within the model, system infrastructure is defined by four design strategies: circularity, scale, greening and digitalisation. The framework sets out a planning cycle for circular interventions and assesses system performance through environmental and socioeconomic functionalities. The research translates hydrosocial and socio-ecological theory into practical planning steps across four studies. First, it establishes the theoretical HRUN planning cycle. Second, it creates an assessment scheme to examine how combinations of the four design strategies affect socio-environmental resilience, including key synergies and trade-offs. Third, it analyses how decentralisation shapes the resilience of drainage, sewage and water-supply subsystems, identifying context-sensitive scales for different circularity purposes and spatial settings. Finally, it tests a spatial decision-support method in Girona, Spain, combining GIS-MCDA, graph-based clustering, risk indicators, socio-environmental criteria and stakeholder preferences. The method prioritises areas for circular water management units based on local vulnerability and appropriate decentralisation scales. The thesis provides a replicable spatial methodology for evaluating infrastructural synergies and trade-offs, linking hydrosocial theory, systems analysis and spatial planning in support of the transition to more just and resilient urban water systems.