Assessing integrated circular actions as nexus solutions across different urban challenges: evidence towards a city-sensitive circular economy

Cities across the world are actively exploring the circular economy concept, a key urban planning and design approach for the green transition, simultaneously enabling greater energy and material efficiency and lower pollution, as well as job creation, social inclusion, human health, and well-being. The city can be viewed as a complex socio-ecological system, in which infrastructures and urban forms have co-evolved along with sociocultural practices and the lifestyles of urbanites. Circular design and systemic thinking have not yet been incorporated into the planning and design of the urban built environment, and this limit has progressively created vulnerabilities and risks. Among the various urban resources, available land is often scarce, as it is natural landscape. Consequently, it is particularly important that vacant public space is re-functionalized and brownfield sites are restored. Equally, green infrastructure—urban forests, green roofs, green walls, permeable pavements, and constructed wetlands—provides critical ecosystem services (supporting, provisioning, regulating, and cultural services) at different scales: building, district, city, and region. Green elements and systems in the urban built environment regulate climate, air, and water quality; enable nutrient and water cycling and soil formation; provide space for growing food and for recreation. Using a mixed methods approach, including a literature review and case study analysis, the research identifies several opportunities and challenges to integrated circular actions, “nexus solutions” across various urban challenges, i.e., sociocultural, economic and financial, regulatory, political, institutional, ecological, environmental, and technological. The study then focuses on critical dilemmas faced when implementing nexus solutions. Providing an overview of selected international initiatives, the contribution, leveraging on an extensive interdisciplinary research, aims at showcasing how districts and cities are advancing the circular economy concept in practice. Evidence provided by projects and case studies—such as: Freshkills Park, a landfill reclamation project on Staten Island, in New York City; Royal Seaport, a major urban regeneration project in Stockholm; and Buiksloterham, a neighborhood and an urban living lab in Amsterdam North—are provided, aiming at testing and validating circularity at different scales. The outcomes of the conducted study identify in particular the impacts, both positive (benefits) and negative (trade-offs) of incorporating circularity into the urban planning and design processes, as well as how these can be assessed in order to stir robust systemic change in the long term.