This work serves as three-fold contribution to foster the transition towards circular economy in cities. Circular economy (CE) is taken as paradigm to approach sustainable development –betterments in social, environmental and economic dimensions– throughout the complex and dynamic urban structures. Applying the concept to the city level merges two highly potential adjuvant elements to an effectively functioning urban system –a space which might generate even higher success than as so far could be reached with a circular business.
However, recent practical approaches to bring a circular city alive are in their very first steps. Transformation happens by turning the respective city into one that embraces and embeds CE. The ideal illustration represents a system where all stakeholders (businesses, the society and the government) exchange and manage urban stocks and flows (physical, social, institutional, informational and monetary) in way that results in the best overall outcome. The fundamental prerequisite is to have a common understanding of the desired state to be reached and measurements supporting precise communication and targeted action. Departing from a holistic and ideal definition of a circular city, an indicator set with 42 indicators (incl. four alternative indicators) quantifying and qualifying measurable and for a circular city relevant urban stocks and flows has been developed. It serves as basic means to capture the individual state and performance of the respective city. Those are assigned to three categories –the three striving states of a circular city– which are: the improvement of environmental regeneration by incrementally reducing material flows with CE principles which demand to cycle and to cascade materials within the biosphere and technosphere, the enhancement of social well-being that includes assurance of environmental quality, material conditions, life quality and empowering of civic participation, and finally economic quality of an economy which considers society and environment as determining elements. An index formula is finally proposed that expresses following criteria: social and environmental improvement that occurs unrestricted and decoupled from economic growth. By setting these states into relation, the index finally indicates the effectiveness of the city assessed.
Through the application of the developed circular city indicator set and index to the city of Aalborg, Denmark (DK) and New York, United States (US), the preceded conceptualization is contextualized. Both cities are frontrunners in sustainable urban development and actively approach the transition towards CE. Besides assessing the cities themselves, they are contrasted while insightful lessons learned, informing especially about the readiness of cities to measure their performance, which is extremely impeded by data inconsistency and unavailability on the city level, are demonstrated as well. Conclusions are hoped to lay the stepping-stone for further research and practical investigations in this area.