Circular Cities

Why talk about circular cities?

Cities are major places where social, economic and environmental activities take place. Consequently, the way they are designed and managed affects the quality of life of citizens, the efficiency of economic operations, and the health of ecosystems.

Comparable to living organisms, cities represent complex systems with their own metabolism. Indeed, the concept of “urban metabolism” encompasses all materials and raw materials needed to sustain the lives of its inhabitants.

To date, cities consume about 75% of natural resources, are responsible for 60-80% of greenhouse gas emissions, and produce more than 50% of global waste. This underlines the key role of cities in the ecological transition, addressing environmental challenges such as climate change, commodity dependence, biodiversity loss, and waste management.

Adopting circular practices within the city can have a significant impact on environmental sustainability and community well-being by creating sustainable and resilient urban environments. 

A number of major metropolises around the world have already come together in a network called C40 Cities. This has the aim of disseminating, collaborating and encouraging in the adoption of actions to counter the climate crisis. To be part of this organization, cities must have met a set of standards with minimum requirements. They need to ascertain the mayors’ commitment to promoting concrete policies and actions against climate change.

What is a circular city?

A “circular city” is defined as a city that actively promotes the transition from a linear to a circular model. This happens through collaboration with researchers, residents and businesses. In line with the Sustainable Development Goals defined by the UN therefore, circular cities are committed to reducing emissions, fostering biodiversity and reducing social inequalities by applying the principles of circular economy and environmental and social sustainability. In a circular city, efforts are made to minimize resource extraction, focusing instead on recovering waste materials so that they are not waste but become a resource. In order to realize this model, systemic thinking and collaboration between actors must be fostered leading to environmental, economic and social benefits.

To introduce cities to all available strategies for a circular transition, ICLEI, Circle Economy, Metabolic and the Ellen MacArthur Foundation have developed the Circular City Actions Framework. The Framework is based on concrete actions in which cities can engage, and can be applied to all production, consumption, and waste management processes in which cities and residents are involved. The Circular City Actions Framework merges the 3 principles of circular economy outlined by the Ellen MacArthur Foundation, the Model of R’s, and the Key Elements developed by Circle Economy. Specifically, it is based on 5 complementary strategies:

• Rethink: A circular city must commit to re-designing and re-imagining the entire system so as to form the basis for circular activities.
• Regenerate: Encourage infrastructure, production and supply systems that allow nature to thrive. This will protect and restore biodiversity and will also have a positive impact on the well-being of residents and the city itself, making it better equipped to adapt to climate change.
• Reduce: Minimize material, water and energy use and waste generation from production to end of use. In a phrase, “doing better, with less.”
• Reuse: Extend the life of existing resources, products, spaces and infrastructure. This will reduce total waste and relocate the economic value of materials, contributing to the local economy.
• Recover: Maximize the recovery of resources at the end of the use phase and reintroduce them into production processes. This will eliminate emissions and negative environmental impacts that result from landfilling and waste incineration processes.

Practices that can be adopted by circular cities

Early attempts to include circular economy principles in urban policies and strategies focused on waste or resource management plans. More recently, circularity has been linked to climate strategies. For instance, in Tampere, Finland, it is part of the sustainability plan with the Action Plan for zero emissions by 2030, while in several cities in Sweden, circularity is a tool to achieve carbon neutrality goals, fostering innovation and new business models.

At the implementation process level, the European Union’s Circular Cities and Regions initiative (CCRI) has developed a methodology to implement circular solutions at the city level. The proposed process consists of three steps: map the territory and understand its metabolism, define circular solutions and implement them.

In the context of urban metabolism analysis, in order to adopt circular practices, it is essential to identify the key sectors in terms of waste generation on which it is strategic to intervene, starting with the measurement of circularity.

Recent studies focus on an in-depth investigation of these sectors through the analysis of material flows, subsequently outlining strategies for the urban transition to a circular economy. An example of this is the “Circular Rotterdam” study developed in 2018 by Metabolic on commission from the municipality. This type of approach was also implemented in “Taranto Circolare“, a project developed by Tondo in 2024.

For what concerns European projects, on the other hand, the focus is on individual key areas for a specific city. For example, City Loops, funded by EU Horizon 2020, aims to make material flows circular in seven European cities, focusing on demolition and construction waste and biomass waste. Similarly, the Reflow project tested approaches to urban circularity in six pilot cities in Europe, each focusing on different resource flows, such as municipal waste, food, textiles, and wastewater.

Regarding the definition of circular solutions, there are various practices at different levels that a circular city can adopt to deserve this designation. Some examples are given below:

• Sustainable urban planning: Everything starts with circularity-oriented urban design and efficient use of resources. A concrete example is the city of Stockholm (Sweden), specifically the Hammarby Sjöstad District. The latter was designed following the concept of “closed-loop” metabolism, which encourages synergies between water, energy and transportation services. For example, the district is heated by purified wastewater, combustion of household waste, and biofuel. In addition, the biogas produced is used to run local transportation vehicles.
  
• Sustainable mobility: A sustainable city should promote the use of low-emission public transportation. it is also important to provide adequate electric mobility infrastructure and integrate soft mobility infrastructure such as bicycle lanes and pedestrian areas to the city. Sharing services and creation of traffic-restricted zones to encourage walkability can be a good incentive for more sustainable mobility habits.
  
• Waste Management and Recycling: Implementing separate collection and recycling systems and using innovative processes to treat waste. One example of Waste Management is in Helsinki, Finland, which is known for having one of the most advanced and automated underground waste management systems in the world, using a series of pneumatic tubes to collect waste from different parts of the city and transport it to a central processing facility. Helsinki currently has more than 800 collection points that transport more than 20 tons of waste per day.
  
• Renewable energy and energy efficiency: it is the responsibility of a circular city to adopt and support the implementation of renewable energy sources for energy supply. This is critical with a view to improving the energy efficiency of buildings and infrastructure, and in the long run can lead to zero- or even positive-impact buildings. Local institutions can also support city businesses and residents through incentives and funding to adopt more efficient solutions.
  
• Urban agriculture and food security: a circular city should actively promote sustainable agricultural practices within the city. To reduce transport-related carbon emissions and support local farmers, a circular city can engage in communicating to its citizens the importance of consuming locally produced food. Furthermore, for the long-term well-being of residents, circular cities can encourage the creation of green spaces, urban gardens and vertical cultivation, thus improving air quality and fostering biodiversity. Finally, the Reflow pilot project launched in Milan in 2019 shows how it is essential to adapt the consumption system to the current lifestyle in order to achieve a circular food system.

Circular Cities

Leading cities such as Amsterdam, Paris, Copenhagen and Barcelona are developing strategies for the circular economy at the urban level. Some, such as Amsterdam and London, have defined real action plans for the transition to circularity. In particular, Amsterdam aims to halve the use of raw materials by 2030, achieving the vision of becoming fully circular in 2050.

Circular Amsterdam

In 2020, Amsterdam launched the plan “Circular Amsterdam. A vision and action agenda for the city and metropolitan area” embracing the circular economy and setting ambitious targets to reduce environmental impact and improve liveability.

The plan includes more than 70 actions to be realised in cooperation with entrepreneurs, social initiatives and residents. The municipality will work with businesses and organisations to facilitate the adoption of circular principles by providing individual support and networking.

In particular, the strategy focuses on two key urban waste-producing sectors:

• Construction sector: Amsterdam City Hall aims to build 70,000 new houses by 2040 with a circular construction approach. This can lead to a 3% increase in productivity (EUR 85 million/year) through the reuse of materials. This could generate 700 new jobs in the near future. The strategy foresees a saving of 500,000 tonnes of materials, reducing CO2 emissions by 0.5 million tonnes/year. The four main strategies include smart design, efficient disassembly, high-value recycling and the creation of a resource and materials market and bank.
• Organic waste: in Amsterdam, high-value treatment of residual organic fractions could generate an added value of EUR 150 million/year in 5-7 years. By collecting only household organic waste, protein for animal feed, biogas and materials for the chemical sector could be produced, reducing CO2 emissions by 600,000 tonnes/year. This scenario could create 1,200 new jobs in the long term. The four main strategies include a central hub for the biorefinery, waste separation and return logistics, optimisation of the organic waste stream and nutrient recovery.

City Circular Hubs

In order to implement circular economy strategies at the urban level, not only from a planning and policy perspective, the development of Circular Hubs, understood as physical spaces that act as incubators for good circular practices within urban fabrics, represents an approach to adopt circular practices from a bottom-up perspective, promoting innovation and community involvement.

Significant examples in this context can be found in the Netherlands, where Blue City, for instance, transformed a disused swimming pool into a circular economy centre for the city and region in 2015. Furthermore, De Ceuvel, an office park built on the site of a former shipyard in the north of Amsterdam, has become an internationally recognised case study in the circular economy. With 17 workspaces, the site has been conceived as a ‘clean technology playground’ with numerous practical examples of decentralised technologies and recycling of local resources.

A relevant example in this perspective is the 22@ district in Barcelona, where the transformation of the former industrial district of Poblenou into a technological district, home to innovative companies and start-ups, is an ideal ground for experimenting with the implementation of regenerative circular economy strategies involving local production centres and makers.

Measuring the circular city

Nowadays, thanks to digital technologies, it is possible to monitor resources in detail: keeping an eye on the situation and the progress made is of paramount importance to optimize their use and ascertain the state of achievement of one’s goals, to then set increasingly challenging sustainability goals.

In this regard, measuring circularity in cities is also key to the transition to a sustainable society.

In order to assess the level of circularity of cities, the analysis is carried out on a macro level and the data required is significantly greater than for a single organization. In fact, it is necessary to use databases in order to carry out more complex analyses, both because of the volume of data and the multiplicity of systems considered.

The concept to be considered is that of “urban metabolism“, and there are currently several methods for determining this.

At the European level, the measurement of urban circularity is supported by initiatives such as the CCRI Methodology, or within the City Loops project that has outlined 29 frameworks of analysis to study urban metabolism.

Most of the methodologies used to date are based on material flow analysis (MFA), a tool capable of identifying flows and stocks within a given system, adopting a linear approach.

This methodology makes it possible to determine within a system the economic activities with the greatest impact in terms of resource consumption. These indications, together with an analysis of the quantities of CO₂ equivalents linked to extraction and production activities, make it possible to define the complete picture of material consumption and air emissions.

There are different types of MFA, among them the EW-MFA (Economy-wide material flow accounts) is the methodology implemented by EUROSTAT.

In line with this approach, other less popular but historically important methods analyse the interdependence between economic sectors and activities, such as in Input-Output Analysis (IOA).

In addition to linear models, there are dynamic approaches that are ideal for interpreting complex systems such as cities. Among these, the MuSiasem method (Multi-scale integrated analysis of societal and ecosystem metabolism) focuses on the connections between various socio-ecological aspects of the systems considered, representing one of the most interesting framework tools currently available.

As can be seen, the methodologies available for examining material, energy and emission flows at urban and territorial levels are diverse, with general or specific, linear or dynamic approaches.

This type of analysis often also includes urban indicators related to key sectors, allowing the degree of circularity of a city to be assessed. This facilitates the evaluation of the impact of specific proposals and initiatives in certain policy areas.

A significant example is the second edition of the Circular Cities Barometer, launched in 2023 by Holcim and Bloomberg Media, which highlights the leading global cities leading the transition to a circular economy. The Circular Cities Barometer methodology evaluates cities based on circularity of buildings, systems, lifestyles and leadership.

In general, it is crucial to develop shared indicators to obtain comparable data and to compare different cities on the same level.