services, and finance and business services through to food and building materials. Supporting circular urban metabolisms requires a comprehensive approach that increases efficiencies for urban systems through changes in individual, sociocultural, and managerial and operational business practices. It also requires structural changes, such as closed-loop systems across industrial and consumer markets, alongside the corresponding infrastructure (especially in countries and economies where these loops do not currently exist). Moreover, the resources and materials that may form part of these closed circular loops must also be available (see example from Kerala, India, in chapter 5). These changes in practices may accelerate with the introduction of new technologies to improve absolute efficiencies within urban sociotechnical infrastructure and those that influence social processes, market structures, regulatory regimes and governance arrangements (IRP 2018). By coupling urban integrated planning and resource management, a metabolic shift can achieve results that would not be possible through isolated interventions or business-as-usual approaches. These changes are necessary because if we stay on our current path, by 2050 total urban resource consumption across the world would reach about 90 billion tons, 50 to 60 per cent more than the estimated global urban and rural energy and material consumption for 2000 (IRP 2018).


Given current urban land use, density and form, a combination of resource-efficient technologies and a range of actions, from building designs and codes, renewable energy generation and transportation through to waste management would be required. Notwithstanding the uncertainties inherent to estimating the potential scale of these combined interventions, a clear positive outcome is likely: under a resource-efficient scenario, cities may reduce land use by 5 to 20 per cent, metal consumption by 5 to 30 per cent, water consumption by 35 to 50 per cent and greenhouse gas emissions by 30 to 50 per cent (IRP 2018). A scenario based on more strategic densification,4 with transportation playing a bigger role, could improve these results, reducing land use by 20 to 40 per cent, metal consumption by 30 to 50 per cent, water use by 36 to 60 per cent and greenhouse gases by 40 to 60 per cent (IRP 2018).


Implementing an urban metabolism approach requires many coordinated measures (Figure 4.1), from managing urban inflows through to progressively reducing and closing urban outflows (measures also comprise improvements to urban form, urban densities and land-use planning, as discussed in the second dimension), including:


v end-of-life regulations for consumer and industrial products, starting with the ones with the largest impacts on urban metabolism (particularly energy flows);


v consumer products that can be returned to producers for material recovery, with recovered materials used to feed closed-loop production systems using innovative


4 Strategic densification can be described as a process of intensifying the number of jobs, people and amenities, and thus of mixed land uses, located within a network of primary and secondary relatively high-density nodes that are well-connected by efficient, sustainable and affordable mass transit systems and infrastructure for active transport.


industrial ecologies tailored to social and cultural context, and physical, financial and institutional infrastructures to support markets for recovered materials;


v formalizing the collection of waste and recyclables, partnering with or incorporating workers from the informal economy into recycling operations by offering training, safe and healthy working conditions, and living wages (for European examples, see the Urban Waste project; for a Latin American experience, in Medellin, Colombia, see the reports on life quality published by Medellin Cómo Vamos);


v improved and standardized models of material flow analysis and life cycle assessment that can assess, monitor and identify the changes needed in the urban circular economy footprint, which, when linked together, can capture the non-linear and complexity of these material flows. To build trust in these results, the data for these models and the modelling itself should be overseen by independent entities, such as universities, and follow a common methodology.5


Measures to support the transition to this circular urban metabolism include establishing material exchanges, funding recycling centres based on the best available technology and offering jobs and training. Lisbon provides an example of transitional steps to create matrix models of energy and water (Agencia de Energía e Ambiente de Lisboa [AEAL] 2015; AEAL 2016) as does the Plan Économie Circulaire for Paris based on an urban metabolism approach (Agence dÈcologie Urbaine not dated; Mairie de Paris 2017).


Developing circular urban metabolism models and data- collection protocols can also contribute to the shift (Petit-Boix and Leipold 2018; Dijst et al. 2018; Lavers Westin et al. 2019; Lucertini and Musco 2020). Examples include the models and simulation tools developed by the Global Initiative for Resource Efficient Cities, particularly the Spatial Microsimulation Urban Metabolism tools and the UNEP Urban Circularity platform, as well as the participatory urban metabolism mapping and analysis toolkit developed by Ecocity Builders and its partner organizations. The durability of construction materials and building design also needs to be improved, while allowing for reuse and recycling and avoiding construction material waste. Many cities are already on this pathway and have made major commitments under the C40 Zero Waste Declaration.


Efficient and reusable buildings A wide mix of strategies is essential to maximize building efficiency in terms of energy, water and waste. These include standards for reusing and rehabilitating vacant housing and dilapidated infrastructure, as well as retrofitting existing architecture. These approaches may require policy interventions from the state. Buildings also constitute “mines” of raw materials for further use, with the potential to harvest, recycle and reuse their components at the end of their useful life. Performance standards and commitments for retrofitting are particularly relevant in this area.


5 These entities and their corresponding knowledge platforms can support the principle of additionality in urban transformational agendas over multiple political cycles (World Climate Research Programme 2019; Delgado 2021; Solecki et al. 2021). On the ground, local governments and NGOs can use participatory approaches to implement data collection and analysis initiatives.


Cities that Work for People and Planet


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