be suitable for energy-efficiency retrofits (for example, historic structures) and buildings waiting for energy- efficiency renovations and other adaptations to enhance environmental sustainability and climate readiness (Dávi et al. 2016; Mokhtara et al. 2019; Kim et al. 2020; Moran, O’Connell and Goggins 2020). Distributed generation, energy storage technologies and climate-ready grids can also contribute to efficient energy supplies, especially in the developing world, where vast numbers of buildings currently lack access to energy infrastructure. Local projects like these can benefit from collaborative governance schemes at the local, regional and national levels (de Reuver, van de Lei and Lukszo 2016; Winfield and Weiler 2018). If the energy and materials footprints of residential and commercial buildings and offices need to be reduced and their lifecycles extended to serve additional generations of users, this can be done through modifications, redesign and retrofitting. Any reductions in energy use and environmental impact would also offset the environmental footprints of substandard housing, especially in informal settlements. Such improvements may increase as rising household incomes and government subsidy programmes incentivize investment in housing quality, infrastructure, utility service provision and opportunities for land and homeownership to improve the quality of life and resilience of all dwellers.


Under this dimension, buildings would collect and use rainwater on-site. Greywater and rainwater could be reused by buildings themselves through living walls and green roofs, with multiple benefits, such as passive cooling, air filtering and improved aesthetics (Pradhan, Al-Ghamdi and Mackey 2019). They could also be used around the city, collecting, treating and reusing them as locally as possible to limit the need for water imports from elsewhere (Yoonus and Al-Ghamdi 2020). Nature-based solutions such as bioswales could retain water on-site to support local landscapes and habitats, while rainwater harvested on rooftops or through other small-scale systems could become a resource, rather than a nuisance to be rapidly disposed of downstream


70 GEO for Cities


(Khirfan, Peck and Mohtat 2020). These types of water resources can improve access to drinking water from public supply systems, particularly for residents in informal urban settlements or refugee camps, and create storage during heavy rainfall. Moreover, using small-scale systems decreases stress on stormwater infrastructure and reduces the risk of overflows and floods, as shown by strategies being implemented in Mexico City (Tellman 2019), Wuhan (Dai et al. 2018) and Singapore (Brears 2020).


The idea of circular cities does not imply that the introduction of new technologies will be free from impacts or that levels of consumption will need to decline equally across all regions and cities. This would be fundamentally unjust, since millions of poor people need to increase their consumption of goods and services and will need to do so for some time to come in order to thrive. While we need absolute advances in aggregate efficiency of urban resource use, these would likely be distributed differently across different populations. Some people and cities would need to reduce their consumption patterns and become much more circular to decouple products or services from their environmental impact, while others would continue to consume in a linear fashion and avoid waste through both innovative and traditional methods and technologies for waste reduction, recycling and avoidance. There are two key areas in which measures to make cities more circular are imperative: urban metabolism (arising from production and consumption patterns) and buildings.


Urban metabolism


The term urban metabolism refers to how cities import resources, circulate them through production and consumption subsystems, and generate waste as residuals. The resources imported by cities include energy, water, nutrients and other organic materials, as well as a wide range of products with embodied resources and processed materials. The production and consumption systems range from manufacturing and technology, public and consumer


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