The urban metabolism is a concept which is used in order to analyse how cities work by taking into account the use of resources and infrastructures. This is a method that can help decision makers in understanding the relationship between human activities and the natural environment.
By thinking about cities with a metabolic lens, it is possible to develop material flow diagrams to visualise the typical linear urban metabolism of a city with resource inputs (food, energy, water and so on) and waste stream outputs (food waste, GHG emissions, wastewater and so on). By tracking those flows and their route inside the urban system, an analysis can be carried to spot where the resources are most used, where improvements can be made by diversifying, recycling and cascading, where waste or leakage can be avoided and what kind of interventions must be implemented. This way it is possible to obtain a sustainable circular urban metabolism, where waste outputs become new inputs and drastically reduce a city's environmental impact.
To support a city's resource efficiency transition, the UM is a relevant approach for spatial planning and urban environmental management practices.