Background: Provision, use and consumption of resources are usually considered merely with regard to specific products or services. However, a systemic understanding is needed for sustainable development – not least in the case of resources of the soil-sediment-water system. The concept of urban metabolism tries to integrate all urban material flows, stocks, loops and their internal and external interdependencies in a comprehensive way.
Urban metabolism – according to urbanmetabilism.org – is the study of material and energy flows arising from urban socioeconomic activities and regional and global biogeochemical processes. The characterization of these flows and the relationships between anthropogenic urban activities and natural processes and cycles defines the behavior of urban production and consumption. Urban metabolism is therefore a deeply multi-disciplinary research domain focused on providing important insights into the behavior of cities for the purpose of advancing effective proposals for a more humane and ecologically responsible future.
Goal: Through a comprehensive understanding of urban material flows, stocks and loops and their environmental impacts the concept aims to develop practically useful strategies, tools and instruments to enhance urban resource efficiency, consistency and sufficiency and to minimize direct and indirect negative environmental impacts that are initiated by urban areas.
 
Rationale from the themes: Demand: Urban areas are the central habitats of humanity, especially in Europe where around 75 % of the population lives in cities. Hence, urban areas are hubs of resource consumption. Nearly all materials in cities are more or less directly from soil (may it be from agriculture, forest or mining activities – all having environmental impacts). These consumption activities are based on demand of the urban population for food, energy, water, housing, infrastructure and a variety of products and services. It’s predicted that in 2030 about 80 % of global consumption will be generated by urban areas. Enormous material flows are initiated by urban activities (i.e. through the construction sector) which lead to a high consumption of the materials itself (i.e. natural resources) but also of scarce land.
Natural Capital: To satisfy the requirements for resource consumption, natural resources and land/soil are needed. But these resources are limited and some of them are very scarce, which increases the limitation furthermore. Worldwide, the natural capital (e.g. minerals, biomass) is mostly exploited to satisfy the needs of the urban areas, because people and their consumption needs accumulate there as described above. Hence, enormous resource flows are initiated through activities in urban areas (driving force) and this in a very complex way (several factors need to be considered). This leads to land consumption (e.g. for mining or agriculture) and consumption of natural resource (e.g. for construction). The concept of urban metabolism could be used to monitor the initiated resource flows, also with regard to the global hinterland. It is crucial to understand the urban resource flows, their driving forces, their ecological effects and their impact on consumption of land and natural resources regionally and worldwide. The urban metabolism is a very useful methodological concept which could serve as basis for this process understanding.
Land Management: The enormous resource flows that are initiated through consumption activities in urban areas challenge the global resource basis and aggravate the limitation of scarce resources. This likely leads to a non-sustainable development which is based on consumption and growth without the recognition of ecological, social and economic limits. It is crucial to solve this trade-off between urban consumption and resource depletion. Instruments and strategic tools are needed to enable a more sustainable management of urban resource flows under the premise that urban quality of life is ensured.
However, the cities are also becoming spots of intense accumulation of resources. In the infrastructures, landfills and urban buildings enormous resource stocks were built and measures are needed to re-/use these stocks effectively, e.g. with urban mining activities. Here, efficient regulations including health and safety rules are needed in as much as an awareness of the potentials. Another critical management task relates to the optimization of the logistical handling of resources – in particular their storage.
Urban metabolism as an analytical tool could identify potentials for a more resource efficient way of urban activities (e.g. through the realization of an urban circular economy). It’s also possible to include aspects of consistency (e.g. materials used for construction) and sufficiency (e.g. the consumption behavior of people) into the strategic instruments or overall framework based on the knowledge which is generated through the understanding of the urban metabolism.
 
Net Impact: Strategic tools and instruments that are based on the concept of urban metabolism should be able to identify the critical stocks and flows of materials and resources. In a comprehensive assessment, they should also address externalities and negative ecological, social and economic impacts that occur indirectly or unconsciously. This includes rebound effects of efficiency measures, indirect land consumption through initiated resource flows, indirect emissions through initiated resource flows (e.g. through the production of cement and steal as construction materials) and more. Also the cultural and economic drivers and inhibitors of a systematic implementation of the urban metabolism concept need to be understood. This also concerns the awareness of different actors, including the urban inhabitants, for the footprint and impact of their resource use. These issues are critical, because their consideration enhances the overall complexity of the analysis. Nevertheless, it is necessary to assess these indirect impacts, because otherwise especially unintended and negative ecological shifts could occur.
So what? Without further development of the methodological concept of urban metabolism, it will be not possible to identify comprehensive measures enhancing urban resource efficiency, consistency and sufficiency. This is the to develop instruments and tools for actors on different scales (local, regional, national and supranational) which foster resource friendly urban areas based on the above mentioned principles of efficiency, consistency and sufficiency. The developed tools need to address indirect impacts, such as rebound effects or indirect land consumption. Further research in this issue is crucial for a sustainable development, because through these instruments and tools it becomes possible to save our common resource basis, minimize negative ecological effects, foster the local economy through an urban circular economy and guarantee a high level of urban quality of life also into the future.
Links to other fields: The urban metabolism links to a variety of different fields, e.g. resource efficiency, construction, urban planning, infrastructure design and more.