Urban Metabolism

The concept of urban metabolism provides a framework for examining natural resource flows and use in urban areas. Urban metabolism studies draw an analogy with the metabolic requirements and processes of an organism. Like an organism, a city requires water, energy, food, and other resources to fuel, grow, and reproduce itself. It also produces wastes and residuals that must be disposed of with minimal hazard. Urban metabolism studies can be used to provide insight into the sustainability of the relationships between a city and its supporting physical environments and have recently begun to include social and economic relationships as well.

The first formal urban metabolism study was prepared in 1965 by Abel Wolman for a hypothetical North American city of 1 million inhabitants to highlight key urban environmental issues of modern industrialized cities: the [Page 2964]provision of a safe and adequate urban water supply, the effective disposal of sewage, and the control of air pollution. Since then, approximately 10 urban metabolism studies of actual cities have been conducted, including Hong Kong, Vienna, Toronto, Tokyo, London, and Sydney. Analysis using urban metabolism as a framework metaphor typically takes the form of a material flow analysis, where researchers take stock of the inputs, storage, transformation, and output of different materials and their residuals across a defined urban system and over time. While some studies look specifically at the flow of a single material such as water or nitrogen, most provide a comprehensive accounting of inputs and wastes.

Table 1 Urban metabolism of Hong Kong, 1971 and 1997

Sources: Data compiled from Newcombe, K., Kalma, J. D., & Aston, A. R. (1978). The metabolism of a city: The case of Hong Kong. Atnbio, 7, 3–15; Warren-Rhodes, K., & Koenig, A. (2001). Escalating trends in the urban metabolism of Hong Kong: 1971–1997. Atnbio, 30, 429–438.

Taking stock of material flows across an urban system and over time helps draw attention to the need to examine the systemwide impacts of the consumption of natural resources and provides valuable information for decision making and planning for the future of cities. An urban metabolism study may reveal inefficiencies in resource use, opportunities for policy intervention to slow or prevent the exhaustion of resource supplies, and the sources of potential problems from the buildup of potentially hazardous materials and emissions within the urban system and its surrounding environment.