ABSTRACT
Post-industrial cities are characterized by their routine use of energy as a driving force to power production, transportation of goods, construction of buildings and infrastructure as well as domestic comfort. The existence and maintenance of a city and its internal structure depend on the flow of goods and services into, out of, and throughout that city. The materials, energy, and food supplies brought into cities; the transformation of these inputs within the cities; and the products and wastes sent out from the cities are often referred to as urban metabolism, a concept first suggested by Wolman (1965). Metabolism is a concept adopted from biology, which refers to the physiological processes within a living organism that describes the energy flow connected to the conversion of matter for reproduction. Extending this concept to the social sciences, metabolism can be seen as a main feature in the analysis of human interactions with the natural environment. Like human metabolism, the physical and biological processes of a city system transform inflows of energy and materials into useful products, services, and wastes. The complete metabolism of a city consists of many inputs such as food, fuel, clothing, durable goods, electricity, construction materials, and services (Figure 40.1). The linear metabolic system of the modern city is different from nature’s circular metabolism, where every output by an organism is also an input that renews and sustains the living environment. The metabolic cycle is not completed until the residues of daily consumption have been removed and disposed of adequately with minimum nuisance and hazard to life. Kennedy et al. (2007) reviewed eight urban metabolism studies conducted since 1965 and identified metabolic processes that threaten the sustainability of cities. The major environmental problems and associated social costs of an urban ecosystem are related to the rapid increase of resource inputs for urban consumption and the disposal of construction waste, both of which are nuisances to urban dwellers. Much more radical changes in the urban metabolism are required to make cities more ecologically viable.
