Review The study of urban metabolism and its applications to urban planning and design C. Kennedy a, * , S. Pincetl b , P. Bunje b a Department of Civil Engineering, University of Toronto, Toronto, Canada b Institute of the Environment, UCLA, CA, United States The presents a chronological review of urban metabolism studies and highlights four areas of application. article info Article history: Received 12 October 2010 Accepted 15 October 2010 Keywords: Cities Energy Materials Waste Urban planning Urban design Greenhouse gas emissions Sustainability indicators abstract Following formative work in the 1970s, disappearance in the 1980s, and reemergence in the 1990s, a chronological review shows that the past decade has witnessed increasing interest in the study of urban metabolism. The review finds that there are two related, non-conflicting, schools of urban metabolism: one following Odum describes metabolism in terms of energy equivalents; while the second more broadly expresses a city’s flows of water, materials and nutrients in terms of mass fluxes. Four example applications of urban metabolism studies are discussed: urban sustainability indicators; inputs to urban greenhouse gas emissions calculation; mathematical models of urban metabolism for policy analysis; and as a basis for sustainable urban design. Future directions include fuller integration of social, health and economic indicators into the urban metabolism framework, while tackling the great sustainability challenge of reconstructing cities. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The concept of the urban metabolism, conceived by Wolman (1965), is fundamental to developing sustainable cities and communities. Urban metabolism may be defined as “the sum total of the technical and socio-economic processes that occur in cities, resulting in growth, production of energy, and elimination of waste” (Kennedy et al., 2007). In practice, the study of an urban metabo- lism involves ‘big picture’ quantification of the inputs, outputs and storage of energy, water, nutrients, materials and wastes for an urban region. While research on urban metabolism has waxed and waned over the past 45 years, in the last decade it has accelerated. Moreover, as this review will show, practical applications of urban metabolism are emerging. The notion of urban metabolism is loosely based on an analogy with the metabolism of organisms, although in other respects parallels can also be made between cities and ecosystems. Cities are similar to organisms in that they consume resources from their surroundings and excrete wastes. “Cities transform raw materials, fuel, and water into the built environment, human biomass and waste” (Decker et al., 2000). Of course, cities are more complex than single organisms e and are themselves home to multitude of organisms e humans, animals and vegetation. Thus, the notion that cities are like ecosystems is also appropriate. Indeed, the model of a natural ecosystem is in some respects the objective for developing sustainable cities. Natural ecosystems are generally energy self- sufficient, or are subsidized by sustainable inputs, and often approximately conserve mass, through recycling by detrivores. Were cities to have such traits, they would be far more sustainable. Contemporary cities, however, have large linear metabolism with high through flows of energy and materials. The first purpose of this paper is to review the development of the urban metabolism concept largely through academic research literature. The chronological review shows that after a few forma- tive studies in the 1970s, interest in urban metabolism almost disappeared in the 1980s. Then after slowly reemerging in the 1990s, study of urban metabolism has grown in the past 10 years, with over 30 papers produced. The review also describes how two related, non-conflicting, schools of study have developed. One, primarily based on the work of Odum, aims to describe urban metabolism in terms of energy equivalents. The other takes a broader approach, expressing a city’s flows of water, materials and nutrients in terms of mass fluxes. The second purpose of this paper is to ask: What use are urban metabolism studies for urban planning and design? Most studies of urban metabolism have primarily been accounting exercises. These are useful in that they provide indicators of urban sustainability, and the measures of energy consumption, material flows and * Corresponding author. E-mail address: christopher.kennedy@utoronto.ca (C. Kennedy). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2010.10.022 Environmental Pollution xxx (2010) 1e9 Please cite this article in press as: Kennedy, C., et al., The study of urban metabolism and its applications to urban planning and design, Environmental Pollution (2010), doi:10.1016/j.envpol.2010.10.022