An expanded urban metabolism method: Toward a systems approach for assessing urban energy processes and causes

The integrated study of energy and urban systems has recently become a critical component of sustainability research and policy. Increasing urbanization of human societies combined with intense energy demands of modern economies have driven a recognition that sustainable practices require a systems approach to both the study and application of sustainability principles. Urban metabolism has emerged as a leading methodology for quantifying energy consumption and use patterns in urban environments. Though typically applied as a method of accounting for total energy and materials inputs and outputs into cities, its interdisciplinary history and methods allow urban metabolism to be expanded in ways that will allow more comprehensive and integrated assessment of the patterns and processes of urban energy systems. In this article, we review the concept of urban metabolism—including its two typical approaches: mass balance and “emergy” methods—and offer a means to expand urban metabolism into a platform that incorporates socioeconomic analysis, policy analysis, and additional quantitative methodologies (such as life cycle assessment). This expanded urban metabolism framework is more comprehensive analytically and builds upon the documented capacity of traditional urban metabolism to account for total energy and materials flows of cities to provide an integrated platform for analysis of both energy patterns and the causal processes that govern energy in contemporary cities.