Quantification of urban metabolism through coupling with the life cycle assessment framework: concept development and case study

TLDR

Cities consume resources and generate waste disproportionate to their populations, and urban metabolism offers a way to quantify annual material and energy inputs and emissions from a city’s infrastructure. The study aims to quantify and benchmark urban environmental impacts by integrating urban metabolism with life cycle assessment, enabling modeling of upstream and downstream pressures and introducing advanced indicators. The authors developed a UM–LCA model that couples urban metabolism with life cycle assessment to capture upstream and downstream pressures and provide a suite of advanced indicators. Applied to five global cities, the UM–LCA model improved mass and energy flow quantification over earlier UM methods, identified dominant sources of environmental footprints, and revealed that wealthier cities’ footprints are driven by personal consumption while poorer cities are more affected by local burdens from outdated infrastructure.

Abstract

Cities now consume resources and produce waste in amounts that are incommensurate with the populations they contain. Quantifying and benchmarking the environmental impacts of cities is essential if urbanization of the world’s growing population is to occur sustainably. Urban metabolism (UM) is a promising assessment form in that it provides the annual sum material and energy inputs, and the resultant emissions of the emergent infrastructural needs of a city’s sociotechnical subsystems. By fusing UM and life cycle assessment (UM–LCA) this study advances the ability to quantify environmental impacts of cities by modeling pressures embedded in the flows upstream (entering) and downstream (leaving) of the actual urban systems studied, and by introducing an advanced suite of indicators. Applied to five global cities, the developed UM–LCA model provided enhanced quantification of mass and energy flows through cities over earlier UM methods. The hybrid model approach also enabled the dominant sources of a city’s different environmental footprints to be identified, making UM–LCA a novel and potentially powerful tool for policy makers in developing and monitoring urban development policies. Combining outputs with socioeconomic data hinted at how these forces influenced the footprints of the case cities, with wealthier ones more associated with personal consumption related impacts and poorer ones more affected by local burdens from archaic infrastructure.