Analyzing a city's metabolism

Collection of urban metabolism (UM) data is required for assessing the sustainability of cities. A UM study involves quantification of the inflows, outflows, storage and production of energy and materials within an urban boundary. Such data can serve a variety of purposes, whether as input to city greenhouse gas (GHG) inventorying, for determination of urban ecological footprints, or sustainability assessment in specific areas such as water use, air pollution, waste, materials management and so on. About 20 relatively comprehensive UM studies have been published in academic literature (Kennedy et al. 2011). The World Bank has also conducted several studies of cities (Hoornweg et al. 2012), and many more cities are collecting data on some aspects of UM as part of GHG inventorying. The objective of this chapter is to provide practical guidance for undertaking a UM study. In particular this will involve description of data collection techniques and estimation methods, and potential pitfalls to avoid in determining various components of UM. For example, it will describe how transportation fuel consumption can be determined from vehicle counts, sales data and/or transportation models; and how material stocks can be scaled up from studies of individual buildings/infrastructure segments. It is very much a ‘how to do it’ guide for both city managers and academics. Figure 13.1 provides a generic framework for assessing the UM, broadly including inflows, outflows, internal flows, storage and production of biomass, energy, minerals and water.