Summary Data from urban metabolism studies from eight metropolitan regions across five continents, conducted in various years since 1965, are assembled in consistent units and compared. Together with studies of water, materials, energy, and nutrient flows from additional cities, the comparison provides insights into the changing metabolism of cities. Most cities studied exhibit increasing per capita metabolism with respect to water, wastewater, energy, and materials, although one city showed increasing efficiency for energy and water over the 1990s. Changes in solid waste streams and air pollutant emissions are mixed. The review also identifies metabolic processes that threaten the sustainability of cities. These include altered ground water levels, exhaustion of local materials, accumulation of toxic materials, summer heat islands, and irregular accumulation of nutrients. Beyond concerns over the sheer magnitudes of resource flows into cities, an understanding of these accumulation or storage processes in the urban metabolism is critical. Growth, which is inherently part of metabolism, causes changes in water stored in urban aquifers, materials in the building stock, heat stored in the urban canopy layer, and potentially useful nutrients in urban waste dumps. Practical reasons exist for understanding urban metabolism. The vitality of cities depends on spatial relationships with surrounding hinterlands and global resource webs. Increasing metabolism implies greater loss of farmland, forests, and species diversity; plus more traffic and more pollution. Urban policy makers should consider to what extent their nearest resources are close to exhaustion and, if necessary, appropriate strategies to slow exploitation. It is apparent from this review that metabolism data have been established for only a few cities worldwide, and interpretation issues exist due to lack of common conventions. Further urban metabolism studies are required.

The Changing Metabolism of Cities

http://www.igbp.net/download/18.5831d9ad13275d51c098000258/1376382967821/Kennedy_et_al_2010_UM_urbanplanning_design.pdf

The study of urban metabolism and its applications to urban planning and design.

The world’s population is now over 50% urban, and cities make an important contribution to national greenhouse gas (GHG) emissions. Many cities are developing strategies to reduce their emissions. Here we ask how and why emissions differ between cities. Our study of ten global cities shows how a balance of geophysical factors (climate, access to resources, and gateway status) and technical factors (power generation, urban design, and waste processing) determine the GHGs attributable to cities. Within the overall trends, however, there are differences between cities with more or less public transit; while personal income also impacts heating and industrial fuel use. By including upstream emissions from fuels, GHG emissions attributable to cities exceed those from direct end use by up to 25%. Our findings should help foster intercity learning on reducing GHG emissions.

https://pubs.acs.org/doi/pdf/10.1021/es200849z

Greenhouse Gas Emissions from Global Cities

Methodology for inventorying greenhouse gas emissions from global cities

Approximately 75–80% of the population of North America currently lives in urban areas as defined by national census bureaus, and urbanization is continuing to increase. Future trajectories of fossil fuel emissions are associated with a high degree of uncertainty; however, if the activities of urban residents and the rate of urban land conversion can be captured in urban systems models, plausible emissions scenarios from major cities may be generated. Integrated land use and transportation models that simulate energy use and traffic-related emissions are already in place in many North American cities. To these can be added a growing dataset of carbon gains and losses in vegetation and soils following urbanization, and a number of methods of validating urban carbon balance modeling, including top down atmospheric monitoring and urban ‘metabolic’ studies of whole ecosystem mass and energy flow. Here, we review the state of our understanding of urban areas as whole ecosystems with regard to carbon balance, including both drivers of fossil fuel emissions and carbon cycling in urban plants and soils. Interdisciplinary, whole-ecosystem studies of the socioeconomic and biophysical factors that influence urban carbon cycles in a range of cities may greatly contribute to improving scenarios of future carbon balance at both continental and global scales.

/pdf/urban-ecosystems-and-the-north-american-carbon-cycle-2afw8wmcgs.pdf

Urban ecosystems and the North American carbon cycle

Research in the area of sustainable urban infrastructure reflects the need to design and manage engineering systems in light of both environmental and socioeconomic considerations. A principal chal...

/pdf/developing-sustainability-criteria-for-urban-infrastructure-1a3teow8fd.pdf

Developing sustainability criteria for urban infrastructure systems

An urban metabolism analysis is a means of quantifying the overall fluxes of energy, water, material, and wastes into and out of an urban region. Analysis of urban metabolism can provide important ...

Estimating the urban metabolism of Canadian cities: Greater Toronto Area case study

A systems approach is used to model the urban water cycle. A model for analyzing the flows of water, energy, and chemicals and associated greenhouse gas emissions through the urban water infrastructure system is developed. A model is constructed to represent the City of Toronto urban water system from 2001 up to the year 2010. Scenarios are developed to assess the system-wide impacts of water distribution pipe renewal, sewer relining, demand management strategies, and energy recovery from anaerobically digested wastewater biosolids. Initiatives targeted at the early stages of the urban water cycle have greater positive downstream impacts on selected environmental indicators. Specifically, strategies aimed at reducing water demand produce more significant system-wide benefits. Demand management strategies aimed at reducing demand by 15% result in savings on the order of 12 — 18% for all environmental indicators. Demand management is also one of the most cost effective options.

Halla R Sahely

Papers

Developing sustainability criteria for urban infrastructure systems

Estimating the urban metabolism of Canadian cities: Greater Toronto Area case study

Water Use Model for Quantifying Environmental and Economic Sustainability Indicators