Towards a Dynamic Approach to Urban Metabolism
Summary
Urban metabolism (UM) is a way of characterizing the flows of materials and energy through and within cities. It is based on a comparison of cities to living organisms, which, like cities, require energy and matter flows to function and which generate waste during the mobilization of matter. Over the last 40 years, this approach has been applied in numerous case studies. Because of the data-intensive nature of a UM study, however, this methodology still faces some challenges. One such challenge is that most UM studies only present macroscopic results on either energy, water, or material flows at a particular point in time. This snapshot of a particular flow does not allow the tracing back of the flowrsquo;s evolution caused by a cityrsquo;s temporal dynamics. To better understand the temporal dynamics of a UM, this article first presents the UM for Brussels Capital Region for 2010, including energy, water, material, and pollution flows. A temporal evaluation of these metabolic flows, as well as some urban characteristics starting from the seminal study of Duvigneaud and Denayer-De Smet in the early 1970s to 2010, is then carried out. This evolution shows that Brussels electricity, natural gas, and water use increased by 160%, 400%, and 15%, respectively, over a period of 40 years, whereas population only increased by 1%. The effect of some urban characteristics on the UM is then briefly explored. Finally, this article succinctly compares the evolution of Brusselsrsquo; UM with those of Paris, Vienna, Barcelona, and Hong Kong and concludes by describing further research pathways that enable a better understanding of the complex functioniong of UM over time.
Introduction
In a context of evident and pressing environmental concerns, ranging from natural resource depletion (Prior et al. 2012) to the alteration and the permanent damage of natural ecosystems (Corvalan et al. 2005), the mitigation of natural resource use and of their respective environmental impacts is of the highest importance. Although covering only 2% of the Earthrsquo;s land surface (Balk et al. 2005), cities now host more than 50% of the global population and are estimated to account for 71% to 76% of carbon dioxide (CO2) emissions from energy use and between 67% and 76% of global energy use (Seto et al. 2014). In fact, cities can be seen as concentration nodes of resource consumption that mobilize material and energy flows from around the world in order to match its inhabitantsrsquo; consumption needs and its production needs. In this mobilization of matter and energy, resources are extracted, processed, transformed, and are discarded after their consumption. All these activities have local as well as global economic, social, and environmental consequences given that, very often, all of these actions occuroutside of the city boundaries (Tukker et al. 2014; Wiedmannet al. 2015).
Considering that global urban population is likely to continue to increase, especially in developing countries (UN 2014), it can be assumed that cities will continue to be created and expanded to host this additional population and therefore create ever-increasing environmental pressures. In order to assess, forecast, and coherently reduce the present and future global enviromental impacts of urban resource consumption, it is essential to better understand how cities or urban systems consume resources over time and what the underlying drivers are (Baynes and Bai 2012).Whereas an environmental assessment provides a snapshot of the environmental state of a city, tracing its temporal evolution creates a dynamic view—a movie—about the changes in its use of resources and emission of pollution flows. In fact, it is only with this movie that we can be informed about the ever-changing reciprocal relationship between a dynamic urban system composed of socioeconomic, political, and physical built environment parts, on the one hand, and its resource use and environmental effect on the other hand.
To do so, it is first necessary to assess resource use and pollution emissions using a comprehensive methodology that can take into account most physical flows entering and exiting the urban area. Within the field of urban environmental assessment, Baynes and Wiedmann (2012) identified two main approaches, namely, the production- or metabolism-based approach and the consumption or input-output–based approach. The metabolism-based approach takes into account all imports and emissions directly occurring inside the city territory regardless of whether this consumption is serving local inhabitantsrsquo; needs or foreign needs through the manufacturing and exporting of goods and services (Minx et al. 2011). This is often based on the collection of local statistics and data from a number of administrations (Barles 2009). The consumption-based approach combines national and multiregional input-output (MRIO) tables with national expenditure data (Wiedmann 2009) in order to measure direct and indirect (or embodied) resource use and environmental impacts of local consumption (Lenzen et al. 2004). However, the required data to carry out the latter approach are usually only available at a national scale, which do not necessarily reflect the specific urban situation. In addition, MRIO tables are quite recent and are not available before 1990, which makes it difficult to trace a long-term evolution of resource use (Dietzenbacher et al. 2013; Lenzen et al. 2013).
Consequently, this article proposes applying a production or urban metabolism (UM)-based approach to comprehensively assess the resource use and pollution emissions of Brussels Capital Region (BCR) over 40 years. The contribution of this study is fourfold. First, to update the results of the seminal study on Brusselsrsquo;ecosystem (Duvigneaud and Denayer-De Smet 1977), which are still used, are some cases for comparison wit
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Towards a Dynamic Approach to Urban Metabolism
Urban metabolism (UM) is a way of characterizing the flows of materials and energy through and within cities. It is based on a comparison of cities to living organisms, which, like cities, require energy and matter flows to function and which generate waste during the mobilization of matter. Over the last 40 years, this approach has been applied in numerous case studies. Because of the data-intensive nature of a UM study, however, this methodology still faces some challenges. One such challenge is that most UM studies only present macroscopic results on either energy, water, or material flows at a particular point in time. This snapshot of a particular flow does not allow the tracing back of the flowrsquo;s evolution caused by a cityrsquo;s temporal dynamics. To better understand the temporal dynamics of a UM, this article first presents the UM for Brussels Capital Region for 2010, including energy, water, material, and pollution flows. A temporal evaluation of these metabolic flows, as well as some urban characteristics starting from the seminal study of Duvigneaud and Denayer-De Smet in the early 1970s to 2010, is then carried out. This evolution shows that Brussels electricity, natural gas, and water use increased by 160%, 400%, and 15%, respectively, over a period of 40 years, whereas population only increased by 1%. The effect of some urban characteristics on the UM is then briefly explored. Finally, this article succinctly compares the evolution of Brusselsrsquo; UM with those of Paris, Vienna, Barcelona, and Hong Kong and concludes by describing further research pathways that enable a better understanding of the complex functioniong of UM over time.
Introduction
In a context of evident and pressing environmental concerns, ranging from natural resource depletion (Prior et al. 2012) to the alteration and the permanent damage of natural ecosystems (Corvalan et al. 2005), the mitigation of natural resource use and of their respective environmental impacts is of the highest importance. Although covering only 2% of the Earthrsquo;s land surface (Balk et al. 2005), cities now host more than 50% of the global population and are estimated to account for 71% to 76% of carbon dioxide (CO2) emissions from energy use and between 67% and 76% of global energy use (Seto et al. 2014). In fact, cities can be seen as concentration nodes of resource consumption that mobilize material and energy flows from around the world in order to match its inhabitantsrsquo; consumption needs and its production needs. In this mobilization of matter and energy, resources are extracted, processed, transformed, and are discarded after their consumption. All these activities have local as well as global economic, social, and environmental consequences given that, very often, all of these actions occuroutside of the city boundaries (Tukker et al. 2014; Wiedmannet al. 2015).
Considering that global urban population is likely to continue to increase, especially in developing countries (UN 2014), it can be assumed that cities will continue to be created and expanded to host this additional population and therefore create ever-increasing environmental pressures. In order to assess, forecast, and coherently reduce the present and future global enviromental impacts of urban resource consumption, it is essential to better understand how cities or urban systems consume resources over time and what the underlying drivers are (Baynes and Bai 2012).Whereas an environmental assessment provides a snapshot of the environmental state of a city, tracing its temporal evolution creates a dynamic view—a movie—about the changes in its use of resources and emission of pollution flows. In fact, it is only with this movie that we can be informed about the ever-changing reciprocal relationship between a dynamic urban system composed of socioeconomic, political, and physical built environment parts, on the one hand, and its resource use and environmental effect on the other hand.
To do so, it is first necessary to assess resource use and pollution emissions using a comprehensive methodology that can take into account most physical flows entering and exiting the urban area. Within the field of urban environmental assessment, Baynes and Wiedmann (2012) identified two main approaches, namely, the production- or metabolism-based approach and the consumption or input-output–based approach. The metabolism-based approach takes into account all imports and emissions directly occurring inside the city territory regardless of whether this consumption is serving local inhabitantsrsquo; needs or foreign needs through the manufacturing and exporting of goods and services (Minx et al. 2011). This is often based on the collection of local statistics and data from a number of administrations (Barles 2009). The consumption-based approach combines national and multiregional input-output (MRIO) tables with national expenditure data (Wiedmann 2009) in order to measure direct and indirect (or embodied) resource use and environmental impacts of local consumption (Lenzen et al. 2004). However, the required data to carry out the latter approach are usually only available at a national scale, which do not necessarily reflect the specific urban situation. In addition, MRIO tables are quite recent and are not available before 1990, which makes it difficult to trace a long-term evolution of resource use (Dietzenbacher et al. 2013; Lenzen et al. 2013).
Consequently, this article proposes applying a production or urban metabolism (UM)-based approach to comprehensively assess the resource use and pollution emissions of Brussels Capital Region (BCR) over 40 years. The contribution of this study is fourfold. First, to update the results of the seminal study on Brusselsrsquo;ecosystem (Duvigneaud and Denayer-De Smet 1977), which are still used, are some cases for comparison with other case studies because of the lack of more
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