In the framework of pressing local and global environmental challenges it is essential to understand that cities are complex systems dependent on and linked to the rest of the world through global ...supply chains that embody an array of environmental flows. Cities are thus a complex articulation that intertwine local and global challenges which rely at their extended hinterland for their resource use and pollution emission. To assess the environmental sustainability of an urban area in a comprehensive manner, it is not only necessary to measure its local and direct environmental performance but also to understand and take into account its global and indirect environmental counterparts. This paper presents a comparative analysis of a territorial-based and a consumption-based approach to estimate both direct and embodied resource use and pollution flows for the case of Brussels Capital Region (Belgium). The territorial-based approach is based on local energy, water and material consumption measured data as well as measured data on waste generation and pollution emissions. The estimation of indirect resource use and pollution emissions (or consumption-based approach) is based on the regional IO-tables of the city-region of Brussels extended with multi-region input-output tables, taking into account the global flows of consumption. The comparison of these two approaches is particularly relevant in the case of cities that have limited productive activities and limited or no extraction of materials as the impact on the hinterland is often underestimated or neglected by local (environmental) policies which are only based on territorial-based figures. The results show that the indirect primary energy use, GHG emissions and material use estimated by the consumption-based approach is more than three times higher than local measures indicate. The embodied water use, estimated via IOA, was over 40 times higher than the local water consumption. These results show that territorial-based approach using local data underestimate the resource needs and pollution emissions of a city and can therefore be insufficient or even be misguiding. By mapping the origin of embodied flows it is in fact possible to illustrate the open character of an urban economy and its dependence on the global hinterland. Finally, this paper discusses the possibility and relevance to combine these two approaches to create a hybrid framework that measures the full environmental performance of cities both accurately and comprehensively.
Current levels of resource use and pollution emissions are responsible for the trespassing of most planetary boundaries. As such, operational and contextual analysis is needed to provide mitigation ...strategies and policies. This article aims to streamline Economy-Wide Material Flow Accounts (EW-MFA) at a Swiss cantonal scale, which corresponds to NUTS 3 region according to the European Statistical System. The method was developed originally to be applied at a national level. However, it can be considered as a “black-box” approach, which measures flows rather than enabling the understanding of the internal mechanisms that mobilise them. In order to overcome this challenge, the accounting was regionalized to smaller spatial units. This research developed an EW-MFA database for all 26 Swiss cantons for a time series from 2016 to 2019, including Domestic Extraction, Import, Export, and Domestic Processed Output parts. Results enable an in-depth look into Swiss material flows helping cantons to monitor their environmental pressures and develop more ambitious policies to keep their climate objectives.
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•Economy-Wide Material Flows Accounts was regionalized at Swiss canton level.•A Database including Swiss cantons material flows between 2016 and 2019 was created.•A comparative analysis was carried out between cantons to identify patterns & drivers.
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 flow's evolution caused by a city'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 Brussels’ 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.
•A dynamic, stock-driven bottom-up model is applied to the City of Melbourne, Australia.•Non-structural material replacement flows are calculated from 2018-2030 for each building.•Results show that ...the City of Melbourne required 26 kt of materials per year to maintain its current building stock.•Results show that plasterboard, carpet, timber and ceramics havethe highest average annual replacement rates.•This model supports decision-making for a more circular construction sector.
Humans are extracting and consuming unprecedented quantities of materials from the earth’s crust. The construction sector and the built environment are major drivers of this consumption which is concentrated in cities.
This paper proposes a framework to quantify, spatialise and estimate future material replacement flows to maintain urban building stocks. It uses a dynamic, stock-driven, and bottom-up model applied to the City of Melbourne, Australia to evaluate the status of its current material stock as well as estimated replacements of non-structural materials from 2018 to 2030. The model offers a high level of detail and characterises individual materials within construction assemblies for each of the 13 075 buildings modelled.
Results show that plasterboard (7 175t), carpet (7 116t), timber (6 097 t) and ceramics (3 500 t) have the highest average annual replacement rate over the studied time period. Overall, replacing non-structural materials resulted in a significant flow of 26 kt/annum, 36kg/(capita·annum) or 721t/(km2·annum). These figures were found to be compatible with official waste statistics. Results include maps depicting which material quantities are estimated to be replaced in each building, as well as an age pyramid of materials, representing the accumulation of materials in the stock, according to their service lives. The proposed model can inform decision-making for a more circular construction sector.
Cities and their building stocks result in huge environmental impacts which are critical to reduce. However, the majority of existing studies focus on operational requirements or on material stocks. ...To date, very few studies have quantified embodied environmental requirements of building stocks and spatialised them.
This study describes a bottom-up approach to spatially model building stocks and quantify their embodied environmental requirements. It uses a highly disaggregated approach where each building's geometry is modelled and used to derive a bill of quantities. Construction assemblies relevant to each building archetype (derived based on land-use, age and height) are defined using expert knowledge in construction. The initial and recurrent embodied energy, water and greenhouse gas emissions associated with each material within each assembly are calculated using a comprehensive hybrid analysis technique. This model is applied to all buildings of the City of Melbourne, Australia.
Results show that rebuilding the City of Melbourne's building stock today would require 904 kt of materials/km2 (total: 32 725 kt), 10 PJ/km2 (total: 362 PJ), 17.7 Million m3 of embodied water/km2 (total: 640.74 Million m3) and would emit 605 ktCO2e/km2 (total: 23 530 ktCO2e).
This study demonstrates the breadth of the model outputs, including material stocks maps and breakdowns of life cycle embodied requirements by material, construction assembly, building and building typology at the city level. Using such model, city councils can better manage building stocks in terms of waste processing, urban mining and circular economy, as well as reducing embodied environmental requirements over time.
•A bottom-up method to quantify and map embodied resources of cities is presented.•Material stocks, embodied energy, water and greenhouse gas emissions are quantified.•Bills of quantities are derived for each building using its geometry, type and age.•The method is applied to the City of Melbourne, Australia and its 13 075 buildings.•The method supports decision-making for more environmentally effective cities.
Within the framework of the 2015 Paris Agreement and the increased acceptance of circular economy (CE) principles of national and local governments, it is essential to study the potential effect on ...climate change of CE-strategies implemented on an urban scale. The present research quantitatively assesses the potential impact of these strategies on primary material footprint (MF) and carbon footprint (CF) of households in areas an urban area, using the case of Brussels Capital Region (BCR), Belgium. Because the CE-strategies are linked to consumption domains, this assessment first calculates both footprints of consumption domains using a city-level input-output analysis and discusses the relationship between the footprints. The findings show that the carbon footprint of BCR in 2010 was 22 Mt CO2-eq. or 20.3 t/cap. The material footprint of BCR in 2010 was 31 Mt or 29.5 t/cap. Important insights are that BCR relies on its hinterland for 98% of its primary materials and 83% of the region's greenhouse gas emissions (GHGs) are emitted outside of its territory. The household consumption domains of food, housing and transport were identified as hotspots in both footprints. Within these domains, we calculated and discussed the potential impact on both footprints of CE-strategies on consumption or production of food, mobility and housing. Results from this case show that with these strategies Brussels could mitigate 25% of its CF and 26% of its MF, 18% of its CF and 26% of its MF, and 7% of its CF and 10% of its MF, respectively. The methodology and insights could therefore support authorities and policy-makers to effectively develop coherent and consistent action plans on consumption domains to improve resource efficiency and reduce the GHGs, simultaneously.
The authors regret to inform the readers that a numerical error in the data processing has affected the reported material stock of the City of Melbourne previously disclosed in their paper.
The ...correct material intensity should read 1547 kt/km2 instead of 904 kt/km2. Figure 7 in the original manuscript should be replaced with Figure 1 which corrects the bar chart depicting the material stock.
•We conduct a bibliometric analysis of spatialization in UM.•448 publications are analyzed.•We identify five main research themes.•20 research communities are involved in the spatial debate.•A ...spatial turn in UM research seems a possible horizon.
The concept of urban metabolism has been profusely used by various disciplines over the last and current century to describe different urban phenomena. One theme that appears to gain importance in the interdisciplinary field of urban metabolism is the spatial dimension. In this article, we have carried out a bibliometric and qualitative analysis of the use of this multi-faceted notion in order to understand the place of space in urban metabolism research. Our results show that several communities within the urban metabolism field use and manipulate space for their research according to different approaches (territorial economic, socio-political, socio-ecological, governance and urban planning, and modeling). We discuss recent contributions of these communities and their approaches, their limitations, and a future agenda that might cross-fertilize them in order to embed space more consistently in urban metabolism research.
•A multiscale energy flows analysis is implemented for the case of a port-city.•Outsourcing is analyzed through dependency and indirect flows indicators.•The local scale represents about 0.05% of the ...inputs and 6% of the indirect flows.•Most energy losses are domestic while most embodied energy is foreign.•Dependency will not disappear with energy transition but merely changes scale.•Reducing embodied energy and energy losses may imply trade-offs across spatial scales.
Outsourcing of urban metabolisms is a phenomenon that has grown exponentially over the last century. It is a cause of vulnerability for cities for two main reasons. They are dependent on distant hinterlands and their consumption induces global environmental impact they do not fully control. This study aims to investigate these two effects of outsourcing through a single, multiscale approach to energy accounting. A spatially differentiated energy flow analysis (EFA) is developed, which includes indicators for dependency, embodied energy and energy losses. Applied to the case of the harbor-industrial area of Saint-Nazaire, France, the results show that the global scale dominates dependency and embodied energy indicators, whereas primary energy losses occur mainly at the domestic scale. The local scale accounts for less than 0.1% of the energy supply and about 6% of indirect flows. The spatial trajectories of some renewables (wood, biofuels, wind electricity) suggest that the energy transition could decrease global dependency, but with a transfer to the domestic level, and not necessarily to the local scale, without a radical change from the port's production system. Moreover, trade-offs could emerge between reducing the amount of embodied energy in foreign countries and using energy losses as a local secondary source, depending on the resource used to generate the losses. This study highlights thus the need to link local transition policies more closely to outsourcing issues in order to allow a comprehensive understanding of the possible transfers in terms of dependency and environmental burdens that may occur in a transition context.
Hosting more than half of the world population, cities are currently responsible for two thirds of the global energy use and three quarters of the global CO2 emissions related to energy use. As ...humanity becomes more urbanized, urban systems are becoming a major nexus of global sustainability. Various studies have tried to pinpoint urban energy use drivers in order to find actionable levers to mitigate consumption and its associated environmental effects. Some of the approaches, mainly coming from complexity science and industrial ecology disciplines, use city-scale data to find power-laws relating to different types of energy use metrics with urban features at a city-scale. By doing so, cities’ internal complexity and heterogeneity are not explicitly addressed. Moreover, to our knowledge, no studies have yet explicitly addressed the potential scale dependency of such drivers. Drivers might not be transferable to other scales and yield undesired effects. In the present study, power-law relations are examined for 10 cities worldwide at city scale and infra-city scale, and the results are compared across scales. Relations are made across three urban features for three energy use intensity metrics. The results show that energy use drivers are in fact scale-dependent and are city-dependent for intra-urban territories.
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