Comparing a territorial-based and a consumption-based approach to assess the local and global environmental performance of cities

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.

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