The Environmental Footprint of Cities: Insights in the Steps forward to a New Methodological Approach

Cities are complex entities which are constantly evolving, they are responsible for the largest share of most environmental impacts, but provide also major opportunities for improvement. Nevertheless, holistic methodologies to evaluate the environmental footprint of cities are still lacking at the urban scale level. Currently, carbon footprint and water footprint are the most used methods to evaluate the environmental performance of cities, despite their limited scope. The Urban Metabolism (UM) concept allowsmaking an inventory of the flows into and out of the city, but it does not allow to interpret these flows in terms of environmental impacts. Life cycle assessment (LCA) provides this capability, but it is not yet feasible at urban scale. A first attempt to fuse the two approaches was made, but this proposal considers only four environmental indicators.It is clear that none of these methods can represent the whole environmental picture. Providing a new methodology adapt to urban context and extending the list of environmental impact categories is of paramount relevance to move towards a comprehensive and reliable environmental assessment able to guide cities on a sustainable transition path.For this reason, the main aims of this contribution are to give a comprehensive and critical insight in the most valuable and current available methods and tools able to assess the environmental burdens of cities, and at the same time trace the steps forward to propose a new methodology that could be capable to overcome the current gaps. This paper presents the first part of a broader research project which aims at developing a hybrid top-down and bottom-up approach to identify the contribution of the main flows at the macro-scale level, but also the main hotspots on the micro-scale level and the potential improvements.