Consumption based footprint of a city

Since a few years, there is a growing interest for consumption based indicators reflecting the environmental impacts generated by citizen final demand. Considering the complexity and the variety of environmental and intermediate flows in an urban territory, constructing life cycle inventory with classical bottom up approaches for data collection is not a pragmatic option for LCA practitioners. This study focuses on a consistent combination of local emission and activity data with Environmentally Extended Input Output Analysis (EEIOA), into a hybrid EEIO-LCA to assess the environmental impacts generated by the final demand of a city. A hybrid EEIO-LCA has been carried out to capture the footprint generated by a French city. To integrate the city specificities, regional input-output table is estimated from French input output table, using location quotients derived from local employment data. The obtained Leontief matrix is coupled with national environmental extensions and foreign trade data. This approach provides a comprehensive supplement to local sparse environmental data, mainly available for energy use and road transport. The priority was given to local available data and special care was taken to avoid double counting. This inventory is then aggregated into a combined footprint approach (carbon, water, biodiversity and resources) to reflect the environmental impacts generated by citizen’s consumption. As expected for a high density population territory, where consumed goods and services are broadly imported, indirect impacts represent a major contribution to the footprint of the city. The results suggest environmental footprint is highly sensitive to consumer choices and expenses allocations. The approach provides a promising solution to couple top down information with local available data, in order to get a full picture of the environmental pressures generated by a large city. Regionalizing economic tables enable to capture the specificities of local domestic businesses. A natural continuation would be to regionalize final demand with local expenses allocation features. The approach could be used as a screening assessment tool for decision makers, to target potential hotspots of improvement, in a sustainable perspective. The study also illustrates some lack of data availability to comprehensively account for the city impacts and could guide data collection, both from a local and a national level.

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