The population equivalent as a novel approach for life cycle assessment of cities and inter-city comparisons

摘要

Purpose Since the Agenda 2030 for Sustainable Development was set, cities are gaining momentum in the sustainability debate as favorable hubs of interventions to implement environmentally friendly policies. What makes a city sustainable is still object of debate though, as standards, frameworks, and methodologies with different goals and scope proliferate. Life cycle assessment (LCA) is promising in supporting cities to achieve this ambitious task, but methodological constraints still exist to make it applicable at city scale. This study offers proposals to solve current bottlenecks in the goal and scope phase for the application of LCA to urban systems and allowing for a meaningful inter-city comparison and benchmarking. Methods In order to define cities along with their function(s) and functional unit, a systematic desk study combined with authors' knowledge is performed and tested on the city of Leuven (Belgium). The final outcome includes the following: (i) categorization of cities based on their (prevalent) function(s); (ii) sets of indicators able to support both urban policies and LCA studies; and (iii) accounting and use of the population equivalent concept, as innovative and enhanced functional unit able to summarize and normalize different entities (i.e., residents and other city-users) to one single metric. Results and discussion Despite the fervent debate about cities and their sustainability, few studies address the topic of categorization and benchmarking of cities in an exhaustive way. The proposals were successfully applied to the city of Leuven, as first case study, with different degrees of extent and quality. A shortlist of five biophysical and economic criteria combined with ten urban categories represents a first straightforward tier of categorization. The population equivalent has the triple function of being descriptive, quantitative, and analytical for performing thorough urban sustainability studies and define targeted policies, but requires high computational and data collection efforts. The quality and granularity of collected information proved to be directly proportional to the access of local data sources, and inversely to its complexity, i.e., sufficient for policy support, but improvable when the goal is to perform LCA studies. Conclusions The functional categorization of cities and the calculation of the population equivalent provide a new approach for meaningful and helpful inter-city comparisons, as well as an enhanced detection and interpretation of urban environmental burdens. Due to the relevance of the topic in the scientific debate, the authors envisage complementary and multidisciplinary studies to make cities more and more part of the solution to the sustainability challenge, especially to improve the concept of population equivalent and the data management.