Reducing scale-mismatch in urban studies with a common definition of urban typologies and system boundary

Sustainable urban planning requires a better understanding of social, ecological, technological, and political patterns, processes, and their feedbacks affecting urban dynamics. These different processes and their mutual interactions occur at different spatio-temporal scales. However, different disciplinary approaches (e.g. urban ecology, urban metabolism) focus only on some of them and on specific scales, and this could create mismatches by missing interactions and feedbacks occurring in spatial scales and time-frames not included in the system boundary. In addition, planning and governance usually takes into account short time frames and administrative spatial limits, which in many cases do not match the scale of the processes. Defining common urban typologies and system boundaries relevant for urban metabolism and urban ecology processes appears a necessary step to reduce scale-mismatches in urban studies in order to i) facilitate the transfer of knowledge ii) develop integrated urban ecology and urban metabolism assessments, iii) and better fit the temporal scales of governance and planning. This paper proposes a methodological procedure to establish shared urban typologies and system boundaries for integrated studies, defining an initial list of common descriptive indicators for European urban areas. A critical review of scientific literature supported the identification of descriptive indicators, time-frames, and methodological procedures for defining urban typologies and system boundaries. The list of indicators was reduced to a core set of indicators relevant for urban metabolism and urban ecology processes and time-frames of interest. A methodological procedure for the establishment of urban system boundaries was developed by modifying the OECD approach to define cities. For urban typologies, three spatial levels were defined: urban region, metropolis/city, and neighbourhood, and the adequacy of the indicators for them investigated. For each level, the typologies were defined considering urban resource consumption types and ecological functioning types. The methodological procedure was applied to one EU-pilot city to investigate areas of improvement and feasibility for urban planning practice. Two types of urban system boundaries (‘foreground’ and ‘background’) are defined. This permits better consideration of the exchange of matter and ecological flows and the environmental burden shifting between city/metropolisforeground system) and their urban regions (background system). Population density, building density, percentage of sealing surfaces, and administrative areas are identified as relevant indicators for the foreground system. While density of infrastructure networks, commuting population, and land cover types are considered key for background systems. Regarding urban typologies, the characterisation of urban sub-system patterns (e.g. building domain, green open spaces) is perceived as key for defining urban typologies at neighbourhood and city/metropolis levels. This is because spatial metrics are crucial to measure porosity, compactness, and heterogeneity. For the urban region level, environmental indicators (e.g. temperature, land cover) are considered highly relevant. This initial framework might permit to advance towards the definition of common system boundaries and urban typologies for integrated urban metabolism and urban ecology studies. The material-energy flows and ecological processes characterisation of multi-level urban types, and their changes over time, may allow tailoring sustainability strategies to specific types and their iterative adaptation.