Searching for new Urban Metabolism techniques: A review towards future development for a city-scale Urban Metabolism Digital Twin

This review delves into the integration prospects of Urban Metabolism (UM) with industry 4.0 technologies, particularly digital twin (DT), to bolster sustainable urban development. Embracing a DT framework can enable the visualization of interdependencies within civil systems, facilitating the prediction of interventions to mitigate future climate change impacts. Therefore, the scope of this review was to determine how UM results are represented to end users, such as architects, and engineers and evaluate if these methods align with industry practices. Initially, we analyzed 70 UM studies to investigate the methods and visualization techniques employed. Trends revealed minimal integration of UM with Industry 4.0 technologies or DTs. The findings underscored a lack of dynamic and geographically oriented visualization in UM, with static representation methods like bar charts and Sankey diagrams prevailing, and mostly disconnected from the geographical location of the flows represented. Consequently, the research was further expanded to explicitly review the use of emerging technologies from Industry 4.0, including DTs, using targeted words. An extended review showed a gap in the integration of the UM framework with DT technologies, although an increased use in mapping was depicted. There was inconsistency in the adoption of specific technologies or visualization methods, highlighting ongoing research in this area. The increased use of geographic information system (GIS) and light detection and ranging (LiDAR) marked a pivotal change for more elaborate mapping of UM outcomes. Limited application of dynamic visualizations in UM persists, with MFA diagrams, Sankey diagrams, and bar charts being commonly used methods, despite the need to develop such type of visualizations in the sustainability field. There is an obvious lack of interoperability of these methods with Computer -Aided Design (CAD) software as well as Building Information Model (BIM) software, which are standard tools in urban planning and design. This limitation is particularly significant in environments where the ability to modify planning scenarios and work with precise spatial representations is crucial. We argue that UM can be more effective if integrated with technologies such as DT, which can resolve the spatial issue and describe UM contextualizing it and potentially depicting it in real-time. Additionally, DTs can offer promising solution by integrating UM analysis results and facilitating modifications to the 3 -dimensional environment based on this information. This capability empowers planners and designers to conduct simulations, update UM analyses, and iterate the design process, aligning with contemporary practices in planning and design. Given the interdisciplinary nature of UM, which includes various concepts such as urban flows, city flows, system of systems, and urban networks, our study deliberately focuses solely on UM and its associated frameworks. This targeted approach may limit the breadth of concepts explored, but it ensures depth and coherence in our analysis of UM for this study.