Narrowing cycles but where? Geospatial material and building stocks in IAMs to inform reduce and reuse pathways

Building construction and use are major drivers of climate change. To avoid these impacts, research is exploring the potential of narrowing material and energy cycles (“narrow” strategies) by reducing floor area per capita. Yet, integrated assessment models (IAM) have mostly overlooked material stocks and flow, service levels, and geospatial location of buildings. Thus, they have only limited capacity in modelling such floor area dynamics which are dependent on urbanization trends and changes in dwelling preferences. Current modelling of narrow strategies in IAMs, where available, is therefore focused on normative targets of overall reduction in floor area per capita without consideration of local building stock limitations. Inspired by recent advances in urban metabolism studies of representing urban form in material and energy flow modelling, we propose an integration of detailed geospatial building and material stock accounts with IAMs. Specifically, we demonstrate how the open-source building stock database EUBUCCO can inform the modelling of narrow strategies in the building sector model MESSAGEix-Buildings by adding subnational detail and urban density parameters. EUBUCCO is the first near-complete 3D model of individual buildings including building footprints, heights, usage types and material content in Europe. The database is a collection of government, volunteered, and satellite-derived data, and missing attribute values are inferred with machine learning. Material content is based on the globally harmonized material intensity database RASMI. MESSAGEix-Buildings is a framework to model the material stocks and flows and energy demand of buildings at national or larger scales in future scenarios. Embedding material flow analysis for stock turnover accounting and energy demand modelling at sectoral level, the framework is soft-linked to the MESSAGEix-GLOBIOM IAM to account for demand and supply sides interactions and greenhouse gas (GHG) emissions under different climate policies. EUBUCCO is integrated in MESSAGEix-Buildings by differentiating building and material stocks, as well as demographic trends and climate, at NUTS2 level and degree of urbanicity. This enables for improved representation of floor area and urban form-related aspects, and their regional distributions. With this geospatially informed IAM module, we can model the effect of regionally differentiated floor area reduction pathways, consider population-trend-dependent urban mining potentials, and effects of reverse urbanization such as revitalization of rural building stocks. Ultimately, this integrated module can inform prioritization of such reuse and reduce strategies for climate change mitigation in the housing sector.