How regional spatial planning shapes suburban heat stress: Scenario-based PALM simulations around Graz, Austria

Urban climate is shaped not only by processes within city centres but also by land-use changes and development dynamics in surrounding suburban areas. High-resolution urban climate models such as the PALM model system enable the explicit representation of urban morphology and surface characteristics and are therefore well suited to investigate how urban densification and soil sealing modify local microclimatic conditions and potentially amplify urban heat island (UHI) effects. While microclimatic impacts of specific urban development projects within city borders already received wide attention in different studies, the microclimatic interrelations of large-scale suburban developments based on different scenarios still require more detailed evaluation in the research community.

This contribution presents first results from the INTERFERE project, where the PALM model system is applied to investigate how business-as-usual (BAU) and future regional development pathways influence suburban climate conditions around the city of Graz (Austria) by addressing suburban growth, infrastructure expansion, and associated land-use changes. Two spatial development scenarios are examined: 1) A BAU scenario assumes continuation of current planning practices, including full utilisation of designated building land that has not yet been developed, limited targeted densification, expansion of transport infrastructure, and no reduction of existing development reserves. 2) In contrast, a climate-sensitive planning scenario (Best Practice - BP) follows similar development constraints but emphasises compact urban development and targeted densification—particularly around public transport corridors—enhanced greening measures, and reduced land take through more efficient use of existing reserves. The spatial development scenarios are derived from official zoning and regional planning instruments and are developed by a local spatial planner, who is actively involved in supra-regional and regional planning processes in Styria to ensure realistic scenarios and policy-relevant future pathways. The resulting land-use configurations are than translated into the PALM model system.

The PALM simulations are driven by boundary conditions from high-resolution mesoscale modelling (WRF coupled with the Town Energy Budget model, TEB; Trimmel et al., 2021) at 300 m resolution, provided within the project. Since the mesoscale forcing explicitly accounts for urban structures and urban energy exchange processes, it provides a substantially more realistic representation than forcings from large-scale reanalyses products. For each scenario, a 30-hour heatwave episode, including a spin-up phase, is simulated based on a historical extreme summer event.

By explicitly linking regional spatial planning scenarios with high-resolution microclimate modelling, this study provides new insights into how suburban development patterns influence heat exposure and thermal comfort. In a next step, the results will be discussed with local mayors and key stakeholders to identify and derive appropriate counteracting measures, which will subsequently be assessed through additional simulations. The findings, to be presented at this conference, aim to support evidence-based spatial planning and climate adaptation strategies under increasing heat stress.