Assessing Urban Sprawl and Densification Impacts on Local Climate Around Graz Using ICON and WRF

Urban sprawl intensifies the urban heat island (UHI) effect, leading to elevated temperatures in densely populated areas. This phenomenon, combined with the adverse impacts of soil sealing, highlights the urgent need for targeted investigation and mitigation strategies.The project INTERFERE examines suburban development, the consequences of urban sprawl, and densification strategies in the suburban areas surrounding Graz. Using local and regional expertise, future spatial development concepts were defined and simulated to assess the impacts of urbanization on the local climate.Two regional climate modeling systems were applied to simulate three development scenarios: Current, Business as Usual, and Adapted. The simulations were conducted using the ICON (ICOsahedral Nonhydrostatic) regional climate model with the TERRA_URB urban canopy module, and the Weather Research and Forecasting (WRF) model coupled with the Town Energy Balance (TEB) scheme. ICON is widely used for numerical weather prediction and climate simulations, including the assessment of urban climate effects such as the UHI. The TERRA_URB module enables the two-dimensional representation of urban land-surface processes and their interactions with the atmosphere, while WRF-TEB provides a detailed three-dimensional description of urban energy exchanges by accounting for radiative, convective, and conductive heat fluxes and explicitly representing urban structures and their influence on local climate conditions.A comparative analysis of ICON–TERRA_URB and WRF-TEB simulations is conducted for the suburban areas surrounding Graz, with a focus on how each modeling system represents regional development patterns and the resulting urban heat island effects during heatwave conditions. Differences in model outputs across the development scenarios are analyzed, alongside challenges related to computational efficiency and model calibration. The results emphasize the importance of model choice in relation to specific research objectives and urban-climate assessment needs.