Urban Physics Modelling

The current world-wide urbanization trend comes with significant environmental costs and detrimental impact on health and well-being of the city dweller. Urban climatic phenomena encompass both high frequency and low frequency events. These events may be analyzed over the short-term (days to weeks) or the long-term (a year or more). Long-term phenomena are usually affected by global warming—which may require coupling with a global atmospheric model. Thanks to rapid scientific, computational development in the past few decades, urban physicists can now apply their expertise to real-life applications: urban heat islands, buildings energy demand, thermal comfort and pollutant dispersion at high spatial and temporal resolutions. By means of the urban building physics investigations, urban planning conditions and decisions can be comprehensively characterised or weighed up at an early stage.

Three modeling approaches are important for Fraunhofer IBP’s research:

• Mesoscale models represent the urban climate with horizontal grid resolutions of several hundred meters. 
• Microscale models from Computational Fluid Dynamics (CFD) offer a higher resolution and consider the interactions between the atmosphere and the urban structures, with comprehensive physics-based 3D flow analysis.
• While these modeling approaches are computationally intensive, especially for longer simulation periods, uncoupled models allow faster calculations. The simplified urban canopy model at the heart of this third modeling approach is similar to the urban parameterization implemented by meso-scale models. However, it is not coupled to a full meso-scale atmospheric representation and is instead forced by boundary conditions that are directly measured or derived from an off-line meso-scale simulation.

Our models make use of:

• comprehensive urban meta-data (land-use, 3D morphology)
• in-situ measurements of urban meteorological variables, possibly at multiple locations throughout the city and at multiple heights
• remote sensing of land cover, land surface temperature and aerosol concentration
• drone-based measurement of urban boundary layer properties