Urban Physics Modelling

The current world-wide urbanization trend comes with significant environmental costs and detrimental impact on the health and well-being of the city dweller. Understanding urban physics is one of the most effective tools at the disposal of the professionals in charge of mitigating the adverse effects of urbanization. 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). It is noteworthy that long-term phenomena are usually affected by global warming—which may require coupling with a global atmospheric model. Thanks to rapid scientific and computational developments in the past few decades, urban physicists have increasingly applied their expertise to real-life applications that are relevant to non-specialist concerned parties such as municipalities, environmental policy makers and urban planners. In particular, urban physics analysis can now accurately characterize and forecast urban heat island, buildings energy demand, thermal comfort and pollutant dispersion at high spatial and temporal resolutions.

End users of urban climate intelligence are diverse and cover different jobs, goals, and needs. Some need to understand the specific mechanisms underlying a certain climatic phenomenon while others need to forecast, plan or mitigate it. Examples include:

  • high-resolution spatial mapping of the current or future urban heat island (municipalities)
  • flood control (municipalities)
  • avoidance of heat stress or air pollution (public health authorities, city dwellers)
  • energy supply planning (energy utilities, grid operators))
  • probabilistic forecasting of extreme events (public safety agencies, insurance companies)
  • impact analysis of urban vegetation, green roof/wall, cool surfaces, photovoltaics (national energy policy decision makers)
  • combined effect of urban heat island and global warming (municipalities, national energy policy decision makers)
  • urban design optimization (urban planners)
  • climate-aware building design (architects and building energy engineers)

The goal of this group is to address the needs of a wide spectrum of end-users while following best practices in urban climate monitoring and analysis. Urban physics is a vast and complex field and we recognize the importance of tailoring the solution to the time constraints set by the end users’ decision/design processes. To this end, three modeling approaches are proposed. Mesoscale models incorporating the urban canopy parameterization aim to resolve the urban climate with horizontal grid resolutions of several hundred meters. The implementation of micro-scale models is necessary if higher horizontal grid resolutions are required. These Computational Fluid Dynamics (CFD) models consider the interactions between the atmosphere and the urban structures, with comprehensive physics-based 3D flow analysis. Both above-mentioned modeling approaches are computationally intensive, especially for longer simulation periods. This makes their use in a decision analysis context, where, typically, multiple full-year simulations of the urban micro-climate are required, problematic. Uncoupled urban canopy models are significantly less computationally intensive than both meso-scale and micro-scale CFD models. The 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.

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
 

Mesoscale models

Mesoscale models incorporating the urban canopy parameterization are used to resolve the urban climate with horizontal grid resolutions of several hundred meters.

 

Microscale urban climate analysis

Building and vegetation-resolved urban climate simulations are used to analyze and optimize specific urban planning issues.

 

Decision support for urban planning

Computationally light uncoupled urban canopy models are used in a decision analysis context.