Implementation and testing of the building energy parameterization model (BEP) in the Climate Local Model (CLM)

The multi-layer urban surface parameterization scheme BEP was implemented in the mesoscale numerical weather and climate model COSMO-CLM to enhance the application of the model to urban areas.

In BEP the urban morphology is represented by generic street canyons which are defined by building and street width, building height distribution and canyon orientation. In the mesoscale model, BEP enables the consideration of the effects of buildings on momentum, heat, radiation exchange and turbulent kinetic production in the planetary boundary layer calculations. BEP is applied to the fraction of a model grid cell that is covered by impervious surfaces while a soil and vegetation model is applied to the fraction cover of natural surfaces.

The model is first applied to the city of Berlin, Germany for an extreme heat event in the summer of 2003. An algorithm was developed that computes BEP input parameters for each model grid cell based on a 3d building model that covers the entire city of Berlin (CityGML format; >460000 buildings).

Simulations were compared with observations from surface meteorological stations. Results show a significant improvement of the CLM model performance with the application of BEP over the original roughness approach. In addition, the results are compared to calculations using a land use class approach for the BEP input parameters. Furthermore, the effect of considering roofs in the radiation budget are presented.