On the Parametrization of Urban Land Use in Mesoscale Models

The effects of urban structures on the distribution of meteorological variables can be included in mesoscale models by an appropriate parametrization. The different approaches are conventionally tested against wind profiles in the centre of the urban area while flow distortions around are not considered. In this study, the quality of different parametrizations in capturing the main wind-field modifications in, as well as around, a complex obstacle is investigated. The method applied consists of a building resolved microscale model and a mesoscale model including a suitable parametrization. The results demonstrate that a drag or a porosity approach can reproduce very satisfactorily the main characteristics of the airflow completely, while a simpler roughness length concept in general approximates the mean flow unsatisfactorily.