Implementation of an Urban Parameterization Scheme into the Regional Climate Model COSMO-CLM

As the nonhydrostatic regional model of the Consortium for Small-Scale Modelling in Climate Mode (COSMO-CLM) is increasingly employed for studying the effects of urbanization on the environment, the authors extend its surface-layer parameterization by the Town Energy Budget (TEB) parameterization using the tile approach for a single urban class. The new implementation COSMO-CLM+TEB is used for a 1-yr reanalysis-driven simulation over Europe at a spatial resolution of 0.11 degrees (similar to 12 km) and over the area of Berlin at a spatial resolution of 0.025 degrees (similar to 2.8 km) for evaluating the new coupled model. The results on the coarse spatial resolution of 0.11 degrees show that the standard and the new models provide 2-m temperature and daily precipitation fields that differ only slightly by from -0.1 to +0.2 K per season and +/- 0.1 mm day(-1), respectively, with very similar statistical distributions. This indicates only a negligibly small effect of the urban parameterization on the model's climatology. Therefore, it is suggested that an urban parameterization may be omitted in model simulations on this scale. On the spatial resolution of 0.025 degrees the model COSMO-CLM+TEB is able to better represent the magnitude of the urban heat island in Berlin than the standard model COSMO-CLM. This finding shows the importance of using the parameterization for urban land in the model simulations on fine spatial scales. It is also suggested that models could benefit from resolving multiple urban land use classes to better simulate the spatial variability of urban temperatures for large metropolitan areas on spatial scales below similar to 3 km.