A new urban parameterisation for the ICON atmospheric model

A new urban canopy scheme for the ICON atmospheric model is presented. Increasing the resolution of atmospheric models for numerical weather prediction (NWP) or climate simulations allows, among others, for a more realistic description of the processes at the land surface. Here, one field of growing interest are the processes in urban areas. Beside their relevance for the meteorological modelling, there is a general trend in most countries that the number of people living in towns is significantly increasing. During the recent years, an urban canopy parameterisation was developed for the multi-layer land surface scheme TERRA of the Consortium for Small-scale Modeling (COSMO) mesoscale atmospheric model. This parameterisation, TERRA_URB, originally developed for the climate version of COSMO and then ported to the NWP version, was shown to be able to reproduce the key urban meteorological features for different European cities. In the framework of the transition of the COSMO Consortium to the ICON model, TERRA_URB needed to be implemented in ICON. For this purpose, the COSMO Consortium organises the dedicated Priority Project CITTA’. Meanwhile, the implementation of TERRA_URB in ICON is completed. Beside this, CITTA’ addresses the important issue of the urban canopy parameters which are needed to characterize urban areas in the atmospheric model. Currently, ICON uses the land use dataset GlobCover which contains only one urban class. In order to improve on this, the advanced ECOCLIMAP-SG land use dataset is implemented in ICON, containing 10 urban land use classes being based on the concept of local climate zones. Results are presented for TERRA_URB in the ICON limited-area model ICON-LAM for different cities of interest of the CITTA’ partners. They indicate that features like the urban heat island and urban dry island effects are well represented. This is demonstrated on test cases like in the WMO WCRP FPS URB-RCC.