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<p>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 parameterization 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 needs to be implemented in ICON. Furthermore, an updated set of urban canopy parameters needs to be provided, for describing the urban characteristics down to a mesh size of 1 km, and below. For these purposes, the COSMO Consortium organises the dedicated Priority Project CITTA’. First results are presented for TERRA_URB in the ICON limited-area model ICON-LAM for different cities of interest of the CITTA’ partners. The preliminary results indicate already that urban features like the urban heat island effect are well represented. This is in agreement with the experiences with TERRA_URB in the COSMO model, both the climate as well as the NWP version.</p>

The increase in the resolution of atmospheric models for numerical weather prediction and climate simulations allows for a more accurate description of the physical processes at urban scale. Furthermore, a common trend is occurring in most countries: the number of people living in towns keeps on growing remarkably, therefore it becomes increasingly important to study the living conditions in urban or metropolitan areas under demographic and climate change. In these scenarios, the interest in properly modelling the physical processes in urban areas has gained wide attention in the research community. In particular, the convection-permitting atmospheric models, associated with urban parameterizations, are able to resolve the heterogeneity of cities with applications to heat stress assessment and the development of urban climate adaptation and mitigation strategies. In this perspective, a bulk urban canopy parameterization, TERRA_URB, has been developed for the multi-layer land surface scheme of the COSMO regional atmospheric model. This parameterization has already demonstrated to be able to accurately describe the overall properties of urban areas and to correctly reproduce the prominent urban meteorological characteristics for different European cities. Thus, in the framework of the transition from the COSMO model to the new Icosahedral Nonhydrostatic (ICON) Weather and Climate regional model, TERRA_URB needs to be implemented in ICON. In this work, we present the results for TERRA_URB in ICON-LAM (the limited area model version), for some cities of the Italian peninsula at a mesh size of 2 km. At this stage of the implementation, although further investigations in calibration and in the use of more realistic urban canopy parameters are needed, the preliminary results are really encouraging, since some urban key features are already properly represented, such as urban heat island and urban dry island phenomena. The comparison of these results with available observations is promising. Therefore, this work provides strong evidences regarding the added value of TERRA_URB to ICON in modelling the complex urban canopy interaction processes with the atmosphere.