A new urban parameterization for the ICON atmospheric model: first results over Italy

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.