Investigating urban heat islands over Rome and Milan during a summer period through the TERRA_URB parameterization in the ICON model

The urban heat island (UHI) effect, influenced by various built environment factors, significantly impacts human wellbeing. Detailed studies and interdisciplinary collaborations are crucial for understanding and quantifying this phenomenon and developing effective and targeted strategies to address issues related to the UHI effect. Variability in UHI temporal patterns and magnitudes poses challenges for accurate atmospheric modeling. In order to reproduce UHI dynamics, numerical models account for urban features through urban canopy parameterizations. This work presents encouraging results on the implementation of the urban scheme TERRA_URB (TU) in the ICOsahedral Nonhydrostatic (ICON) atmospheric model. The results of high-resolution ICON simulations, with and without TU, are compared against observational data and COSMO model results, where TU was already well established, for the Italian cities of Rome and Milan during the month of August 2017. The main outcome of this study is the satisfactory implementation of TU in ICON, as it reasonably reproduces UHI effects and improves air temperature forecasts for the investigated urban areas. The results constitute an update of numerical weather prediction and climate simulations for urban modeling applications, while further investigations aimed at enhancing the calibration of the model parameterization and introduction of more realistic urban canopy parameters are planned. • TU implementation in ICON is completed and investigations for Rome and Milan during summer period are encouraging. • ICON with TU parameterization improves UHI dynamics, distinguishing urban/rural signals vs both station data and COSMO model. • ICON-COSMO differences may rely to different tile approach formulation, physiographic parameters, and intermodal variability. • ICON replaces COSMO for regional weather and climate modeling; future modeling developments will focus entirely on ICON.