Modelling the Urban Heat Island over Turin during past heat waves

Urban Heat Island (UHI) is a phenomenon where urban areas experience significantly higher temperatures than their rural surroundings. This effect is primarily due to heat retention in buildings and roads, reduced evapotranspiration, and heat generated by vehicles, industrial activities, and air conditioning. Accurate UHI modelling is crucial for understanding its impacts and helping urban planners and policymakers in developing effective strategies to mitigate heat stress in cities. Advanced urban canopy schemes within atmospheric models play a key role, as they aim to realistically represent the complex interactions between urban surfaces and the atmosphere. The TERRA_URB (TU) model, developed within the COSMO Consortium, parametrizes the effects of buildings and streets on energy and moisture exchanges between the surface and atmosphere. Additionally, it accounts for the anthropogenic heat flux as a heat source from the surface to the atmosphere. TU requires the definition of parameters describing the geometrical and thermal urban features, such as street aspect ratio, building surface fraction, building height, impervious surface area, anthropogenic heat flux. These parameters were derived from the Local Climate Zone (LCZ) classification, using both global and local dataset. This study evaluated the performance of the TU scheme, implemented within the ICON model, by simulating past heat waves over Turin at 500 m resolution in hindcast mode. The ability of the TU scheme to reproduce UHI effects was assessed by comparing ICON simulations, with and without TU, against observational data. These included ground-level measurements from the Arpa Piemonte meteo-hydrological network and vertical temperature profiles from radiometers located in both the city center and surrounding areas. Furthermore, a denser crowdsourced air temperature network, NetAtmo, was evaluated to assess the potential of the citizen science data for improving urban climate studies. The results demonstrated that the TU scheme significantly improved the representation of the UHI effect.