Urban heat island in Padua, Italy: simulation analysis and mitigation strategies

Urban Heat Island effect was widely studied in large cities around the world, more rarely in medium size ones. The paper reports on the study of the UHI phenomenon in Padua, a medium size city of the North-East of Italy, one of the most industrialized and developed parts of the country. Experimental measurements were carried out during 2012 summer, recording the main thermo-hygrometric variables by mobile surveys along an exact path crossing different zones of the city area (urban, sub-urban and rural). Some measurements in situ in characteristic sites of the city area (like historic centre, high and low density populated residential zones, industrial zone, rural zone) were carried out in order to evaluate thermal comfort indexes. The analysis of the data highlights the presence of UHI effect with different magnitudes in function of the zone of the city. In the city centre, an historical zone, the effect was up to 7 °C. The ENVImet simulation model was used in order to quantify possible increases in thermal comfort as a consequence of some mitigation strategies. In particular, a very famous square of the city (Prato della Valle) was analysed: it can be considered representative of the phenomenon because of the size and so the very different characteristics from the UHI effect point of view. Two scenarios were analysed besides the actual one (“AsIs” scenario): “Green ground” (halving the asphalt surface and doubling the green and plants surface) and “Cool Pavements” (increasing the albedo of impervious horizontal surfaces). The simulations results are presented both in terms of UHI intensity (difference in air dry-bulb temperature between Prato della Valle and a reference rural site) and in terms of mean radiant temperature and thermal comfort sensation. The results are presented both in spatial and temporal terms for a typical summer day. The “Green ground” scenario allows till 1.4 °C and 3 °C decrease in air temperature, respectively during the night and the day. The same items for the “Cool Pavements” scenario are, respectively, 1.8 and 4 °C.