How are green spaces effective in urban heat island mitigation? A case study in northeastern Italy

The urban heat island (UHI) is an important and current issue in most urbanized areas. It can be particularly harmful to human health and there are numerous studies that link mortality and morbidity with extreme thermal events, that can be worsen by UHI. The temperature difference between city centers and the surrounding countryside, which is accentuated in the summer months and at night, is the result not only of a greater production of anthropogenic heat but also and above all is linked to the materials cities are made from. The use of vegetation, and in particular urban tree planting, constitutes one of the most effective strategies in contrasting the heat island effects. In order to analyze the mitigation effects produced by green spaces in the city center of Padua, a municipality in the northeast of Italy, simulations of the air temperature trends and their spatial distribution were carried out using the i-Tree CoolAir model. The extreme conditions for maximum summer temperatures, the UHI effects become more critical, were considered in the study. A particularly hot July day was chosen, with recorded air temperatures respectively of 35°C at 3 pm and 28°C at 10 pm, at a reference weather station. The results of the simulation show temperature differences up to almost 10°C in the daytime (3 pm) between urban open spaces with impervious cover (squares, streets) and green areas. These differences are related to the shading effect of the tree canopy. Although at night (10 pm), the air temperature differences are less evident. Once again, impervious open spaces maintain air temperatures 4°C higher than those recorded at the weather station, while in areas with tree cover temperatures are about 2°C lower.