Mitigation technologies for counteracting the UHI effects and for improving outdoor thermal comfort in mediterranean urban open spaces: a study of vegetation and cool materials effects on pedestrian comfort in Rome

The present study investigates the influence of building materials, traditional as well as innovative, and vegetated urban surfaces on the urban microclimate and on pedestrian outdoor thermal comfort in a typical Mediterranean city: Rome. It focuses the attention on selected mitigation technologies aiming to increase the albedo of cities: high reflective materials called cool colored materials, and the use of vegetative surfaces: green roofs, green walls and trees, with the main purpose to test, verify and quantify the overall microclimate mitigation and thermal performance of the aforementioned strategies, The study proposes and analyses, through CFD calculations (ENVImet v.4.0), five renovations scenarios: applying cool materials and vegetation on roofs, walls and pavements of the selected square. In order to support planning authorities and researches by going beyond the traditional way of urban heat island studies, the present study aims to highlight the multiple effects of cool colored materials on human comfort and to investigates which could be the best combination materials in terms of mitigation of ambient temperatures and pedestrian thermal stress. Therefore, air temperature as well as the physiologically equivalent temperature (PET) were applied to take into account the effect of the variations of urban materials on human comfort, the studies focuses the attention and draw its conclusions through the comparison of the Envimet thermal maps and the values of the different scenarios in terms of deltas variations. The results show the negative effect of cool colored materials on human thermal comfort when applied isolated to surfaces in direct contact with pedestrians, such as pavements and urban façades, nevertheless it underlines the benefit associated with a mixed combination of cool materials and trees, setting the path for further research in this direction.