Insights from an Experimental Campaign to Assess Urban Outdoor Comfort Conditions

Changes in urban surfaces and materials and decreased green spaces link urbanization to increased outdoor thermal discomfort. Thermal comfort indices can offer valuable insights into how urban design elements, particularly vegetation, influence human thermal perception. This study employs the Universal Thermal Climate Index (UTCI) to investigate how urban vegetation, and other surfaces affect outdoor thermal comfort in Milan, Italy. To this purpose, a measurement campaign was conducted during Summer 2023, gathering data to evaluate the UTCI across various urban settings and climate conditions. Specifically, vegetated green spaces (green sites) and spaces dominated by buildings and asphalt (grey sites) were compared. Correlation analyses were then performed to identify the key factors influencing UTCI at each location. The environmental conditions were comparable only on July 17th (green) and 19th (grey). On both dates the UTCI was primarily influenced by direct and reflected radiation in the morning. In the afternoon, re-emitted energy from surrounding materials sustained rising trends in air temperature and mean radiant temperature, thereby sustaining increases in UTCI. On July 19th, the thermal stress was higher, correlated with global radiation and mean radiant temperature all day. On July 17th also relative humidity and air temperature showed influence on UTCI.