Urban Trees and Their Effect on Outdoor Thermal Comfort in Tropical Climates: A Miami Case Study

Outdoor thermal comfort is a critical factor that directly impacts health and quality of life in urban environments. With the increasing prevalence of urban heat islands (UHI) and rising global temperatures due to climate change, thermal comfort has become a central consideration in urban planning and design. In this research, we examine the role of urban trees in enhancing outdoor thermal comfort by conducting a comparative analysis between a tree-shaded area and a control site without vegetation in the Florida International University Modesto A. Maidique Campus, Miami, Florida. We use the Universal Thermal Climate Index (UTCI), a comprehensive human thermal comfort index for outdoor conditions, which accounts for thermo-physiological interactions and meteorological data. The study quantifies thermal comfort under tree canopies by analyzing key environmental variables, including air temperature, humidity, wind speed, and solar radiation—critical factors that influence human comfort in outdoor spaces. Solar radiation is estimated using a computational fluid dynamics (CFD) model and cloud cover data, while temperature, humidity, and wind speed are measured onsite with sensors. The results show that urban trees substantially improve thermal comfort, especially during midday when solar radiation and ambient temperatures are at their highest. Additionally, the study explores the temporal variations in thermal comfort throughout the day, emphasizing the dynamic relationship between environmental parameters and the cooling effects provided by tree.