Evaluating the effects of different tree species on enhancing outdoor thermal comfort in a post-industrial landscape

Abstract

A frequently emphasized strategy to reduce the burden of heat in cities across the world is the implementation of street trees. Here, we examine the effects of deciduous and coniferous tree deployment on meteorological variables and pedestrian thermal comfort through analysis of the new dynamic thermal comfort (dPET) index, using the latest version of the computational fluid dynamics model ENVI-met. We performed on site observational measurements of air temperature (Ta), relative humidity (Rh), wind speed (Ws), and mean radiant temperature (MRT) at five different locations on the hottest day of summer 2023, in a post-industrial urban landscape located in Tehran, Iran. Observations were used to evaluate ENVI-met simulation performance and served as a baseline against which sensitivity experiments—based on a minimum (35%) and maximum (75%) intervention scenario for deciduous and coniferous trees—were compared against. Our analysis indicates that 35% and 75% deployment reduced Ta by 1.2 °C and 4.2 °C, respectively, for deciduous tree species, compared to a 0.9 °C and 3.1 °C reduction for coniferous species, during the hottest day of summer 2023. The maximum deployment scenario decreased MRT by approximately 60 °C and 43 °C for deciduous and coniferous tree deployment, respectively. The maximum tree deployment scenario decreased dPET by nearly 16 °C and 14 °C for deciduous and coniferous trees, respectively, during the time of day that diurnal heating is maximized. Our findings highlight micrometeorological and personalized thermal comfort effects associated with variable tree species type and extent through examination of a pedestrian’s ambulatory experience across diverse urban microclimates in a region of the world that is particularly understudied.