Evaluation of surface temperatures by material type and shading conditions in urban open spaces: The case of Lisbon, Portugal

This study aims to evaluate the surface temperatures of different materials under sun-exposed and shaded conditions, as well as variations in local ambient air temperature, in urban open spaces with moderate to high levels of pedestrian use in central Lisbon. Field measurements were conducted between 20 and 25 May 2025. A total of 852 surface temperature measurements collected over six days from 142 distinct surface points and 138 ambient air temperature measurements from 23 locations were analyzed using mixed-effects models. Under sun-exposed conditions, surface temperatures differed significantly among material types; artificial turf, composite materials, and asphalt showed higher temperature values, whereas natural grass showed lower values. No significant differences among material types were found under shaded conditions. The effect of sun/shade conditions varied by material type, with the largest temperature difference observed for asphalt. In the complementary color analysis, dark-colored surfaces were 8.6°C warmer than light-colored surfaces under sun-exposed conditions, while no significant difference between the color groups was observed under shaded conditions. Ambient air temperatures were highest in hardscape settings surrounded by other hard surfaces. Points within tree-covered, park-like surroundings showed lower temperature values, while water-edge settings were also cooler than hardscape settings. Within water-edge settings, however, no significant difference was found according to whether the surrounding environment consisted of hard surfaces or tree-covered, park-like surroundings. The findings indicate the importance of considering material selection, shading, surface characteristics, vegetation, and proximity to water together in the design of urban open spaces.