Park design and pedestrian thermal stress: Evaluating the effects of shade and ground surface materials

This study examines the effects of tree shading and ground material properties on thermal comfort in an urban park in Florence Italy, using the Index of Thermal Stress (ITS) and Universal Thermal Climate Index (UTCI) to represent the energy balance between the human body and the environment. ITS and UTCI were evaluated over exposed gravel, asphalt and grass as well as tree-shaded paving. Findings indicate clear differences in thermal stress induced by each landscape treatment. A pedestrian in the unshaded gravel area would experience the most stressful conditions, while a person standing on the unshaded asphalt paving would be exposed to slightly lower thermal stress - highlighting the effect of reflected solar radiation on the body from the higher-albedo gravel surface, which more than compensates for the higher surface temperature and long-wave radiation emitted from the asphalt. The low surface temperature of the transpiring grass lawn affords conditions defined as "hot" for only a short time in the afternoon, with most daytime hours characterized as "warm". The most dramatic reduction in thermal stress occurs in the area shaded by trees: here a pedestrian would be exposed to conditions defined as "comfortable" for nearly all hours of a typical summer day.