Optimizing pedestrian thermal comfort in urban street canyons for summer and winter: Tree planting or low-albedo pavements?

Urban heat islands and climate change are intensifying thermal discomfort in cities, particularly in densely populated street canyons. Studies show that optimizing surface albedo can positively affect human thermal comfort, but the impact of high versus low albedo materials remains controversial, with mechanisms still not fully understood. This study systematically investigated the effect of different albedo pavements on thermal comfort in street canyons using albedo measurements, experimental data, and simulations, factoring in tree cover and seasonal variations. Results indicate that although low-albedo pavements increase air and surface temperatures and long-wave radiation, they enhance thermal comfort by reducing reflected shortwave radiation, lowering the Physiological Equivalent Temperature (PET) by up to 3.9 °C in summer. Tree planting was more effective, reducing PET by up to 27.9 °C. Under tree or building shade, albedo changes had minimal impact on thermal comfort. In summer, both tree planting and low-albedo materials improve thermal comfort, while in winter, PET reductions may cause cold discomfort. Evergreen trees are recommended for hot-summer-warm-winter regions, and deciduous trees for hot-summer-cold-winter areas. These findings suggest urban planners prioritize tree planting for its cooling effects in densely populated areas, and use low-albedo materials in open, unshaded areas to reduce reflected radiation and enhance comfort.