2020 Volume 57 Issue 2 Pages 81-94
This study examined whether the modification of an asphalt-paved road can mitigate pedestrians' heat stress in summer. The five test sections, i.e., the dense-graded, permeable, heat reflective, water-retaining asphalts and the lawn as a comparison material, were constructed with each having an area of 5 m × 5 m at a test field in Toyota city, Japan. The quantities observed at each test section were the vertical temperature distribution including air, surface and underground temperatures, downward/upward longwave radiation fluxes, downward/upward shortwave radiation fluxes, and evaporation rate, besides the air temperature and humidity, wind velocity and direction, precipitation, and global solar radiation at the representative point, and water content of the two small specimens of permeable and water-retaining pavers.
The surface temperature was the lowest on the lawn with the albedo of approx. 0.2, and the second lowest on the heat reflective pavement with the highest albedo of approx. 0.3. The water-retaining pavement had the slightly higher surface temperature than the heat reflective pavement and the albedo close to the lawn. This means the evaporative cooling reduced the surface temperature of the lawn and the water-retaining pavement. In contrast to the heat reflective pavement, the dense-graded and permeable pavements had the obviously higher surface temperatures with the lower albedos of less than 0.1, and the lower reflective solar radiation. Eventually, according to the calculation of the thermal index OET (Occupied effective temperature) which was newly derived, the effect of all-wave radiation on pedestrians was the highest on the heat reflective pavement, the second lowest on the water-retaining pavement, and the lowest on the lawn. The water-retaining pavement could be effective for reducing the human heat stress since the pavement made the evaporative cooling effect last longer than the lawn even if the sunny weather continued.
