UV Parasol, Dry-Mist Spraying, and Street Trees as Tools for Heat Stress Mitigation

抄録

 Ultra Violet (UV) parasols are a reasonable countermeasure against heat stress as they are portable and inexpensive. This study compared the heat stress mitigation effect of a UV parasol with that of street trees and dry-mist spraying on a hot and humid summer day in Japan. We observed meteorological elements and calculated the universal thermal climate index (UTCI) and wet-bulb globe temperature (WBGT) under UV parasol, street trees, dry-mist spraying, and direct sunlight. The observed UTCI and WBGT under the UV parasol were lower than those in direct sunlight by 4.4 and 1.3°C, respectively, because of the decrease in black globe temperature caused by the reduced downward shortwave radiation. This demonstrated that UV parasol reduced heatstroke risk by one level. The effect of the UV parasol was equal to or greater than 75 % of that of the street trees from the perspective of UTCI. The street trees reduced the UTCI and WBGT by 5.9 and 1.9°C, respectively, compared to those in direct sunlight, resulting in the reduction of heatstroke risk by one level. In contrast, dry-mist spraying did not mitigate heat stress in conditions with moderate winds. Although the results of this study were obtained from observations on a single day, comparison with earlier studies confirms that the values observed in this study are representative results on summer days in Japan.