Thermal and humidification effects of a swimming pool in Hong Kong's humid-subtropical summer

Abstract

The microclimatic effect of small urban water bodies such as swimming pools has received little attention. This study aimed at (1) comparing the microclimate adjacent to a swimming pool against two control sites and (2) quantifying the pool's cooling and humidification effects. We employed high-precision sensors to measure air temperature, atmospheric vapour pressure, black-globe temperature, and incoming and outgoing radiation at a swimming pool, nearby tennis court and turf sites in Hong Kong's humid-subtropical summer. On sunny days, we found a maximum poolside air temperature of 36.6 °C at 0.15 m height. The highest vapour pressure of 3.14–4.13 kPa occurred on cloudy days. Cooler rainy days lowered vapour pressure. Net short-wave radiation gain peaked at 840 W/m2 on sunny days. The findings suggested that energy stored by the pool in the morning retarded surface cooling later in the day. The morning poolside surface temperature was cooler than the turf by 3.8 °C but warmer by 5.7 °C in the afternoon, with lingering nighttime warming. Unexpectedly, the pool had lower vapour pressure than the control sites. The water body does not ameliorate heat stress on the deck in sunny conditions. The findings hinted that larger recreational blue spaces might generate more thermal and humidification effects.