Impact of rainfall on air temperature, humidity and thermal comfort in tropical urban parks

Urban areas in hot and humid tropical regions are frequently exposed to uncomfortable thermal levels. A well-developed urban heat mitigation strategy is increasing vegetation infrastructure, even though the impact differs based on regional climate. In this study we have evaluated the impact of rainfall on air temperature, humidity and thermal comfort inside a large urban park in Singapore, based on measurement campaigns. A comparison between the park and an urban site is presented. Results show that rainfall significantly reduces air temperature and improves thermal comfort levels, not only right after the rain event but also in the after-event dry period. The cooling potential of rainfall depends not only on the intensity and duration of the event, but also on the weather conditions after the event, especially incoming solar radiation. The maximum cooling potential of rainfall is lower in the park but also the park tends to stay cooler longer (lower recovery of air temperature recuperation) after the rain event. An increase of humidity after the event does not prevent an improvement in thermal comfort levels inside the park. Overall, results provide a grounded argument for the promotion of use of parks after rain events, especially during daytime.