Assessment on outdoor thermal comfort conditions in the capital Phnom Penh, Cambodia

Thermal microclimate in cities has been noticeably changed due to the rapidity of urbanization and climate change. The thermal alteration in the built environment of cities results in a number of urban problems linked with human well-being. Since heat stress is one of the serious environmental threats to human health, it can leave urban communities at a risky threshold. In particular, cities located in the hot-humid climate are more vulnerable to the mounting thermal conditions. Nonetheless, outdoor thermal conditions in the tropical climate have not been fully observed. There is much need for investigation focusing on both physiological and psychological influences to determine thermal environments on the micro-scale.

The main aim of this present study is to understand outdoor thermal conditions in the tropical climate of Phnom Penh. The investigation of outdoor thermal comfort was performed through the Physiologically Equivalent Temperature (PET) index based upon the measurement of climatic parameters. Simultaneously, a questionnaire survey was utilized to capture psychological perception with response to thermal conditions. The field survey was conducted in three different types of outdoor spaces in Phnom Penh to observe thermal circumstances. one is a low-rise area adjacent to a river with fewer shades, second is a medium-rise area and the last is a high-rise area.

Depending to the PET calculation, the results represent very low thermal comfort in the outdoor environment of the city while strong and extreme heat stress occurred all the time during the survey period. The thermal conditions far exceeded the comfortable range. Among all climatic parameters, solar radiation has the strongest influence on the physiologically thermal comfort level in the outdoor environment. Even though under the hot temperature outside, the thermal condition is still acceptable according to the psychological responses of participating outdoor users. Furthermore, the study indicates a major difference between thermal conditions from the physiological index and the psychological responses. Greater tolerance of the outdoor users to the hot environment is found, in comparison with the physiological outcomes. Besides the climate effect on the outdoor thermal comfort level, the study also shows a significant influence of physical adaptation. The proper characteristics of spatial setup are able to mitigate the individual thermal comfort. Finally, the study gives some recommendations for better outdoor thermal conditions in order to enhance urban life and promote outdoor activities in hot-humid environments.