Intra-urban differences of outdoor thermal comfort in Ghent on seasonal level and during record-breaking 2019 heat wave

Abstract

A comprehensive analysis of meteorological (air temperature, relative humidity, wind speed and global radiation) and outdoor thermal comfort (OTC) conditions (Physiological Equivalent Temperature and Mean Radiant Temperature) was carried out in six Local Climate Zones (LCZs) in Ghent (Belgium) on annual and seasonal level (2017) and during two heat waves (moderate in 2017 and record-breaking in 2019). The continuously monitored data originates from the local urban climate network MOCCA (MOnitoring the City's Climate and Atmosphere). The maximum hourly urban heat island (UHI) of 8.7 °C was noticed during the record-breaking 2019 heat wave. OTC was calculated with RayMan based on the observations from the MOCCA network and characteristics of the micro-environment which affect the estimated OTC conditions. The results show that cold stress is more apparent in Ghent during all seasons, except for summer. Downtown locations had more comfortable conditions on seasonal and annual level when compared to the rural location which had the most uncomfortable OTC conditions mostly due to cold stress. However, during the daytime period of heat waves, the open downtown and rural location were most frequently exposed to extreme heat stress, while the urban park in the sparsely built LCZ was the most comfortable area because it was able to effectively mitigate heat stress. This study illustrates the subtlety of the results of a thermal comfort study if one investigates both heat and cold stress on a yearly basis and during the extreme heat wave periods in a city with a moderate climate.