Monitoring Microscale Heat Stress Patterns in a Medium-Dense Urban Area with Green Spaces

Abstract Urban areas are increasingly vulnerable to heat stress due to climate change and the urban heat island effect. Heat stress is influenced not only by air temperature but also by humidity, wind speed, and radiation, resulting in a meter-scale variability across different microenvironments, making observational campaigns challenging. One measurement strategy consists of deploying a significant number of consumer-grade portable measurement devices, which often have limited accuracy and reliability. This paper thoroughly evaluates such an approach through a dense meter-scale measurement campaign in the urban fringe of Ghent (Belgium). Utilizing both low-cost AT-HTS01 devices and research-grade weather stations, this study evaluates the wet-bulb globe temperature (WBGT) indicator to assess heat stress during a heat wave. Results show that, despite their limitations, the consumer-grade devices can provide WBGT values comparable to research-grade stations, enabling their use for a detailed analysis of microenvironmental impacts on heat stress. The measurement campaign confirms that daytime heat stress is largely influenced by direct solar radiation and effectively reduced by shading: building shade decreased WBGT by 4.3°C and tree shade by 3.5°C. However, the solar-exposed side of the building increases heat stress, making trees the most effective measure against heat stress. At night, unpaved surfaces reduce heat stress by 0.8°C WBGT. The outcomes of this study are valuable for designing future measurement campaigns, informing street-scale heat resilience strategies, and validating meter-scale numerical heat stress simulations. Significance Statement Heat stress, a growing threat to human health, depends on air temperature, humidity, wind speed, and radiation. However, little is known about its fine-scale variability across different microenvironments or how it can be captured using affordable tools. This study addresses these challenges through a high-resolution measurement campaign using consumer-grade portable devices alongside research-grade weather stations. The results offer a practical approach to accurately monitor heat stress using simple tools and calculation methods. Findings reveal that building shade reduces heat stress more than tree shade. However, the solar-exposed side of the building increases heat stress, making trees the most effective measure against heat stress. Small unpaved surfaces decrease nighttime heat stress. These results highlight street-scale strategies to enhance heat resilience.