Remote sensing based urban heat risk and thermal comfort assessment at a regional scale

Urban areas, characterized by high and rapidly growing populations, face an increased risk of extreme temperature events due to the urban heat island (UHI) effect. While elevated air temperatures (Ta) are the primary driver of discomfort, additional factors such as humidity, solar radiation, and wind also play a role in determining thermal comfort. Indices like the Universal Thermal Climate Index (UTCI) are commonly used to evaluate these combined effects. However, the sparse distribution of measurement stations within urban areas often limits the spatial resolution of such assessments. To mitigate this limitation, remote sensing techniques are frequently utilized, providing land surface temperature (LST) data as a proxy for air temperature. Although this approach improves spatial coverage, it may underestimate the true risk of heat stress, since the relationship between Ta, LST and thermal comfort metrics are not yet well understood.

To improve the assessment of heat risks and to analyze the interplay between different heat stress parameters, we examined the diurnal and spatial variations of Ta, LST, and thermal comfort indices at a 1 km resolution across the federal state of Hesse, Germany. Temperature anomalies (ΔT), calculated as the difference between local and rural baseline temperatures were utilized to distinguish urban heat effects from larger-scale climatic influences. Additional satellite-derived parameters were also incorporated to assess regional heat risk in areas lacking local measurement data, thereby achieving R² values above 0.9 on the test dataset. By providing an enhanced understanding of heat stress patterns and capturing spatial variations in urban and rural climates, this regional-scale approach enhances the understanding of how environmental hazards intersect with population vulnerabilities in the context of thermal comfort and supports in the design of more precise urban planning and risk mitigation strategies.