Temporal and spatial patterns of heat extremes in Hesse, Germany

Abstract Elevated temperatures due to the Urban Heat Island (UHI) effect, combined with a high population density, increase the risk of heat-related illnesses in urban areas. Spatial data on heat stress is crucial for effective mitigation strategies in urban planning. However, meteorological parameters like air temperature (Ta) and relative humidity (RH), necessary for thermal comfort indices such as Physiological Equivalent Temperature (PET) and Humidex, are often unavailable at fine spatial resolutions. Consequently, Land Surface Temperature (LST) from spaceborne thermal sensors are commonly used as a substitute. Here we evaluate the spatial and temporal patterns of LST, Ta, PET, and Humidex by analysing urban-rural intensity differences (ΔT) in Hesse, Germany, at a 1 km resolution. The Humidex (max: 4.3 °C) dataset reveals an amplified UHI effect compared to Ta (max: 2.9 °C) and LST (max: 3.4 °C), suggesting that relying solely on LST or Ta may underestimate heat stress. While LST is often used to approximate Ta, there is high correlation to thermal comfort indices such as PET during the day (r = 0.49) and ΔHumidex (r = 0.47) at night.