Spatial Estimation of Thermal Indices in Urban Areas—Basics of the SkyHelios Model

Thermal perception and stress for humans can be best estimated based on appropriate indices. Sophisticated thermal indices, e.g., the Perceived Temperature (PT), the Universal Thermal Climate Index (UTCI), or the Physiologically Equivalent Temperature (PET) do require the meteorological input parameters air temperature ( T a ), vapour pressure ( V P ), wind speed (v), as well as the different short- and longtime radiation fluxes summarized as the mean radiant temperature ( T m r t ). However, in complex urban environments, especially v and T m r t are highly volatile in space. They can, thus, only be estimated by micro-scale models. One easy way to apply the model for the determination of thermal indices within urban environments is the advanced SkyHelios model. It is designed to estimate sky view factor ( S V F ), sunshine duration, global radiation, wind speed, wind direction, T m r t considering reflections, as well as the three thermal indices PT, UTCI, and PET spatially and temporarily resolved with low computation time.