An investigation on the radiant heat balance for different urban tissues in Mediterranean climate: a case study

The outdoor radiant field is a key aspect to determine outdoor comfort conditions for humans, especially in urban areas. In order to unveil the dependence of the radiant field on the features of the urban fabrics, this study analyses the space distribution of the Mean Radiant Temperature (TMRT) and the radiant field in various urban tissues of the city of Catania (Italy) in a typical Mediterranean climate. The study is based on simulations through the Solar and LongWave Environmental Irradiance Geometry model (SOLWEIG) implemented in UMEP. Results show that the worst conditions occur in areas with moderately deep urban canyons, abundant impervious surfaces and lack of vegetation: here, the TMRT can easily reach 78 °C while in more than 80% of the area it exceeds 60 °C. By modelling the time trends of the shortwave and longwave radiant heat fluxes perceived by a pedestrian, it has been possible to observe that the highest contribution to the outdoor radiant field comes from the downward solar irradiance. However, the downward and upward longwave radiant flux closely follows: this suggests the importance of providing shading rather than using highly reflective surfaces that can exacerbate heat stress by means of the increased reflected shortwave radiation.