Abstract: Climate change will alter thermal comfort very differently depending on the future scenario selected. This research computes two bioclimatic indices: Physiological Equivalent Temperature (PET) and Universal Thermal Comfort Index (UTCI), in the area of Tabriz (Iran), considering an observational period (1960 to 2020) and three projected scenarios (RCP2.6, RCP4.5, and RCP8.5) associated to greenhouse gas concentrations for the period 2030 to 2059 and 2060 to 2100. The CanESM2 model was used to estimate projected data. Thermal comfort for these three periods are compared at daily basis attending to the sky conditions (clear and cloudy) and the presence or absence of wind. The study of the observational period shows that the cloud cover effect has increased PET and UTCI values by 0.82 and 0.51°C, respectively. For the projected period, it has been found an increase in PET and UTCI values by 0.36 and 0.42°C associated to the presence of clouds. On the other hand, a decrease in temperature of 10°C for PET and 11.73°C for UTCI is found in the observational period when windy and calm days are compared. This cooling effect of the wind will decrease in the projected period where temperature reduction based on PET and UTCI values is estimated to be 4.5 and 8.4°C for 2030-2059 and 2.5 and 5.2°C for 2060-2100 respectively. In conclusion, future changes in clouds and wind will clearly impact thermal comfort in the city of Tabriz in the future decades. Both the projected cloudy heating effect and the reduction of the potential of cooling of the wind, will have serious implications for heat-related diseases and different socioeconomic activities in the region. Accordingly, the definition of mitigation and adaptation strategies in short term should be a priority.

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