The metropolitan region of So Paulo (MRSP) is a densely populated area with approximately 20 million people. The impact of climate variability on the population can be estimated by the use of thermal comfort indexes. The aim of this work is to investigate the effect of projected climate change on the thermal comfort index, IPET (Indoor Perceived Equivalent Temperature), over MRSP, based on a two-weather-stations dataset. For this, four RegCM4 projections from the CREMA (CORDEX REgCM4 hyper-Matrix experiment) project for the representative concentration pathway 8.5 (RCP8.5) are used in two time slices: present (1975-2005), and future (2065-2099) climates. The IPET index is calculated for both present and future climates and the datasets are subdivided by quantiles, annual means and interpretative range categories. In the present climate, all simulation members are compared with two observed datasets representing the MRSP. The result of this comparison indicates that the simulation members properly represent the long-term means of the variables used in the IPET calculation. The trend analysis of all simulation members shows a warming pattern for IPET, which rises from 19.1-21.3A degrees C, for the present, to 23.5-25.1A degrees C, for the future climate. The spatial pattern indicates that the MRSP is located in a transitional zone where IPET in the future climate becomes higher than temperature due to the relative humidity increase. This result emphasizes that the increase of relative humidity plays an important role in increasing IPET. The simulations also indicate that the values of the lower and higher IPET quantiles will decrease and increase in the future, respectively. Considering thermal comfort, the IPET interpretative range distribution trends show a decrease of days in the "cool" category and an increase of days in the "warm" category. The overall results corroborate studies pointing to a warming pattern that could impact society in the MRSP. This could provide an important tool to promote the subsidization of Brazilian stakeholders wishing to take mitigative actions.
