Modeling of thermal discomfort based representative concentration pathways (RCP) scenarios in coming decades using temperature-humidity index (THI) and effective temperature (ET): a case study in a semi-arid climate of Iran

The main objective of this study is to know the current state of thermal discomfort and its changes in the coming decades in one of the semi-arid climates of Iran. This study is very important considering the importance and direct impact of climate change and global warming on human health and can help adopt preventive policies to face them properly. Thermal discomfort changes were assessed by the temperature-humid index (THI) and effective temperature (ET) in Arak City as a representative of the semi-arid climate of Iran. The modeling was done using the CanESM2 general circulation model. The statistical downscaling model (SDSM) software was used to downscale the model data in the period of 2011 to 2099 with three different scenarios of optimistic (RCP 2.6), intermediate (RCP 4.5), and pessimistic (RCP 8.5). The results showed that based on all three scenarios, the values of THI in January, February, and May in the coming decades will be higher than the base values (1976–2005), which will indicate an increase in thermal discomfort in these months. The pattern of changes based on the ET index was almost similar to the THI except in the optimistic scenario in all periods. In this scenario, there is a slight downward trend from 8.1% in the base period to 1.9%, 4.3%, and 3.7% in the decades 2011 to 2040, 2041 to 2070, and 2071 to 2099, respectively. In general, the increasing temperature in the study area based on all three scenarios will cause major changes in thermal comfort, so that thermal discomfort increases not only in hot seasons, but also in other seasons.