Thermal Profile of Iran in Summer Season using Thermo-hygrometric Index (THI)

Background and Aim: The thermo-hygrometric index (THI) represents the combined effects of two quantities of air temperature and relative humidity on living organisms and the occurrence of environmental stress, which is expected to change in the coming decades due to the consequences of global warming. Therefore, this study aims to analyze the thermal image of Iran using THI in the summer season of Iran during a statistical period of 30 years. Materials and Methods: The data related to the average of two variables of air temperature (Celsius) and relative humidity (percentage) daily from 60 synoptic meteorological stations for a statistical period of 30 years (1985-2014) from the summer season of Iran were obtained from the Iranian Meteorological Organization. The THI was calculated for the summer season. The Mann-Kendall statistical test was used to investigate the changes in air temperature, relative humidity and THI. Results: The trend of temperature parameter changes for the summer season has been increasing in 88.38 percent of Iranian cities, and this increasing trend has been statistically significant in 66.03 percent of these monitored stations. Considering the Sens slope, the most significant increase in the temperature parameter was seen at Yasouj station (+1.050 °C/decade). The trend of changes in temperature-humidity index has been increasing in 75% of the cities, and this increasing trend has been statistically significant in 71.43% of these stations. The most significant increase in THI was seen at Qaemshahr station (+0.449°C/decade). Also, the trend of changes in relative humidity has decreased in 88.3% of cities, and this decreasing trend has been statistically significant in 58.5% of these stations. The most significant decrease in relative humidity was seen in Zabul station (-5.700 °C/decade). Conclusion: For a statistical period of 30 years in Iran, in the summer season, the trend of changes in THI has been generally increasing and the trend of changes in relative humidity has been decreasing. Considering the phenomenon of climate change and global warming, heat stress evaluation using the THI seems necessary for the general awareness of people and the adoption of prevention policies in the country.