Workers engaged in outdoor activities are more vulnerable to heat stress and climate change due to direct exposure to environmental conditions. This study aims to preliminary evaluate the applicability of the Discomfort Index (DI)—an empirical index based on dry-bulb and dew point temperatures—in assessing heat stress in open-air environments across various climatic regions of Iran. We employed the De Martonne climatic classification, encompassing six distinct climates, and selected one representative station for each. Meteorological parameters, including minimum and maximum temperatures (°C) and relative humidity (%), were collected from synoptic stations across these six different climatic regions of Iran (Garmsar, Gorgan, Rasht, Ilam, Qaem Shahr, and Piranshahr) over a 30-year period (1987–2017). Necessary parameters, such as dew point temperature and water vapor pressure (hPa), were calculated using established formulas. Subsequently, the DI and three widely utilized heat stress indices (WBGT, ET, and THI) were computed. Statistical analysis was performed using SPSS software (version 23) and Excel 2013. The highest spring dew point temperature (15.8 ± 2.6 °C) was recorded in Rasht’s very humid climate in May, while the lowest (-1.28 ± 3.3 °C) was in Piranshahr’s humid climate in March. In summer, Gorgan (semi-humid climate) exhibited the highest dew point temperature in August (21.56 ± 1.7 °C), whereas Ilam (Mediterranean climate) recorded the lowest in June (1.95 ± 3.1 °C). The highest mean values of the DI, WBGT, ET, and THI indices during spring and summer were observed in Gorgan’s semi-arid climate in May and August, respectively. Conversely, the lowest values were documented in Piranshahr’s humid climate in March and June. Correlation analyses between the DI and other thermal indices in both spring and summer revealed a direct and significantly high correlation. The highest correlation coefficient for the DI was found in the semi-humid climate (R2 = 0.999), while the lowest was observed in the Mediterranean climate (R2 = 0.934). The strong correlation between the DI and other examined heat stress indices, along with its straightforward calculation method, absence of globe temperature measurement requirements, and estimability through meteorological data, positions it as a valuable tool for assessing thermal stress in open environments. Given its high validity and efficiency, the DI presents a viable alternative to more complex indices. The findings indicate that simpler indices, such as the DI, can enhance the management of thermal conditions and mitigate heat stress risks across various regions.
Asghari et al. (Sun,) studied this question.