Applicability of air enthalpy for heat stress assessment of outdoor environments in different climates of Iran

The aim of the present study was to determine the applicability of air enthalpy for heat stress assessment of outdoor environments in different climates of Iran. The relationships between the enthalpy index and other heat stress indices such as temperature-humidity index (THI), Humidex, and Wet Bulb Globe Temperature (WBGT) were examined. Summertime atmospheric parameters including temperature (°C), relative humidity (%), and atmospheric pressure (hPa) were obtained from the Iranian Meteorological Organization for the months of June, July, and August during a 30-year period from 1987 to 2017. In this study, the De Martonne climate classification system was used, which has identified six different climate classes. Statistical analyzes were performed using the SPSS software v.23 and the Pearson correlation coefficient and linear regression tests. The highest mean air enthalpy and heat stress indices (THI, Humidex, and WBGT) were found in the arid climate during August. The air enthalpy had a direct and strong relationship with air temperature in all climates, and the strongest correlation between was observed in the semi-humid climate (R = 0.899). A direct correlation was found between the air enthalpy index and relative humidity in all climates except the semi-humid climate, and the highest association was observed in the arid climate (R = 0.747). In addition, direct and strong relationships were found between the air enthalpy and the heat stress indices, the highest correlation belonging to the semi-humid climate. With respect to the direct and strong relationships between air enthalpy and the heat stress indices, the simplicity of air enthalpy calculation, and also the possibility of estimating it using meteorological parameters, the enthalpy index can be used as a suitable alternative screening index for heat stress assessment in outdoors, especially in warm and dry regions.