Investigation of Thermal Comfort Changes Using Summer Simmer Index (SSI): A Case Study in Different Climates of Iran

Mehdi Asghari1, Gholam Abbas Fallah Ghalhari2, Hamidreza Heidari3, *
1 Department of Occupational Health and Safety Engineering, School of Public Health, Arak University of Medical Sciences, Arak, Iran
2 Faculty of Geography and Environmental Sciences, Hakim Sabzevari University, Khorasan-Razavi, Iran
3 Department of Occupational Health and Safety Engineering, School of Public Health, Golestan University of Medical Sciences, Gorgan, Iran

© 2021 Asghari et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Occupational Health and Safety Engineering, School of public Health, Golestan University of Medical Sciences, Gorgan, Iran; Tel: +98 25 37833361; E-mail:



This study aimed to assess the thermal comfort trend using a metrological parameter based on the Summer Simmer Index (SSI), for different climates of Iran between 1985 and 2014.


This is a Time-series study. The new SSI was calculated using metrological data in a 30 year- period for illustrating the changes to the thermal comfort or discomfort level through summer months in different climates of Iran. Mann- Kendall test and Sen's Slope were used to compare the upward or downward trend of the index during this period.


The worst thermal condition was observed in the southern and central regions of the country. A few stations were put in comfort zone (77≤SSI<83°F). The fluctuations of SSI were not considerable during the study period (P<0.001). However, a commonly upward trend was observed, indicating rising temperature. This initial assessment, which can be reported daily along with other atmospheric parameters at meteorological stations, could play a significant role in reducing the heat-related complications among exposed individuals and a basis for taking appropriate protective measures.


Based on the results obtained in this study, which has been investigated in Iran for a long period of time, considering intrinsic features of the SSI index, such as ease of calculation and interpretation and also the possibility of calculating the index using daily reported meteorological data, the use of SSI as a screening index of thermal stress in order to adopt preventive policies in outdoor settings in climates of Iran is recommended.

Keywords: Summer simmer index, Climate, Thermal comfort, Trend, Global warming, Wet bulb globe temperature.