Background: This study assessed the applicability of the Environmental Stress Index (ESI) as an alternative to the Wet Bulb Globe Temperature (WBGT) for evaluating outdoor heat stress in Iran’s climates.
Methods: Using summertime meteorological data from 1992 to 2021, including relative humidity, temperature extremes, and solar radiation, the research analyzed nine representative cities with varying climates. Data were sourced from the National Meteorological Organization, and projections used the Hadley Coupled Atmosphere-Ocean General Circulation Model (HadCM3) and the Long Ashton Research Station Weather Generator (LARS-WG) models, extending predictions to 2099.
Results: The classification of cities revealed temperature fluctuations (29.91-46.00°C) and relative humidity variations (32.33%-72.15%), emphasizing substantial climatic disparities. An intra-class correlation (ICC) analysis of ESI and WBGT showed strong agreement (ICC>0.9) in seven cities, validating the reliability of both indices. However, lower ICC values in Ahvaz and Bandar Abbas suggest local climatic factors such as humidity and heat may influence index performance. Both indices peak in July, with Ahvaz projected to have the highest values by 2099, reinforcing future heat stress concerns.
Conclusion: Given these limitations, this study emphasizes the need to incorporate additional environmental parameters, such as wind speed, land surface temperature, and air pollution, to improve heat stress assessments. The findings support ESI as a reliable metric for environmental stress evaluation, offering a practical alternative to WBGT across Iran’s climate. Its applicability in future climate projections highlights its potential to shape proactive public health strategies mitigating rising heat-related risks, especially in regions facing extreme conditions.