Heat Stress in Iranian Cities (1992-2022): A Spatiotemporal Analysis of WBGT and UTCI indices

Abstract

Background: Climate change is accelerating heat stress globally, especially in Iran’s arid and semi-arid regions, threatening public and occupational health. Since air temperature alone poorly reflects physiological stress, this study used the Wet-Bulb Globe Temperature (WBGT) and the Universal Thermal Climate Index (UTCI) to examine long-term spatiotemporal trends across ten diverse Iranian cities.

Methods: Using daily meteorological data from the Global Surface Summary of the Day (GSOD), we calculated WBGT using the Liljegren model and UTCI using the UTCI-Fiala model. Descriptive statistics and linear regression analyses were conducted in Microsoft Excel to assess annual trends in average and maximum WBGT and UTCI values.

Results: The analysis revealed clear spatial and temporal variations in WBGT and UTCI across Iranian cities from 1992 to 2023. Southern cities such as Bandar Abbas and Ahvaz recorded the highest average WBGT (23.46°C and 19.46°C) and UTCI (28.61°C and 25.84°C), with Ahvaz showing the highest maximum UTCI (51.68°C). Significant upward trends in both average and maximum WBGT and UTCI were observed in most cities (p < 0.001), particularly in Ahvaz (WBGT slope = 0.50, UTCI slope = 0.75). These findings indicate intensifying chronic and extreme heat stress across diverse climatic zones in Iran.

Conclusion: This study found rising WBGT and UTCI trends across Iranian cities, indicating growing heat stress risks. Southern cities face extreme conditions, but increases are nationwide, highlighting the urgent need for heat adaptation strategies in public health policies, occupational safety regulations, and urban planning.