A critical systematic narrative review of the WBGT index for heat stress assessment in diverse climatic regions: insights from Iran

Heat stress is a major occupational hazard in hot environments. This narrative review evaluated the limitations of the Wet Bulb Globe Temperature (WBGT) index across different climatic zones and explored alternative or complementary indices. We searched PubMed, Scopus, Web of Science, and SID for articles published between January 2013 and December 2024 with English and Persian language. Keywords used in the search included “WBGT”, “Wet Bulb Globe Temperature”, “heat stress index”, “occupational exposure”, and “Iran climate” (Boolean combinations). After removing duplicated papers and screening the remained articles by two independent reviewers, 42 papers were included for qualitative synthesis. In arid/dry regions, WBGT tended to underestimate physiological strain (low wet-bulb temperature despite high radiant heat), while in humid coastal areas, it sometimes overestimated the heat strain risk (high wet-bulb temperature but complex interactions with airflow and clothing). Comparative analyses showed UTCI and PHS can improve physiological prediction in specific contexts, but it requires more data and equipment. WBGT remains practical for many workplaces, but country- or climate-specific calibration, integration with physiological monitoring (e.g., heart rate), and hybrid approaches are recommended to improve worker protection.