Objectives Climate change affects a wide range of issues, including work productivity due to elevated temperatures. This is particularly important for agricultural workers in tropical countries like Thailand. This cross-sectional study aims to investigate the effects of heat stress exposure on productivity among Thai sugarcane workers during harvesting seasons.

Methods This study involved 287 sugarcane workers from Nakhon Sawan Province, Thailand, during the cooler or hotter 2023 harvesting periods. Information was collected on their demographic characteristics, health behaviors, working conditions, and work output (sugarcane stalks harvested). Wet bulb globe temperature (WBGT) was recorded in the fields during 14 cool and 11 hot season days. A full work shift time-weighted average effective WBGT (WBGT_eff-FS-TWA), adjusted for clothing factors, was calculated to provide an estimate of heat stress exposure over a full work shift. Multiple linear regression determined the effects of heat stress exposure on the average number of sugarcane stalks harvested per hour adjusting for available confounders.

Results Recorded WBGT_eff-FS-TWA values averaged 31.3°C [standard deviation (SD) 2.8, range 22.9–35.4°C]. The mean number of stalks harvested per hour was 387, SD 185, with higher rates observed when harvesting burnt sugarcane and working solo. For every 1°C rise in WBGT_eff-FS-TWA above the lowest observed baseline of 22.9°C, the average number of sugarcane stalks harvested decreased by 9 stalks per hour (β -8.59, 95% confidence interval -16.19– -0.99).

Conclusion Increased heat stress exposure decreases overall productivity. As global temperatures rise, heat stress increases, significantly impacting agricultural output alongside worker health.

Key terms agricultural worker; climate change; exposure; harvesting period; heat stress; productivity; productivity loss; sugarcane; Thailand; wet bulb globe temperature.

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