A study in subtropical Hong Kong examined 22 definitions of compound hot-humid extreme events and their impact on mortality. Using data from 1995–2021, researchers found that events defined by specific humidity with seasonally-determined thresholds, particularly Hot_wet and Hot_wet95 were significantly associated with increased mortality risk. Older adults, males, and pneumonia-related deaths showed the greatest vulnerability. Notably, pre-summer events also carried elevated risk, challenging the focus on traditional summer seasons. The findings underscore the urgent need to integrate humidity into heat-health warning systems and adaptation strategies, as climate change drives more frequent compound heat-humidity extremes in coastal cities.

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