With unprecedented extreme heat causing approximately 490,000 heat-related deaths globally each year—45% of fatalities in Asia alone—a PolyU research team addresses the critical gaps in current heatwave measurement indices and provides timely insights for improving public safety.

Temperature and humidity impact on heat stress

A research team led by Professor Weng Qihao, Chair Professor of Geomatics and Artificial Intelligence of the Department of Land Surveying and Geo-Informatics, and Postdoctoral Fellow Dr Pir Mohammad, evaluated six heatwave indices through case studies in Spain, the United States, and India.

Their findings, published in the international journal Nexus, demonstrated that the lethal heat stress index, which combines temperature and humidity measurements, proved more effective compared to other indices in identifying dangerous heatwave days, particularly in low-humidity environments. In sub-tropical regions like Hong Kong, temperatures as low as 28°C can pose serious health risks when combined with high humidity, potentially leading to fatigue, dehydration, or heat stroke. The team suggested that evaluating heat stress in humid conditions is crucial for better understanding the impact of heatwaves on human health, particularly relevant for construction workers and agricultural labourers.

Indoor heat stress poses hidden dangers

Additionally, the study also revealed that most heat-related fatalities occur indoors, yet current indices like the Hong Kong Heat Index rely on outdoor heat mapping data provided by climate services. The gap was particularly concerning in densely populated urban areas, where residents of rooftop houses and subdivided flats face increased risk. They suggest revisiting thresholds to establish new global criteria for defining dangerous heatwave limits, considering varied climatic conditions and human adaptability.

“Understanding the relations between climate, heat stress and health is crucial for formulating targeted adaptation and mitigation strategies,” explained Professor Weng. The team recommended developing a comprehensive heat risk framework and early warning systems, while emphasising the importance of interdisciplinary collaboration among climate scientists, health professionals, policymakers and communities to safeguard public health in a changing climate.

Professor Weng is currently the Associate Director of the Research Institute for Land and Space, Director of the PolyU Research Centre for Artificial Intelligence in Geomatics, and Director of the Jockey Club STEM Lab of Earth Observations at PolyU.