Comparing existing heat wave indices in identifying dangerous heat wave outdoor conditions

Heat waves are projected to become more intense and severe with global warming, impacting human health and deteriorating urban environments. Thus, understanding dangerous heat wave conditions in different climatic and geographic regions is essential. This study examines the effectiveness of six different temperature-humidity-based heat wave indices in identifying dangerous heat wave outdoor conditions, using recent heat wave events observed in Asia, Europe, and the United States as case studies. The lethal heat stress index performed better in identifying days with dangerous heat wave situations than the other indices in a low-humidity environment due to its ability to counteract the offsetting impact of air dryness. Our results suggest that selecting a heat wave index is crucial for identifying dangerous heat wave situations under different climatic, geographic, and meteorological conditions.