Recent Increases in Exposure to Extreme Humid-Heat Events Disproportionately Affect Populated Regions
Extreme heat research has largely focused on dry-heat, while humid-heat that poses a substantial threat to human-health remains relatively understudied. Using hourly high-resolution ERA5 reanalysis and HadISD station data, we provide the first spatially comprehensive, global-scale characterization of the magnitude, seasonal timing, and frequency of dry- and wet-bulb temperature extremes and their trends. While the peak dry- and humid-heat extreme occurrences often coincide, their timing differs in climatologically wet regions. Since 1979, dry- and humid-heat extremes have become more frequent over most land regions, with the greatest increases in the tropics and Arctic. Humid-heat extremes have increased disproportionately over populated regions (∼5.0 days per-person per-decade) relative to global land-areas (∼3.6 days per-unit-land-area per-decade) and population exposure to humidheat has increased at a faster rate than to dry-heat. Our study highlights the need for a multivariate approach to understand and mitigate future harm from heat stress in a warming world.
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- Geophysical Research Letters
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Plain Language Summary
Combined high temperature and humidity can be more dangerous to humans and wildlife relative to high temperature alone. There are known physiological limits to humid-heat and adverse impacts on human-health and performance can be felt well below those limits. Thus, it is important we understand their climatological characteristics and recent changes. Prior research on heat extremes has largely focused on dry-heat. Using two high-spatial resolution datasets, we provide a global-scale characterization of the magnitude, seasonal timing, and frequency of dry- and humid-heat extremes and their historical trends. While dry- and humid-heat extremes occur at the same time of the year in most regions, their timing differs by multiple months in tropical regions with high rainfall. Over the past four decades, dry- and humid-heat extremes have become more frequent over most land regions, with the greatest increases in the tropics and Arctic. Since 1979, each person, on average, has experienced an increase of approximately five additional extreme humid-heat days per-decade. These increases are concentrated over densely populated regions in the tropics and sub-tropics, where humid-heat levels are already high. Our results emphasize the increasing risk from dangerous heat stress, particularly in vulnerable regions of the world.