Scientists uncover a driving force behind deadly humid heat waves
Heat and humidity are a deadly combination. Scientists believe they’ve uncovered a key that unlocks advanced warnings
Heat waves are an increasing threat for a large swath of the world’s population. Excessive temperatures are bad enough on their own, but adding in humidity is a potentially deadly combination.
Humid heat is already pushing the limits of survivability in some regions, and the problem could get worse as climate change forces temperatures to rise and heat waves to grow more frequent.
Improved warnings about these deadly temperature extremes are a critical step toward staying safe in the future. A team of scientists believe they’ve found an important driver that can help forecasters and officials warn vulnerable populations about impending humid heat waves.
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Humidity is a killer in major heat waves
Sweat lowers our body temperature through evaporative cooling. Water absorbs heat when it converts from liquid to water vapour, drawing heat away from our skin and helping our bodies cool down in the process.
Excessive humidity in the air prevents our sweat from evaporating efficiently, trapping heat and forcing our body temperatures to rise.
A body temperature that rises too high can cause heat exhaustion or heat stroke—a dangerous and potentially life-threatening medical emergency. Given the dangers posed by humid heat, predicting these hazardous weather events is key to saving lives.
Humid heat waves common in the tropics and subtropics
Recent research published in Nature Communications found a critical link between the onset of humid heat waves and rainfall patterns throughout subtropical and tropical regions of the globe.
Certain regions of the world, such as coastal sections of the Persian Gulf and portions of India, are very vulnerable to bouts of humid heat. But it’s a growing concern throughout the tropics and subtropics—including the southeastern U.S. and the Caribbean—and it's a problem that will only get worse with climate change.
Rainfall patterns likely influence humid heat
The team found that humid heat waves are more likely after minor rainfall events in the tropics and equatorial regions, while bouts of excessive heat and humidity are more common after heavy rainfall events in more arid regions.
Why the difference?
Heat waves are often driven by a feedback cycle between the land and the atmosphere. We’re used to drought-induced heat waves across Canada, especially on the Prairies. But, as the researchers found, feedback is also a critical factor in potentially deadly humid heat waves.
Rain and clouds are commonplace in the tropics. The lack of clouds during rain-free spells can heat up the moist ground, allowing excessive heat to build and accompany the region’s already stifling humidity.
Meanwhile, in drier regions such as portions of Australia, higher rainfall totals wet the ground and contribute humidity to an atmosphere that’s already blazing hot under normal circumstances.
“Our findings are a key step towards greater understanding of the meteorological processes underpinning humid heatwaves at the regional scale,” the researchers noted. “Crucially, these findings will inform the design of much-needed early warning systems for humid heat extremes.”
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