Researchers say improved forecasting could protect millions in tropical and subtropical regions as climate change intensifies risk.
Scientists may have found a breakthrough in forecasting humid heatwaves a growing and dangerous threat in tropical regions by revealing how recent rainfall and soil moisture can signal when such deadly conditions might arise.
In a first-of-its-kind study experts from the University of Leeds and the UK Centre for Ecology and Hydrology have identified clear links between rainfall patterns and the onset of extreme humid heat across the global tropics and subtropics. The findings, published on Tuesday, April 29 in Nature Communications, could pave the way for early warning systems that help protect vulnerable communities.
a deadly but poorly understood danger
Unlike dry heatwaves humid heatwaves are less studied but more dangerous. When humidity is high, the human body cannot cool itself effectively through sweating, risking severe heat stress. At a wet-bulb temperature of 35°C where heat and humidity combine to block natural cooling people can quickly suffer confusion, organ failure, or even death if not treated immediately.
Some parts of the world, particularly subtropical coastal areas, have already crossed this critical threshold. As global temperatures rise, the frequency and intensity of humid heatwaves are also increasing, putting outdoor workers, the elderly, and low-income communities at greater risk.
New data reveals a trigger mechanism
Led by Professor Cathryn Birch and Dr Lawrence Jackson, the research team examined weather and satellite data from 2001 to 2022, focusing on how rainfall interacts with soil conditions to trigger humid heat.
Their findings revealed an important regional difference:
In drier regions, humid heatwaves tend to occur during or soon after rainfall, as increased moisture fuels humidity.
In wetter regions, these heatwaves more often follow two or more dry days, which allow the land to heat up under clearer skies.
These insights offer a crucial advance in understanding the short-term meteorological drivers of humid heat and highlight how satellite-based soil moisture and rainfall data can be used for near real-time forecasting.
urgent need for early warning systems
“Humid heatwaves can be lethal at temperatures that would be safe under dry conditions,” said Professor Birch. “The tropics are already humid. Even a small increase in global temperature makes these events far more dangerous.”
Co-author Professor John Marsham added that future work could involve analyzing conditions on hourly timescales, potentially enabling real-time alerts for at-risk populations.
The research reinforces the need to urgently cut greenhouse gas emissions while also investing in forecasting tools that can help communities prepare for and respond to increasingly deadly climate extremes.