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Researchers have discovered a method to enhance warning systems aimed at protecting communities that are increasingly threatened by humid heatwaves. These events, which are becoming more prevalent due to climate change, pose serious risks to human health.
A team from the University of Leeds and the UK Centre for Ecology and Hydrology has conducted a pioneering analysis on how recent rainfall patterns interact with varying land conditions—whether dry or moist—to affect the likelihood of extreme humid heat in tropical and subtropical regions.
This study, published in the journal Nature Communications, provides groundbreaking insights that could pave the way for the establishment of early warning systems targeting vulnerable populations in these areas.
As climate change progresses, the danger posed by humid heatwaves rises, particularly in tropical climates. While considerable research has focused on dry heatwaves, the atmospheric dynamics that lead to extreme humid heat remain less understood.
Humid heat is directly related to heat stress, occurring when environmental conditions exceed the body’s capability to cool itself. Severe instances can elevate core body temperatures by 3°C or more, leading to symptoms such as confusion, seizures, and unconsciousness. Without immediate intervention, severe heat stress can result in muscle damage, major organ failure, or death.
Arguably, the most alarming aspect of humid heat is that a wet-bulb temperature of 35°C means individuals cannot effectively cool down through sweating. Certain subtropical coastal regions have begun to reach this critical temperature.
Dr. Lawrence Jackson, the lead author of the study and a Research Fellow in the School of Earth and Environment, emphasized, “As climate change continues to drive more frequent and severe humid heat events, particularly in tropical and subtropical regions, the risks to vulnerable groups and outdoor workers are escalating.”
“Our research offers valuable insights that could lead to improved early warning systems for humid heat, utilizing near-real-time satellite data on soil moisture and rainfall,” he added.
The research team analyzed data on humid heatwaves spanning from 2001 to 2022, focusing on how recent rainfall impacted the occurrence of these events. They employed satellite observations to differentiate between days with wet and dry conditions and assessed how these variations in rainfall influenced heatwave likelihood.
Humid heatwaves are prevalent in various global regions, including monsoon areas like West Africa, India, East China, and northern Australia, as well as humid zones such as the Amazon, southeastern United States, and Congo basin, and in hot coastal areas of the Middle East.
The findings underscore that recent rainfall significantly influences the onset of humid heatwaves, indicating that the likelihood of such events varies based on whether the environment has been dry or wet.
In regions experiencing drier conditions, humid heatwaves are more likely to occur during or shortly after periods of increased rainfall. Conversely, in wetter areas, these heatwaves are generally preceded by at least two days of reduced rainfall.
This phenomenon occurs because rainfall enriches soil moisture, thereby increasing local humidity. Alternatively, less rainfall allows the land surface to heat up, raising temperatures.
Cathryn Birch, a Professor in Meteorology and Climate, led the study and noted, “The situation regarding tropical humid heat is truly alarming. Humans typically cool down through sweating; however, elevated humidity diminishes this process.”
“Humid heatwaves can be lethal at air temperatures that would be considered safe under dry conditions. The inherently humid nature of tropical climates means that even minor increases in global temperatures can trigger significant surges in dangerous humid heat extremes. It is critical to both reduce greenhouse gas emissions urgently and develop advanced early warning systems for humid heat,” she remarked.
Co-author John Marsham, a Professor of Atmospheric Science, suggested, “Our findings focus on broader trends, but a logical next step would involve analyzing data on an hourly basis. This approach could facilitate near-real-time predictions, which would greatly benefit vulnerable communities.”
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