A recent study led by Cathryn Birch has identified critical connections between rainfall patterns and extreme humid heat in tropical and subtropical regions. The research was led by Dr. Lawrence Jackson, a Postdoctoral Research Fellow in the School of Earth and Environment. As his first step in this Herculean task, he used satellite observations to separate wetter versus drier days. These findings indicate that humid heat waves are increasingly lethal in areas like West Africa, India, East China, and Northern Australia. This pattern has been observed elsewhere in similarly humid regions across the globe, including the Amazon, southeastern United States, and the Congo Basin.
Using weather and climate data from 2001 to 2022, the study modeled the breeding conditions for humid heat waves to better inform the public. All of these events are deeply concerning. In conditions where wet-bulb temperatures exceed 35°C, humans begin to lose their ability to effectively cool themselves through sweating, resulting in lethal heat stress.
Understanding Humid Heat Waves
Humid heat waves, also known as wet bulb heat waves, occur when extreme temperatures and humidity intersect. They are serious health hazards because they obstruct the body’s natural capacity to cool itself. In the tropics, such conditions typically come on the heels of at least two days of suppressed convection.
According to Dr. Jackson, extreme heat stress can increase your core body temperature by at least 3°C. This potentially life-threatening increase can result in severe mental confusion, seizures, or loss of consciousness. The combination of extremely high humidity and temperature creates conditions that are dangerous because the human body can’t cool itself.
“The outlook for tropical humid heat is really concerning. Humans avoid overheating by sweating. Evaporation of the sweat cools your body, allowing you to maintain a safe body temperature. Humidity makes this less effective.” – Cathryn Birch
This new research shows that a number of subtropical coastal sites have already exceeded this dangerous 35°C threshold. This shocking increase has created deadly health burdens for the communities that reside in these neighborhoods.
Impact of Climate Change
Climate change is increasing the frequency and intensity of humid heat events. This disproportionately endangers vulnerable populations and outdoor workers. The research underscores a pressing need for improved early warning systems that utilize near real-time satellite observations for soil moisture and rainfall data.
Dr. Jackson emphasized the importance of this new understanding: “With climate change driving more frequent and intense humid heat events, particularly in tropical and subtropical regions, the risks to vulnerable populations and outdoor workers are increasing.”
Evidence finds that even a modest increase in global temperatures will result in a major increase in life-threatening humid heat extremes in naturally humid regions. This toxic mix further complicates the already difficult work of climate adaptation.
“Humid heat waves can be lethal at air temperatures that for dry heat would be relatively safe. The tropics are naturally humid and even an apparently small increase in global temperatures leads to large increases in dangerous humid heat extremes.” – John Marsham
Future Considerations
The results of this study point to a strong and immediate call to action on several fronts. Reducing greenhouse gas emissions is as urgent as ever to address the increasingly humid heat conditions that climate change is causing. Moreover, the creation and advancement of successful early warning systems would prevent loss of life through timely warnings of dangerous weather events.
As researchers Cathryn Birch and Dr. Jackson argue, we should be taking a proactive approach to solve these challenges. They argue that improved understanding of rainfall patterns and their effects on heat waves can lead to better preparedness strategies for communities at risk.