The patterns of precipitation triggered to trigger extreme humid heat under the tropics and subtropics

Scientists believe that they have found a way to improve warning systems for vulnerable communities threatened by waves of wet heat, which increase due to climate change and can be damaging and even fatal to human health.

The team of the University of Leeds and the British Center for Ecology and Hydrology provided the very first analysis of the way in which recent precipitation models can interact with dry or humid terrestrial conditions to influence the risk of extreme humid heat under the tropics and global subtropics.

The study, which is published in Nature communicationsprovides new information that could lead to the development of early alert systems for vulnerable communities in these regions.

Climate change means that wet heat waves are an increasing risk for human and animal health, especially in tropical regions. Although there are research established on dry heat waves, there is little understanding of weather engines of extreme humid heat.

The humid heat is linked to thermal stress, occurring when environmental conditions overwhelm the body’s ability to cool. Severe thermal stress leads to an increase in central body temperature of 3 ° C or more and can cause confusion, convulsions and loss of consciousness. If it is not treated quickly, severe thermal stress can cause muscle damage, failure of major organs and death.

Wet heat waves are particularly worrying for humans because a damp bulb temperature (a temperature measurement that explains the quantity of cooling can occur by evaporation in ideal conditions) of 35 ° C means that they are unable to effectively lose heat by perspiration. Several subtropical coastal locations have already known this 35 ° C threshold.

The main author of the study, Dr. Lawrence Jackson, researcher at the School of Earth and Environment, said: “Climate change leading to more frequent and intense wet heat events, especially in tropical and subtropical regions, risks for vulnerable populations and outdoor workers increase.

“The new understanding provided by our research highlights the potential for improving early alert systems for wet heat, using real -time satellite observations for soil humidity and precipitation.”

The team studied humid heat waves through the tropics and subtropics using weather and climatic data from 2001 to 2022.

The researchers have identified the heat waves events and examined how they were influenced by recent precipitation, using satellite observations to distinguish the damp and drier days. They then calculated the probability that a heat wave will occur after these different precipitation conditions.

Waves of wet heat are widespread through the tropics and global subtropics. They occur in regions of monsoon such as West Africa, India, East China and Northern Australia, in wet regions such as the Amazon, the Southeast of the United States and the Congo basin, and in the hot coastal regions of the Middle East.

The new study reveals that recent precipitation models play an essential role in the triggering of humid heat waves in tropical and subtropical regions, the results showing that the risk of wet heat depends on the fact that the surface environment is drier or more humid.

In dry regions, wet heat waves are more likely during or just after periods of improved precipitation. In more humid regions, wet heat waves tend to follow at least two days of removed precipitation.

This difference occurs because precipitation increases the moisture of the soils, which makes the conditions more humid. On the other hand, less precipitation and less clouds allow the earth to warm up, thus increasing temperatures.

Cathryn Birch, professor of meteorology and climate at the Earth and Environment School, led the study. She explained: “The tropical wet heat prospects are really worrying. Humans avoid overheating by sweating. The evaporation of sweat cools your body, allowing you to maintain a sure body temperature. The humidity makes it less effective.

“Waves of wet heat can be deadly at air temperature which, for dry heat, would be relatively safe. The tropics are naturally humid and even an apparently low increase in global temperatures causes a sharp increase in dangerous humid heat extremes.

The co-author John Marsham, professor of atmospheric sciences at the Earth and Environment School, added: “Our results are concentrated on the daily time scale of these heat waves. An next obvious step would be to extend our analysis to time hours that could allow us to work towards almost real time predictions with all the advantages it would bring to vulnerable communities.”