Wet-hot extremes pose a greater danger than hot and dry weather

When you think of global warming, it would seem that we are moving toward a climate that is hotter and drier with more frequent droughts and fires. However, a new study published by the American Geophysical Union paints a different picture. The experts report that most communities will experience wetter conditions as temperatures rise. 

Wet-hot extremes 

The research suggests that, instead of drought, most communities will encounter heavy rainfall in correlation with excessive heat. This co-occurrence of precipitation and heat extremes is referred to as “wet-hot” conditions.

The research highlights that such conditions will not only become more frequent but also more severe and widespread due to climate change. Surprisingly, wet-hot extremes pose a higher risk than prolonged periods of hot and dry weather.

“These compound climate extremes have attracted considerable attention in recent decades due to their disproportionate pressures on the agricultural, industrial and ecosystems sectors – much more than individual extreme events alone,” said study lead author Haijiang Wu, a researcher at China’s Northwest A&F University.

A two-fold problem

During heat waves, the soil rapidly loses its moisture and becomes parched. As a result, its ability to absorb water diminishes significantly. When rainfall follows this, it struggles to penetrate the arid soil. Instead of being absorbed, the water tends to run off along the surface.

Surface runoff

This inability of soil to absorb rainfall following a heatwave leads to a multitude of issues, including the risk of flooding. As water runs off the surface, there’s a potential for it to accumulate in low-lying areas, leading to widespread inundation.

Landslides 

Furthermore, the chances of landslides escalate, particularly in hilly or mountainous regions. This poses a significant threat to local communities, infrastructure, and natural habitats.

Crop failures 

Surface runoff can also lead to crop failures. With the soil not retaining the required moisture, crops do not get the necessary water they need to thrive, leading to decreased yields.

Heavily populated areas 

According to the results of the study, the regions likely to be hit hard by wet-hot extremes host many heavily populated areas that are already prone to landslides and mudflows, and produce many of the world’s crops. 

Focus of the study

“Compound climate extremes can be disastrous for water-food-energy security. The risk evaluation and quantification of compound climate extremes have emerged as a critical knowledge gap,” wrote the study authors. 

Using a series of climate models, the researchers set out to predict compound climate extremes by the end of the century based on a steady increase in carbon dioxide emissions.

What the researchers discovered 

The analysis revealed that while some regions of the world such as South Africa and the Amazon will become drier as temperatures rise, many regions will become wetter, including the eastern United States, eastern and southern Asia, Australia and central Africa.

The researchers also predict that wet-hot extremes will also cover a larger area and be more severe than dry-hot extremes.

Precipitation extremes 

For every one degree Celsius rise in temperature, the atmosphere’s capacity to hold moisture increases by six to seven percent. Since the hotter atmosphere will hold more moisture, there will be more water available for precipitation.

Many parts of the world are already experiencing wet-hot extremes, such as western Europe. The 2021 floods in Germany and Belgium was one of the deadliest flood events in Europe in the past century, claiming more than 200 lives. 

Record summer heat had dried out the soil and set the stage for this catastrophe. A storm complex that brought heavy rainfall triggered massive landslides and flash floods that washed away entire houses.

Risk management strategies 

“Given the fact that the risk of compound wet-hot extremes in a warming climate is larger than compound dry-hot extremes, these wet-hot extremes should be included in risk management strategies,” said Wu.

“If we overlook the risk of compound wet-hot extremes and fail to take sufficient early warning, the impacts on water-food-energy security would be unimaginable.”

The study is published in AGU journal Earth’s Future.

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