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Summer 2022: Island exposed by lack of water in the Sylvenstein reservoir in Bavaria

Photo: Peter Kneffel / dpa

Due to climate change, weather extremes are occurring more frequently. Heat waves will become more frequent, as will droughts and extreme rain and storms. But what if several extremes increase in a region at the same time?

Overall, Earth's land masses are getting wetter as global temperature rises, a study shows. In addition, according to the model calculations, the probability of heavy precipitation and extreme heat will increase simultaneously in some regions by the end of the century, which increases the risk of flooding. An increased probability of drought and heat is less likely to occur in the same area, but there are regional differences.

According to the analysis, large parts of Europe – including Germany – South and North Africa as well as the Amazon region in South America will increasingly experience drought and heat from 2050 to the end of the century. Heat exacerbates the problem of low precipitation because higher temperatures cause more water to evaporate. The risk of extreme droughts is increasing.

The eastern United States, East and South Asia, Australia and Central Africa, on the other hand, will experience more wet and hot extremes. The problem is that while heat and drought are not the same thing, high temperatures can help soils dry out. They then absorb water more poorly. Subsequent rain thus leads more easily to floods and landslides. The study was published in the journal Earth's Future.

Catastrophes like those in the Ahr Valley

"Compound climate extremes have attracted significant attention in recent decades as they place a disproportionate burden on agriculture, industry and ecosystems – much more than individual extreme events," said Haijiang Wu, a researcher at Northwest A&F University in China and lead author of the study, according to a statement on the study. Wu's team has brought together a number of climate models and predicted composite climate extremes by the end of the century – assuming that carbon dioxide emissions continue to rise.

Although, according to the analysis, the risk of dry-hot extremes is increasing in Germany, the country was also confronted with the consequences of wet and hot conditions in 2021: At that time, high temperatures dried out the soils in the already low-rainfall summer. Shortly thereafter, heavy rains poured over the parched land. Flash floods and violent landslides occurred in the Ahr valley. More than 100 people died, houses were washed away.

In the regions that, according to the analysis, are likely to be particularly affected by hot and wet extremes in the future, there are many densely populated areas that are already vulnerable to geological hazards such as landslides and mudslides and where a large part of the world's crops are grown, according to the statement on the study. An increase in heavy rainfall and heat waves could lead to more landslides that threaten local infrastructure, while floods and extreme heat could destroy crops.

The fact that the earth is getting wetter overall can be explained physically: With every degree Celsius temperature increase, the atmosphere can store six to seven percent more water – which later rains down somewhere.

"Given that the risk of compound hot/humid extremes in a warming climate is greater than that of compound dry-hot extremes, these hot/humid extremes should be included in risk management strategies," Wu said.