Climate change brings wetter thunderstorms, experts say

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Due to global warming, thunderstorm clouds increasingly carry more moisture and pile up higher, climate researcher Marc Olefs from Geosphere Austria told APA at a natural hazards conference in Vienna. According to Olefs, the dangers continue to increase as the climate crisis progresses. Therefore, protective structures and the flow of information between authorities, emergency services and those affected must be improved. According to Olefs, intact forests also reduce the risk of damage.

Warm air can absorb seven percent more moisture per additional degree Celsius if the conditions for such saturation are met, according to Olefs, who works in the Climate Research Department. Currently, global warming in Austria is greater than two degrees Celsius. As a result, according to the calculations, a cloud can store around 15 percent more water than before. “We can actually see in our measurement data that the intensity of extreme hourly precipitation has increased by 15 percent in recent decades,” he said.

“At the same time, global warming is making the air stratification more unstable,” said the expert: “As a result, thunderstorms are becoming higher and short-term extreme precipitation is increasing.” According to Austrian measurement data, days with extreme precipitation have become more frequent over the past 60 years, while days with low precipitation have become rarer. This trend would “almost certainly” continue due to global warming.

With global warming of three degrees Celsius, which is to be expected at the end of the century with the current climate protection measures, global warming in Austria would amount to around five degrees Celsius, according to Olefs: “This means that we can expect around three degrees more.” This would increase the potential intensity of precipitation by up to 25 percent. “Our calculations also show that the number of days with severe weather potential, i.e., hail, squalls and thunderstorms, will increase by up to 30 percent compared to the current situation,” he reported.
The weather forecasts had worked very well with the current heavy rainfall in Austria and southern Germany, said Olefs: “The warnings were already with the relevant authorities before the first drop fell, so to speak.” However, much work is still being done on the information chain so that everyone involved is warned in good time and can take protective measures.

According to Olefs, there is a “real need to catch up” in terms of protective structures such as retention basins, mobile flood protection, and hazard zone planning. They would have to adapt to the increasing dangers across the board. Experts from Geosphere Austria, Torrent and Avalanche Control recently proved that more and better protective structures reduce the risk of local flooding and damaging events. He reported: “It is also very clear from a scientific point of view that we need to increase the water absorption capacity of the soil again.” This means that the sealed soil area should be reduced, not increased.

An intact forest also mitigates the effects of extreme precipitation, explained Jan-Thomas Fischer from the Department of Natural Hazards at the Federal Research Center for Forests (BFW). Firstly, as an “object protection forest, ” it directly protects houses, towns, roads and railroad tracks from the consequences of landslides and mudslides. It can also absorb more water than open areas during heavy rainfall, potentially preventing flash flooding. It therefore fulfils a “site protection” function.

Of course, a forest can only achieve all of this if it is not damaged on too large a scale by disturbances such as drought, beetle infestation, windthrow and snow breakage, or decimated by forest fires such as the one on the Rax in Lower Austria in 2021, says Fischer. However, this is increasingly to be feared due to the climate crisis. “There is, therefore, a lot of research into what a climate-fit forest should look like locally,” he said. The information on “which forest belongs where” would then be passed on to forest managers, for example, with a BWF “tree species traffic light” to assess suitable trees.

At the “Interpraevent 2024” conference, international experts will meet in Vienna from June 10 to 13, 2024, to exchange research findings and discuss how to “manage” the risks of natural hazards in the climate crisis.