WASHINGTON – Human-caused climate change doubled the likelihood and intensified the heavy rains that led to devastating flooding in Central Europe earlier this month, a new flash study found.
Torrential rain in mid-September from Storm Boris pummeled a large part of central Europe, including Romania, Poland, Czechia, Austria, Hungary, Slovakia and Germany, and caused widespread damage. The floods killed 24 people, damaged bridges, submerged cars, left towns without power and in need of significant infrastructure repairs.
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The severe four-day rainfall was “by far” the heaviest ever recorded in Central Europe and twice as likely because of warming from the burning of coal, oil and natural gas, World Weather Attribution, a collection of scientists that run rapid climate attribution studies, said Wednesday from Europe. Climate change also made the rains between 7% and 10% more intense, the study found.
“Yet again, these floods highlight the devastating results of fossil fuel-driven warming," said Joyce Kimutai, the study's lead author and a climate researcher at Imperial College, London.
To test the influence of human-caused climate change, the team of scientists analyzed weather data and used climate models to compare how such events have changed since cooler preindustrial times to today. Such models simulate a world without the current 1.3 degrees Celsius (2.3 degrees Fahrenheit) of global warming since preindustrial times, and see how likely a rainfall event that severe would be in such a world.
The study analyzed four-day rainfall events, focusing on the countries that felt severe impacts.
Though the rapid study hasn't been peer-reviewed, it follows scientifically accepted techniques.
“In any climate, you would expect to occasionally see records broken," said Friederike Otto, an Imperial College, London, climate scientist who coordinates the attribution study team. But, “to see records being broken by such large margins, that is really the fingerprint of climate change. And that is only something that we see in a warming world.”
Some of the most severe impacts were felt in the Polish-Czech border region and Austria, mainly in urban areas along major rivers. The study noted that the death toll from this month's flooding was considerably lower than during catastrophic floods in the region in 1997 and 2002. Still, infrastructure and emergency management systems were overwhelmed in many cases and will require billions of euros to fix.
Last week, European Union chief Ursula von der Leyen pledged billions of euros in aid for countries that suffered damage to infrastructure and housing from the floods.
The World Weather Attribution study also warned that in a world with even more warming — specifically 2 degrees Celsius (3.6 degrees Fahrenheit) of warming since preindustrial times, the likelihood of ferocious four-day storms would grow by 50% compared to current levels. Such storms would grow in intensity, too, the authors found.
The heavy rainfall across Central Europe was caused by what's known as a “Vb depression” that forms when cold polar air flows from the north over the Alps and meets warm air from Southern Europe. The study's authors found no observable change in the number of similar Vb depressions since the 1950s.
The World Weather Attribution group launched in 2015 largely due to frustration that it took so long to determine whether climate change was behind an extreme weather event. Studies like theirs, within attribution science, use real-world weather observations and computer modeling to determine the likelihood of a particular happening before and after climate change, and whether global warming affected its intensity.
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This story has corrected the range of increased intensity of rains due to climate change to 7% to 10%, rather than 7% to 20%, based on a data correction issued by World Weather Attribution.
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