The devastating storm that dumped torrential rain along the Libyan coast this month was up to 50 times more likely and 50% more intense due to human-caused climate change, according to an analysis published Tuesday.
Before crossing the Mediterranean, the storm raged for four days and caused extensive damage in central Greece and parts of Bulgaria and Turkey, a region where such extreme storms are up to 10 times more likely and up to 40% more likely. intense due to climate change. the scientists said.
Daylong heavy rains from Mediterranean Storm Daniel caused massive flooding in eastern Libya that overwhelmed two dams, sending a wall of water through the coastal city of Derna that destroyed entire neighborhoods and swept away bridges, cars and people at sea. The death toll has varied, with government officials and aid agencies giving counts ranging from around 4,000 to 11,000 deaths.
The analysis was conducted by the World Weather Attribution group, which aims to rapidly assess the possible role of climate change in extreme weather events.
It is also recognized that the impacts of the storms have been exacerbated by other factors such as deforestation and urbanization in Greece which have changed the landscape and exposed more people to floods, and by conflicts in Libya which have likely led to lack of maintenance of dams and communications. failures. Furthermore, they say, the dams may not have been designed to withstand such extreme rainfall.
“Through these events, we are already seeing how climate change and human factors can combine to create a combined and cascading impact,” said Maja Vahlberg of the Red Cross and Red Crescent Climate Center in the Netherlands and one of 13 researchers who collaborated on the analysis.
The researchers looked at one-day annual maximum rainfall in a region above Libya, calculating this month’s storm to be a once-in-300-600-year event in today’s climate. They also looked at the four-day maximum rainfall in the summer season over a region including Greece, Bulgaria and Turkey, finding that the recent deluge is expected to occur once every five to 10 years.
To assess the role of climate change, the researchers then combined observations of precipitation and climate models to determine whether there had been changes in the probability and intensity of maximum precipitation.
The researchers acknowledged that there was high uncertainty in their estimates, and the data includes the possibility that warming played no role because climate models failed to accurately capture very intense heavy rainfall events.
But they gave equal weight to their observations and climate models, and said they were confident in their findings because it is well-established physics that warming causes the atmosphere to hold more water vapor — about 7% more per every degree Celsius of warming – and nothing else happened to counteract that effect.
“It would be really imprudent to say there has been no change (based on the models),” because of what they know from physics about the effects of warming on precipitation intensity in low-pressure systems, said Friederike Otto, a scientist from the University of Washington. Grantham Institute at Imperial College London.
Climate scientist Michael Diamond of Florida State University, who was not involved in the study, said he didn’t disagree that a warmer atmosphere likely contributed. But he said the analysis differs from most traditional climate studies that start with the basic assumption that global warming is not changing extreme precipitation, and then determine whether that is right or wrong.
Even so, the attribution analysis approach is useful for those who need to take action on climate change, including deciding how to build infrastructure that will be in place for decades to come, he said. If that’s the case, it’s logical to assume that the storms will get worse, “because that’s probably what will happen based on fundamental physics that a warmer atmosphere can hold more water vapor… (and) we need to be prepared.”
University of Pennsylvania climate scientist Michael Mann, who was not involved in the analysis, said such weather attribution studies are somewhat useful but do not capture all the ways climate change affects weather events . Notably, the models used in the analyzes do not account for the fact that, as the poles warm faster than the subtropics, the jet stream is locking into a stationary wavy pattern associated with persistent extreme weather.
“For this reason, my belief is that these attribution studies actually underestimate the impact that human-caused climate change is having on these events,” Mann said in an email.
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