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Catastrophic flooding in Libya was fuelled by a “medicane”, an intense cyclone with hurricane-like characteristics that can stretch over the Mediterranean and Ionian Sea and North African coast, scientists said.
Storm Daniel, which claimed thousands of lives this week when it struck Libya after lashing parts of Greece, Bulgaria and Turkey, caused dams in the port city of Derna to collapse.
Medicanes are relatively rare, occurring once to three times a year, experts said, but can lead to devastating flooding, storm surges and strong winds.
Storm Daniel hits Greece, Turkey and Libya
Temperatures in the eastern Atlantic and eastern Mediterranean are 2-3°C higher than normal, creating storms with particularly intense rainfall.
The region has also experienced a high pressure blocking pattern, which trapped the storm over Greece. When it finally moved, it evolved into a medicane that dumped vast amounts of rain on Libya.
Torrential rains of between 150mm and 240mm caused flash floods in several cities, including Al-Bayda, which recorded the a record 414.1mm over a 24-hour period.
The World Meteorological Organization said that sea surface temperatures off the coast of Libya were above 27.5°C, raising the risk of storms.
“Warmer water does not only fuel those storms in terms of rainfall intensity, it also makes them more ferocious,” said Karsten Haustein, climate scientist and meteorologist at Leipzig University. “The fact that Daniel could form into a medicane . . . is likely a result of warmer sea surface temperatures and hence man-made climate change as well.”
Most medicanes have a radius of 70 to 200km, and retain their tropical characteristics for up to three days. They can travel between 1,000 and 3,000km until they lose contact with the sea surfaces that fuel their energy. While the phenomenon can appear year-round, activity usually peaks between September and January.
Experts said Libya’s infrastructure was clearly overwhelmed by the intense rainfall.
Even if the dam did have a spillway, the water levels may have been too high.
“If you’ve had very heavy rainfall for quite a long period of time, the reservoir will fill up and the spillway will be activated because you want to avoid water overtopping the dam and eroding away the structure, which could lead to a loss in stability,” said Simon Mathias of Durham University. “It is possible that the spillway couldn’t take away the water fast enough.”
The WMO said many casualties could have been avoided if Libya had a better weather service that provided information and warnings. At least 5,500 people are declared dead and 10,000 are missing.
Some academics said that it was too soon to tie the event conclusively to climate change, although rising temperatures raise the likelihood of extreme weather events.
“We should expect the occurrence of extreme events unprecedented in the observational record,” said the University of Bristol’s Lizzie Kendon.
“Storm Daniel is illustrative of the type of devastating flooding event we may expect increasingly in the future, but such events can occur just due to the natural variability of the climate, as they did in the past.”