The extreme rainfall that contributed to the failure of two dams in Libya earlier this month was probably made substantially more likely and more intense by climate change. There have been close to 4000 confirmed deaths due to the collapse of the dams, with thousands of people still missing.
Storm Daniel caused an inland dam near the coastal city of Derna, which has around 100,000 inhabitants and is situated in the north-east of Libya, to fail overnight on 10 September. A second dam downstream, which was closer to Derna, then also failed, sending a sudden wave of water into the city.
As of 18 September, the World Health Organization had recorded 3958 fatalities from Libya’s floods, with more than 9000 people unaccounted for.
Storm Daniel also brought unprecedented rainfall to parts of Europe. Heavy rain in Spain caused several deaths, while Greece saw a record-breaking 760 millimetres of rain over just four days. The subsequent flooding caused at least 17 deaths and submerged more than 75,000 hectares of agricultural land in the centre of the country.
“This event was a breaking point in Greece,” says Kostas Lagouvardos at the National Observatory of Athens. “From now on, we will speak about what happened before and after Daniel.”
The intensity of the rain was partially driven by a “blocking” pattern in the jet stream that created a slow-moving storm, as well as hot surface temperatures in the Mediterranean Sea, according to a study from World Weather Attribution, a group of researchers who look at links between extreme weather and climate change.
To determine how climate change may have contributed to the rain, the researchers compared observed trends with projections from different climate models, with and without the influence of human-caused warming.
They found human-induced climate change may have increased the intensity of the rainfall seen in Greece, Bulgaria and Turkey by as much as 40 per cent, as well as making such intense rain 10 times more likely to occur. In Libya, they found human-induced climate change may have made the extreme rain as much as 50 times more likely and 50 per cent more intense.
However, due to having limited data on precipitation and using climate models without sufficient resolution to capture local rainfall, the researchers couldn’t rule out the possibility that human-induced climate change didn’t actually make these events more likely or more intense.
But Friederike Otto at Imperial College London says the known link between a warmer atmosphere and more intense rain is enough to assume some contribution of climate change. “It would be really careless to say there was no change.”
Earlier research also found that while climate change is driving a decline in overall precipitation in the Mediterranean, it will lead to more intense extreme events, such as these floods.
In Libya, the effects of the storm’s intensity were also compounded by a lack of early warning and neglected infrastructure following years of political instability.
Manoochehr Shirzaei at Virginia Tech says the dams that failed were built to prevent previous floods and had been effective in the past. “Since people had this false sense of security, they were living just behind this second dam,” he says. “Nobody had time to escape.”
However, the dams were known to be vulnerable. In 2022, civil engineer Abdelwanees Ashoor published a study saying the dams were ill-prepared to manage extreme rain. Built in the 1970s, they were in need of repair, but had been neglected due to civil war and political chaos. A project to repair the dams that began in 2010 was halted after an uprising against former Libyan leader Muammar Gaddafi’s regime.
The torrential rain in Libya, which the researchers have called a 1-in-600-year event, proved too much for the dams. “It dumped so much water, it was larger than what the dams were built for,” says Shirzaei.
Ageing infrastructure is vulnerable to climate extremes in many other parts of the world, says Shirzaei, pointing to US dams that were built more than a century ago and are in need of repair. “This is a global problem,” he says.