After Storm Daniel, Mediterranean cities 'need to prepare' flood defences

More than 5,000 people have been killed and many thousands more are missing in Libya after torrential rains hit the north-eastern part of the country on Sunday.

In the space of 24 hours, there was more than 400mm of rain as a result of Storm Daniel, which left behind scenes reminiscent of a post-apocalyptic nightmare after two dams on the approach to the port city of Derna burst.

The storm also caused several days of extreme rainfall in Greece, leading to devastation and numerous deaths, with parts of the country receiving more than a year and a half of rain – about 750mm – in a day. Bulgaria and Turkey were also hit.

As the world’s climate warms, can we expect more of these types of events – and, if so, what can be done to reduce the consequences?

Why was the rainfall and the destruction it caused so extreme?

As it travelled towards Libya, Storm Daniel is said by the World Meteorological Organisation to have taken on the characteristics of a Medicane or Mediterranean hurricane. According to the WMO, such weather events combine elements of a mid-latitude storm and a tropical cyclone.

Prof Jos Lelieveld, who conducts climate change research covering the Mediterranean and the Middle East at the Max Planck Institute for Chemistry in Germany and The Cyprus Institute, said that the extreme heat of the Mediterranean had increased evaporation and this is probably what made the rainfall more severe.

“These things haven’t happened before,” he said. “The conclusion that it has some influence from climate change is almost obvious.”

In Libya, factors such as the breaking of the dams made the destruction far worse, while continued population growth and urbanisation may also have inflated the death toll.

In Greece, by contrast, many of the areas hit in the region of Thessaly were agricultural.

What can we expect in future as the climate continues to warm?

In a study published in Scientific Reports in 2020, Hossein Tabari, a researcher at KU Leuven, a university in Belgium, said extreme precipitation was “expected to intensify with global warming over large parts of the globe”.

While factors such as changes to circulation patterns may intensify or weaken this effect in particular parts of the world, the overall direction of travel, when it comes to extreme rainfall, is upwards.

For example, research published earlier this year indicated that under a high greenhouse gas emissions scenario, extreme rain events, where more than 20mm falls in an hour, could happen more than four times as often in the UK by 2080 as they did in the 1980s.

“Extreme years with record-breaking events may be followed by multiple decades with no new local rainfall records. The tendency for extreme years to cluster poses key challenges for communities trying to adapt,” the researchers wrote in Nature Communications.

How can cities protect themselves from extreme rainfall?

Typically cities are, in Prof Lelieveld’s words, “completely plastered with asphalt and concrete”, leaving floodwater with nowhere to go.

However, he highlights some urban centres that have made considerable efforts to ensure that they are better able to cope with heavy rainfall.

A notable example is the Dutch city of Rotterdam, where the Benthemplein water square, a tiered area, takes in water from nearby paved areas and roofs before releasing it into a nearby canal and the ground.

Prof Lelieveld said that the 2021 European floods, which killed more than 200 people in countries such as Germany and Belgium, showed the importance of taking measures to protect urban areas.

“The water needs to go somewhere so it doesn’t so strongly affect the towns and cities,” he said.

River management is also important, Prof Lelieveld said, with the way that rivers are often canalised and their floodplains built upon causing areas to become more at risk in the event of flooding.

“These areas should be able to be flooded when the river carries a lot of water,” he said.

While he said that in northern Europe, a lot of planning to reduce flooding had taken place, this has tended not to be the case in southern Europe, the Middle East and North Africa.

“Now, maybe, it’s a good time to consider becoming more resilient to weather extremes,” he said.