Expert comment: Storm Daniel and floods in Libya

Thousands of people in Libya are reported dead after a powerful storm triggered devastating floods, according to BBC News.

Storm Daniel made landfall on Sunday, prompting authorities to declare a state of extreme emergency.

Meteorologists from the University of Reading have explained some of the issues that could have contributed to the disaster. 

Early warning systems

Professor Hannah Cloke, professor of hydrology at the University of Reading, said: “To be effective, flood forecasting systems need good data on forecast rainfall and river levels, a network of well-maintained measuring instruments on the ground, and a clear plan to get people out of harm's way. The tragic death toll in Libya from the catastrophic flooding that has decimated a city shows what can happen if any parts of this chain are not in place or don't work properly. It seems likely that the worst of the flooding has been caused by a dam failure, although it is possible that very sudden, very heavy rain has caused flash floods on their own.

“Libya has far from the ideal economic or political conditions to provide adequate flood early warning systems.”

Dam failure

Professor Liz Stephens, Professor in Climate Risks and Resilience, said: “Much of the devastation from Storm Daniel in eastern Libya appears to be caused by catastrophic flooding from the failure of one or more dams following exceptional rainfall totals. The dams would have held back the water initially, with their failure potentially releasing all the water in one go. The debris caught up in the floodwaters would have added to the destructive power.

"Medicanes such as Storm Daniel are relatively rare, and tend to occur more frequently in the western portion of the Mediterranean Sea than the arid Libyan coastline. It is more difficult to understand the potential for catastrophic extreme events in an arid climate, where even moderate rainfall events are few and far between. This makes it a challenge to design and build resilient infrastructure.”

Storm Daniel 

Professor Suzanne Gray, Professor of Meteorology, said: “Storm Daniel is a long-lived Mediterranean cyclone that has been active for more than a week since it formed as a low-pressure weather system around the 4h September.

“Intense Mediterranean cyclones with hurricane-like characteristics are termed medicanes (i.e. Mediterranean hurricane). These systems can even have the cloudless “eye” visible in satellite imagery that is characteristic of hurricanes.

“Medicanes are relatively rare, about 1-3 per year, but can have devastating impacts on landfall due to their associated flooding, storm surge and strong winds. Their genesis is mostly in the western Mediterranean and in the region extending between the Ionian Sea and the North-African coast.

“Fluxes of heat and moisture from the Mediterranean sea are usually considered to be important in medicane development and these fluxes are enhanced by warm sea surface temperatures.

“Medicane Ianos, one of the most devastating recent medicanes, had peak winds of 86 knots (99 mph) on landfall in Greece in September 2020, equivalent to a category two hurricane. It caused infrastructure damage and four fatalities.

“The IPCC 6th assessment report concludes that there is consistent evidence that the frequency of medicanes decreases with climate warming, but the strongest medicanes become stronger.”

Climate change

Professor Liz Stephens added: “Climate change is thought to be increasing the intensity of the strongest medicanes and we are confident that climate change is supercharging the rainfall associated with such storms. It would be interesting to evaluate whether, like 40 degree temperatures in the UK, the rainfall totals in eastern Libya would have been physically implausible without climate change. However, this is a complex question that would have to take into account any changes in storm track as well as the rainfall totals."