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Article | WTW Research Network Newsletter

Storm Daniel: A cautionary tale on the need to maintain infrastructure before it’s too late

By Neil Gunn | October 5, 2023

Storms are not constrained by national boundaries, and as they demonstrate their relentless force, they often leave a lasting mark over the regions they traverse.
Climate|Willis Research Network
Climate Risk and Resilience

A low-pressure storm

On September 4, a low-pressure system formed in the Black Sea, initially impacting Bulgaria before moving on to Greece and Türkiye. The system unleashed torrential rain over the island of Skiathos and the central highlands of Thessaly. In Zagora 1,092mm fell in less than 24 hours, 138% of average annual rainfall for this region. Consequently, critical infrastructure, including main road and rail networks connecting Athens and Thessaloniki, were severely disrupted. The agricultural sector also suffered significant losses, with extensive damage to crops and land due to deposition and erosion, requiring years for recovery.

Even a week after the event, parts of Greece remained flooded, and early damage estimates for the storm in Greece are in the order of €2Bn., sadly 27 people lost their lives in Bulgaria, Greece and Türkiye. In light of this storm and the recent wildfires, the Greek prime minister has offered tax breaks to those who purchase insurance and is considering making such insurance mandatory in future[1].

1,092mm rainfall in less than 24 hours, 138% of average annual rainfall for Zagora

€2Bn early damage estimates for the storm in Greece

Storm Daniel

After moving south and west across the warm waters of the Ionian Sea, picking up heat energy and moisture from the sea as it tracked, it intensified into a Mediterranean cyclone. These storms are known as Medicanes. Generally, they do not have sufficient space and time to accumulate energy to the same extent as tropical storms in bigger ocean basins. However, they have been known to gain strength equivalent to a category two storm and can wreak significant damage. On average there are only one or two such storms per year. Opinions are split, but the IPCC[2] report it likely that the number of storms will decrease but the intensity of the strongest medicanes will increase. On September 5 the Hellenic National Meteorological Service now named Daniel and forecast that it would track toward Malta before turning south and east toward Libya.

Image from Emergency Response Co-ordination Centre (ERCC) showing details of rainfall accumulation, equipment requested and maps of flood location.
Image from Emergency Response Co-ordination Centre (ERCC) showing details of rainfall accumulation, equipment requested and maps of flood location.

Libya’s Battle with Storm Daniel

A state of emergency was declared in eastern Libya on September 9, but the fractured nature of the country led to a breakdown in transmission and messaging of warnings. The storm made landfall near Benghazi on the September 10, chief among the destructive elements of the event was the heavy rainfall. Though the amounts were smaller than experienced in Greece, large areas of the country saw record breaking totals. Al Bayda saw 414mm, 76% of the annual average[3]. While the focus of the event has been in Derna, over 200 are reported to have died in other parts of Libya.

The worst effects of the storm were reserved for the town of Derna. In the 1970s two clay core dams were built in a steep sided canyon, the wadi Derna. They were intended to provide drinking and irrigation water and act as flood storage reservoirs. 11km upstream of the town, the larger Derna dam could contain 18 million m3 and was 70m high. Only 100m upstream of residential areas the 1.5million m3 Mansour dam was 45m high. Damaged by a storm in 1986, allegedly the dams hadn’t been maintained since 2002[4], but inspections had revealed shortcomings in their maintenance. This could in part be put down to the Gaddafi regime, but also to the conflict which has persisted since his death.

18 million m3 and 70m high – Derna dam

1.5 million m3 and 45m high - Mansour dam

The upper dam failed and overwhelmed the lower dam, residents reported hearing the sound of the collapse. Much of the town is built on the historic delta of the wadi Derna. One sixth of the buildings were wiped off the map by a wall of water. Testimony includes references to residents being told to shelter in place. Rescuers are finding bodies in 5th floor apartments. The United Nations Office for the Coordination of Humanitarian Affairs recently estimated that 11,300[5] had perished, with up to another 10,000 still missing. Recovery will be hard as roads and bridges have been damaged or closed by flooding and landslides. Though slow to start, no doubt complicated by security concerns and damaged ports and communications, aid is starting to arrive.

Lessons for the Future

Natural disasters are often man-made, and the tale of Derna is all the more poignant because it was a disaster waiting to happen. This is what can happen when a society is complacent and doesn’t heed warnings. All of our societies are dependent on engineered infrastructure which requires inspection and maintenance. A great deal of global infrastructure is at or beyond its design life. In terms of governance some societies are more stressed than others, perhaps by conflict, but this is a demanding era for all nations. Most governments have also made difficult choices over expenditure since the banking crisis of 2007 – 08. When these behaviours are combined with events which exceed the design criteria of structures because of enhanced loading driven by climate change, there may be more tough times ahead. Or opportunities to prevent disasters. It all depends on whether we heed the warnings.


  1. Greek PM vows for a restart after criticism for natural disasters' handling. Return to article
  2. Ali, E., W. Cramer, J. Carnicer, E. Georgopoulou, N.J.M. Hilmi, G. Le Cozannet, and P. Lionello, 2022: Cross-Chapter Paper 4: Mediterranean Region. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge. Return to article
  3. Storm Daniel leads extreme rain and floods Mediterranean heavy loss of life Libya. Return to article
  4. Death toll from floods reaches 11,300 in Libya's coastal city of Derna. Return to article
  5. Libya floods: Conflicting death tolls, Greek aid workers die in crash. Return to article

Head of Flood & Water Management
WTW Research Network
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