Once in 300-to-600-year event but ongoing conflict and state fragility in country compounded effects
The devastating floods in Libya on September 10 were made 50 times more likely and 50 per cent more intense by human-induced global warming, according to a new study by the World Weather Attribution (WWA) published on September 19, 2023.
At least 4,000 people have died due to the floods. However, there have been conflicting reports on the death toll from the United Nations Office for the Coordination of Humanitarian Affairs. The toll can rise further.
WWA is a global consortium of climate scientists who study the role played by human-induced global warming and the consequential climate change in the occurrence, frequency and intensity of extreme weather events such as heatwaves, droughts, cold spells, extreme rainfall, floods and storms.
The study authors defined separate rainfall events to study their return times and the impacts of climate change on them. Return time is the period in which such a rainfall event could reoccur.
A 24-hour event was considered for Spain and Libya, while four-day events were considered for the rest of the European countries.
The scientists concluded that the extreme rainfall event in Spain was a once in 10 to 40 years event. For central Greece, where over 75,000 hectares of agricultural land were inundated by the rains, the event was a once in 80 to 250 years occurrence.
The Libyan floods were caused by a rare medicane, Daniel, which also precipitated floods in other countries of the Mediterranean, such as Greece, Turkiye and Bulgaria from September 4, 2023 to September 7, 2023.
Medicanes are hurricane like tropical storms in the Mediterranean Sea that are becoming more common due to the changing climate.
For Libya, where the rains led to large-scale destruction in the city of Derna, the magnitude of the event was far outside that of previously recorded events. For the country as a whole, it was a once in 300 to 600 years event.
“Ongoing conflict and state fragility in Libya compounded the effects of the flooding, contributing to a lack of maintenance and deterioration of dam infrastructure over time and increasing people’s risk and the resulting impacts,” said the study.
The conflict also limited nation-wide adaptation planning and coordination across a range of climate issues facing the country, such as water scarcity and extreme weather including heat and floods, the authors added.
The floods in Greece, Turkiye and Bulgaria that killed 28 people were made 10 times more likely and 40 percent more intense as compared to a 1.2 degrees Celsius cooler climate, according to the study. The rainfall in Greece was a record breaking 760 millimetres over the period.
A separate low pressure system that got cut off from the northern hemisphere jet stream caused the floods in Spain on September 3, 2023. Torrential rainfall over a few hours caused the floods in Madrid, Toledo, Cadiz and Castello, killing four people.
Both rain-causing systems were connected by an abnormal high pressure area over the Netherlands, associated with an Omega atmospheric blocking event, as per the study.
Such an event occurs when a high pressure system gets trapped between one or two low pressure systems and persists for a long time, leading to extreme weather events such as storms, floods and heatwaves. The same event also lead to heatwaves in France and the United Kingdom in the first week of September.
Omega blocking events have also been linked to other extreme weather events in the past, including the Pakistan floods in 2011, extreme rainfall in northwestern Iran in 2008 and the 2019 heatwaves during May in France and July in Germany. Such events are currently quite difficult to predict.
In Libya, an advisory was issued by the National Meteorological Centre three days before the storm hit. But the exact “impact of that potential rainfall on infrastructure and people was not clearly understood in advance. Further, it is not clear to what extent forecasts and warnings were communicated and received by the general public, or relevant emergency responders,” said the study.
“The extreme rainfall amounts that affected central Greece and their devastating effects are a breaking point in the way we should re-organise the early warning systems towards impact-based alerts, the Civil Protection response capacity and the design of resilient infrastructures in the era of climate change,” said Vassiliki Kotroni, Research Director at the National Observatory of Athens.
“The Mediterranean is a hotspot of climate change-fuelled hazards. After a summer of devastating heatwaves and wildfires with a very clear climate change fingerprint, quantifying the contribution of global warming to these floods proved more challenging,” said Friederike Otto, Senior Lecturer in Climate Science at Grantham Institute — Climate Change and the Environment, Imperial College London.
“But there is absolutely no doubt that reducing vulnerability and increasing resilience to all types of extreme weather is paramount for saving lives in the future,” she added.
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