Climate change and other human factors worsened flooding disasters in Libya and Greece

Human-caused warming made the heavy rainfall up to 10 times more likely in Greece, Bulgaria and Türkiye and up to 50 times more likely in Libya, with building in flood plains, poor dam maintenance and other local factors turning the extreme weather into a humanitarian disaster

 

Heavy rainfall, which caused devastation in large parts of the Mediterranean in early September, was made more likely to happen by climate change resulting from greenhouse gas emissions, according to rapid analysis by an international team of climate scientists from the World Weather Attribution group.

 

The study also found that the destruction caused by the heavy rain was much greater due to factors that included construction in flood-prone areas, deforestation, and the consequences of the conflict in Libya.

 

“The Mediterranean is a hotspot of climate change-fueled 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. 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,” said Friederike Otto, Senior Lecturer in Climate Science at Grantham Institute - Climate Change and the Environment, Imperial College London.

 

In early September, a cut-off low which affected Spain and a low-pressure system named Storm Daniel, which formed in the Eastern Mediterranean, brought large amounts of rain over a 10-day period to several countries, including Spain, Greece, Bulgaria, Türkiye and Libya. The heavy rain led to massive floods across the region, killing four people in Bulgaria, five in Spain, seven in Türkiye, and 17 in Greece. The greatest disaster occurred in Libya, where the floods caused the collapse of two dams. While the exact number of casualties is still not clear, there are currently 3,958 confirmed deaths in Derna alone and 170 people elsewhere in Libya, with over 10,000 people still missing.

 

To quantify the effect of climate change on the heavy rain in the region, scientists analysed climate data and computer model simulations to compare the climate as it is today, after about 1.2°C of global warming since the late 1800s, with the climate of the past, following peer-reviewed methods.

 

The scientists divided their analysis in three regions: Libya, where the analysis focused on the northeast part of the country, where most of the rainfall fell; Greece, Bulgaria and Türkiye, where the analysis looked at maximum rainfall over four consecutive days; and Spain, where most of the rain fell in just a few hours.

 

For Libya, the scientists found that human-caused climate change made the event up to 50 times more likely to happen, with up to 50% more rain during the period, as a result of human-caused greenhouse gas emissions. The event is still extremely unusual, and can only be expected to occur around once in 300-600 years, in the current climate.

 

For Greece, Bulgaria and Türkiye, the analysis showed that climate change made the heavy rain up to 10 times more likely to happen, with up to 40% more rain, as a result of human activities that have warmed the planet.

 

For this large region, which encompasses parts of the three countries, the event is now reasonably common, and can be expected about once every 10 years, meaning it has a 10% chance of happening each year. For central Greece, where most of the impacts took place, the event is less probable and only expected to happen once every 80-100 years, equivalent to a 1-1.25% chance of happening each year.

 

“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,” noted Vassiliki Kotroni, Research Director at the National Observatory of Athens.

 

In Spain, where most of the rain fell in just a few hours, the scientists estimated that such heavy rainfall is expected once every 40 years, but they could not conduct a full attribution analysis as the available climate models poorly represent heavy rainfall on timescales shorter than a day.

 

These findings have large mathematical uncertainties, as the events occurred over relatively small areas, and most climate models do not represent rainfall on these small scales well.

 

While the scientists cannot completely rule out the possibility that climate change has not affected the likelihood and intensity of events like these, they are confident that it did play a role for several reasons: increased temperatures generally lead to heavier rainfall and studies project heavier rain in the region as temperatures rise; they could find no evidence of factors that might be making heavy rain less likely and balancing the influence of climate change; and weather station data in the region shows a trend towards heavier rain. Because of the limits in the models, the scientists did not give a central estimate of the influence of climate change, as they have done in previous studies, instead giving an upper-bound of the effect.

 

A key finding of the study is that the very large impacts observed in some of the regions were caused by a combination of high vulnerability of the population and their exposure to the event. In the affected area in Central Greece, most of the cities and communities and a large part of the infrastructure are located in flood-prone areas. In Libya, a combination of several factors including long-lasting armed conflict, political instability, potential design flaws and poor maintenance of dams all contributed to the disaster. The interaction of these factors, and the very heavy rain that was worsened by climate change, created the extreme destruction.

 

The study was conducted by 13 researchers as part of the World Weather Attribution group, including scientists from universities and research centres in Greece, the Netherlands, the United Kingdom and the United States.

 

According to Julie Arrighi, Director at the Red Cross Red Crescent Climate Centre, “This devastating disaster shows how climate change-fueled extreme weather events are combining with human factors to create even bigger impacts, as more people, assets and infrastructure are exposed and vulnerable to flood risks. However, there are practical solutions that can help us prevent these disasters from becoming routine such as strengthened emergency management, improved impact-based forecasts and warning systems, and infrastructure that is designed for the future climate.”