A new attribution study finds the probability of such storms has increased compared with the period prior to the climate crisis
Yarden Michaeli. Sep 20, 2023
A study published on Tuesday determined that the climate crisis exacerbated storm Daniel which this month caused serious flooding in a series of countries in the Mediterranean Basin, covered over 700 square kilometers (270 square miles) in Greece in water and destroyed dams in Libya, creating floods that killed thousands of people.
According to the international research team, the probability of such a storm happening has increased compared with the period prior to the climate crisis (which is caused mainly by the burning of gas, oil and coal). The researchers also noted that the combination of heavy rains and neglect by authorities, faulty planning as well as additional human factors rendered the storm particularly destructive and lethal.
A team comprising 13 researchers from all over the world focused on the storm that, over 10 days, brought extreme rainfall to several countries including Spain, Greece, Bulgaria, Turkey and Libya. In the city of Derna in Libya, the flood that resulted from the storm and the collapse of neglected dams erased entire neighborhoods and caused the uprooting of 30,000 people. It will take the country many years to recover from this humanitarian disaster. In Greece, the storm flooded broad expanses in the center of the country and dealt a grave blow to agriculture.
“This event was a breaking point in Greece,” says Kosta Lagouvardos at the National Observatory of Athens. “From now on we will speak about what happened before and after Daniel,” he said at a press conference where the study was presented. “We have to re-examine all the procedures and our preparation for such events.”
Because the storm moved around the Mediterranean and caused differing damage to each country, the research team examined the countries separately. In Libya, the researchers found that climate change may have made the extreme rain as much as 50 times more likely and 50 percent more intense. They also found that human-induced climate change may have increased the intensity of the rainfall seen in Greece, Bulgaria and Turkey by as much as 40 percent. Additionally, it could make such intense rain 10 times more likely.
According to the study, the extensive destruction in Greece was caused by “a combination of high vulnerability of the population and their exposure to the event,” which was worst in flood-prone central Greece. In Libya, numerous factors including “long-lasting armed conflict, political instability, potential design flaws and poor maintenance of dams” as well as the storm itself which was exacerbated by climate change, contributed to the decimation. Open gallery view
Such a storm is now expected to take place once in a decade in the region encompassing all three countries. In today’s climate, before the additional warming that’s guaranteed to plague the planet, this is still a rare event that should take place only once every 300 to 600 years.
The scientists of the World Weather Attribution collective, who authored the study, specialize in a swift analysis of extreme weather events and generally publish their findings in proximity to the events they describe. The study has yet to be published in a scientific journal, but the members of the team use methods that have undergone peer review and are accepted by the scientific community.
A comparison between two worlds
The global climate is a complex system that is affected by many variables. Examining whether a specific extreme weather event is related to the climate crisis requires considerable effort, large quantities of data and powerful computers. Attribution studies, in which researchers examine the degree of influence of human activity on extreme weather events, are studies of the sort that can provide the answers.
The basic idea is to use climate data and simulations of computerized models to compare the likelihood that a specific extreme event will take place in the present global climate to the likelihood that it would take place in the global climate that existed before the start of global warming, in the late 19th century. The difference between the two scenarios enables scientists to determine the contribution of human beings to the occurrence of a specific extreme weather event. In this way scientists have already discovered the connection between human activity and hundreds of extreme weather events.
The researchers who conducted the present study noted that there is a certain degree of uncertainty regarding the findings, since the rain fell in relatively small areas in which, for the most part, climate models find it difficult to analyze weather events. The director of the Israel Meteorological Service, Nir Stav, examined the study and also noted the difficulty of analyzing storms using the existing climate models, and added that choosing the definition of the event and the manner in which it is examined affect the findings.
But Dr. Friederike Otto at Imperial College London, the main author of the study, told journalists that in spite of all the challenges in the present study, “No matter how we looked at the event, which data set we use, or which exact region we use, we find an increase in the intensity and likelihood of the event in the observations. And while there are limitations on the data in terms of what the exact return time of the event is, and what the exact magnitude is – that doesn’t affect the climate change signal very much,” she says.
The researchers wrote that they are “confident” that the climate crisis played a role in the events of recent days and noted that other studies anticipate heavier rains in this part of the world, and that higher temperatures lead to heavier rains. Indeed, the summer of 2023 broke a long series of heat records and was described as the hottest in recorded history.
And what about Israel?
According to the head of the Meteorological Service, whether a storm of the intensity that hit the Mediterranean Basin this month could reach Israel is still open. In order to answer it with confidence there is a need for high climate computing capacity, which Israel still lacks. The government has yet to establish a computing center that can produce precise forecasts, and even after it is built it will take time until results become available.
However, the head of the Meteorological Service said that already now global warming is causing extremes in the intensity of the rains, as we can learn from a variety of scientific studies and from actual measurements in Israel.
“Proper preparatory steps must be based on the possibility of extremes in the intensity of rain,” Stav says. “The coastal plain region at the start of the rainy season is especially trouble-prone. This phenomenon is combined with intensive urbanization trends on the coastal plain, in which land is replaced by concrete and asphalt and the penetration of water is blocked. As a result we can probably expect a continual increase in urban flooding on the Coastal Plain.”
Stav added that increased flooding is not related to the annual rainfall, but rather to the accumulation of rain falling in shorter windows of time. “These are rains that challenge the drainage systems and the dams,” he says. “According to all our indications, the intensity of the rain is steadily increasing though the annual rainfall isn’t increasing. We are identifying a decline in the number of days of rain, but the amount of rain that falls in 24 hours and the amount of rain that falls in an hour, and even in shorter periods of time, is steadily rising.”