Climate change made Libya's devastating DANA 50 times more likely and Greece's 10 times more likely

The torrential rains have not given truce in the Mediterranean since the beginning of September with three episodes that have resulted in numerous fatalities and enormous material losses: the devastating DANA in Libya, with 3,958 confirmed victims in the city of Derna and 170 in other areas of the country, although it is feared that the final figure is much higher as there are about 10,000 missing, according to the latest UN estimate; the one that affected Greece (17 deaths), Turkey (at least seven deaths) and Bulgaria (four), and the episode suffered by Spain, with five deaths.

A team of climatologists from the World Weather Attribution (WWA) group published on Monday a quick analysis of whether human-caused climate change is linked to these destructive torrential rains, concluding that the climate made Libya's DANA 50 times more likely and Greece's torrential rains 10 times more likely. Bulgaria and Turkey.

In Spain, where large amounts of water fell in a few hours, they estimate that a DANA like the one we suffered two weeks ago occurs every 40 years. In the case of our country they have not been able to determine if there is a link with climate change since, according to the authors, they have not been able to make a complete analysis as most of the rain has fallen in a few hours. The climate models available for torrential rains, they add, offer unrepresentative data on timescales less than one day so although they believe that climate change has influenced the Spanish DANA, with this study they cannot say for sure.

This type of analysis is called an attribution study and serves to clarify the extent to which human-caused climate change has influenced a particular extreme weather event. Why and for what purpose are these attribution studies done? Because, although one of the main and feared effects of climate change is the increase in the frequency and intensity of extreme weather events (such as heat waves and cold waves, droughts or torrential rains), not all episodes that occur can be directly attributed to climate change. In addition, the degree of influence of climate change also varies in the phenomena in which it has played a role, that is, in some it has a greater influence than in another.

To make that estimate and determine the role of climate change, they analyze existing climate data and use computer models with simulations to compare what the climate is like today (1.2 degrees warmer than at the beginning of the industrial era) and how it was before.

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The conclusion of this team of WWA scientists is that climate change made Libya's DANA 50 times more likely, an episode they define as "extremely unusual" and that in the context of the current climate, it is expected to occur once in 300-600 years.

In the case of Libya, the report highlights that behind this tragedy are also other human factors, as it concludes that the destruction caused by heavy rains was much greater due to construction in flood-prone areas, the poor state of the two dams that collapsed, deforestation and the consequences of the political conflict in Libya. In addition to the lack of maintenance, experts note that the Al-Bilad and Abu Mansour dams were built in the 1970s, using relatively short rainfall records, so they note that they may not have been designed to withstand a rainfall event that occurs once every 300-600 years.

They also point out that although in Libya the weather forecast was known three days in advance, it was not effectively transmitted to the population or to the emergency services so they ask that the warning systems be improved to be able to anticipate and prevent the worst effects.

For Greece, Bulgaria and Turkey, affected by torrential rains for four days, the conclusion is that these were 10 times more likely due to climate change. On the rarity of the phenomenon, they consider that for central Greece, the most affected area of the country, it is estimated that an episode of this type can occur once every 80-100 years, which means that each year there is a 1-1.5% chance of it occurring.

However, for the rest of the large region affected by the rains (Greek, Turkish and Bulgarian territory), scientists believe that it is a "reasonably common" phenomenon since it occurs once every 10 years or so, which means that there is a 10% chance of it occurring each year.

In the case of Spain, the study indicated that such a DANA occurs every 40 years or so. Torrential rains occurred in relatively small areas within a few hours, and most of the climate models they use do not represent rainfall well on these small scales so they have not been able to perform the full attribution study. However, they say that although they cannot completely rule out the possibility that climate change has not influenced the probability and intensity of phenomena such as the Spanish DANA, they do believe that it played a role for several reasons.

Among the reasons are that rising temperatures generally lead to heavier rainfall and several studies predict that as temperatures rise, more torrential rains occur, and that data from weather stations in the affected Spanish regions show a trend towards heavier rainfall.

Infrastructures adapted to the new climate

It is not only in Libya that the vulnerability of the population for the above reasons - a long-standing armed conflict, instability and possible design flaws and poor maintenance of dams - has aggravated the situation. The 13 experts who signed this study, from centers and universities in Greece, the Netherlands, the United Kingdom and the United States, highlight that the large impacts observed in some of the regions were caused by a combination of high vulnerability of the population and its exposure to the phenomenon itself. For example, in the affected area in central Greece, most towns and much of the infrastructure are in flood-prone areas. The interaction of these factors and heavy rainfall worsened by climate change created extreme destruction.

Therefore, experts consider it essential to design and maintain infrastructures not only for the climate of the present or the past, but also taking into account projections for the future: "In Libya, in the long term this means taking into account the decrease in average rainfall and, at the same time, the increase in extreme precipitation such as this event of heavy rainfall."

• Environment