The probability that the DANA that has devastated different areas of Valencia would have occurred would have been reduced by half if we were not immersed in the current context of climate change. It is not a conjecture, but an opinion of meteorological experts, since the first scientific studies have begun to appear that directly relate this event of torrential rains to climate change, although more detailed analyzes must be carried out to confirm it precisely. .
The first preliminary study that has linked this catastrophe with the global warming situation comes from the World Weather Attribution (WWA) organization, which indicates that climate change is probably the main factor responsible for this phenomenon. The reason seems to lie in two key factors, which in both cases are associated with an average global temperature increase of +1.3°C compared to the pre-industrial era and whose consequences are:
- “Tropicalized” and warmer air: air temperatures in the Mediterranean are increasing at a rate 20% higher than the global average. Just before the heavy rains in Valencia, a mass of warm subtropical air from Tunisia moved north, coming into contact with the Mediterranean.
- An overheated Mediterranean Sea: in the last two summers, Mediterranean temperatures have reached record levels, with maximums of between 28°C and 30°C. Although they are currently somewhat lower, they are still above usual. In particular, on Saturday, the Valencia buoy registered 21.9°C on the surface. The moisture-laden air favors torrential rains in the interior when it is carried by easterly winds towards the precoastal mountain ranges, where the storm forms.
“The presence of warm air near the surface fed by the excess humidity of the Mediterranean Sea, still hot, and the instability generated by the conflict with the cold air of the upper atmosphere give rise to large convective clouds with heavy downpours and flash floods. ”explained Omar Baddour, head of Climate Monitoring at the World Meteorological Organization (WMO).
The study results are based on observational data, but are in line with existing evidence of climate change signals in similar extreme rainfall events across Europe. They also agree with basic physical principles and the Clausius-Clapeyron relationship, which states that a warmer atmosphere can contain more moisture, resulting in a 7% increase in intense precipitation with a 1°C increase in temperature. Therefore, its authors say they are sure that changes in intense rainfall are driven by human-caused climate change.
How climate change influences the intensity of a DANA
The DANA phenomenon (Isolated Depression at High Levels) already bears the mark of climate change. A study carried out by members of the ClimaMeter project concludes that “DANA-like depressions that cause flooding in southeastern Spain are up to 7 mm/day (an increase of up to 15%) wetter over Spain’s Mediterranean coast today. than they would have been in the past. Furthermore, conditions are up to 3°C warmer in the present compared to the past, which favors the formation of storms over the Mediterranean basin during DANA events.”
The interpretation of these experts is that this DANA has been driven by exceptional meteorological conditions whose characteristics can mostly be attributed to climate change promoted by human activity.
Dominic Royé, head of Data Science at the Foundation for Climate Research (FIClima), who has not participated in any of these studies, told SMC Spain that “this second study is consistent with the one published by the WWA. In my view, there is no doubt that extreme events of this type are more likely now with anthropogenic climate change than otherwise. We know that with every 1ºC increase in global temperature the amount of water vapor in the atmosphere can increase by around 7%. “The more water vapor, the more intense these types of events can be.” And he adds that “drought and extreme rainfall are sides of the same coin. “Warmer temperatures increase evaporation, which reduces surface water and dries out soils and vegetation.”
Conditions are up to 3°C warmer in the present compared to the past, favoring storm formation over the Mediterranean basin during DANA events
In statements to the same medium, the researcher and professor at the Department of Science and Technology of Materials and Fluids of the University of Zaragoza, Pilar Brufau, has pointed out some limitations of the study: “The authors themselves recognize that confidence in the solidity of This approach is low due to the exceptionality of the event in the historical data record. To compensate for this lack of direct comparability, they have had to extend the analysis to analogous events that, although similar, do not share exactly the same characteristics. This limitation in the availability of specific historical data reduces the precision with which the event can be attributed exclusively to anthropogenic climate change. Likewise, the complexity of factors such as the Atlantic Multidecadal Oscillation introduces uncertainty about whether the event responds only to natural climate variability or to the direct influence of global warming.”
On the other hand, Markus Donat, ICREA Professor, co-leader of the Climate Variability and Change group at the Barcelona Supercomputing Center, also agrees that “since the meteorological situation of the recent DANA event was quite specific, there may not be enough meteorological situations similar in the historical record to allow for a robust analysis of how this storm would behave under colder and warmer weather conditions.”
And he concludes: “While it may be difficult to detect changes in the frequency of such weather situations, it is safe to assume that when these weather situations occur in a warmer climate, they can cause heavier downpours. A warmer atmosphere can hold more water vapor, and a warmer Atlantic and Mediterranean can supply more moisture to the atmosphere through evaporation. “More water in the atmosphere means heavier rain associated with storm systems like DANA that affected numerous areas of Spain last week.”
