What is DANA, the strange weather phenomenon that has caused deadly flooding in Spain?

A strange weather phenomenon known as DANA has caused catastrophic flooding in Valencia, Spain this week. More than 155 people died and dozens remain missing in what meteorologists are calling one of the worst natural disasters in recent history.

On Tuesday (October 29), some areas received the equivalent of a year’s worth of rain in just a few hours, leading to massive flooding that destroyed entire towns and left thousands of people stranded. In some areas it is rainfall reached up to 20 inches of precipitation (500 liters per square meter).).

The cause of this disastrous weather is a phenomenon forming in the Mediterranean called a Depresión Aislada en Niveles Altos (DANA), a Spanish expression that translates to isolated high-level depression. It was the most severe DANA recorded in the 21st century, comparable to catastrophic “Pantánada de Tous” from 1982This was reported by the Spanish Meteorological Agency (Aemet).

What is a DANA?

DANAs are intensified versions of what is known as a “cold drop,” which occurs when a mass of warm air collides with a stationary mass of cold air at an altitude of about 29,500 feet (9,000 meters).

In the upper atmosphere there is a very strong wind current that surrounds the Earth like a belt. Sometimes this current begins to oscillate, looking more like a hose than a belt. When this happens, the oscillation can ‘get stuck’, allowing the mass of cold air to remain in one place. On this occasion it happened over southeastern Spain.

A DANA forms when this cold air and very warm air meet near the surface, especially over the warm waters of the Mediterranean Sea. This combination creates a significant temperature difference between the different layers of the atmosphere, causing the warm air to rise easily and become saturated with water vapor.

When this temperature contrast is combined with humidity and energy from the Mediterranean Sea, which is very warm after the summer months, the result is heavy storms and torrential rains.

“The winds may not be as fierce as a hurricane, but in terms of rainfall and intensity they may even exceed them. These events can cause property damage and loss of life equal to that of an average hurricane. hurricane,” Jorge Olcinadirector of the Climatological Laboratory at the University of Alicante told LiveScience.

A boy cleans up rubble in a flooded street full of crashed cars

The storm dumped a year’s worth of rain in a matter of hours, causing severe property damage and killing more than 155 people. (Image credit: Anadolu via Getty Images)

Iago Pérez, a geoscientist at the University of Oxford, described DANAs as one of the most dangerous meteorological phenomena in Spain, noting that “they release enormous amounts of water in a very short time.”

DANAs only form over Spain, but similar weather patterns, called extratropical cyclones, form in the Atlantic Ocean off Uruguay and Argentina, the researchers said.

On October 29, DANA hovered over the same area for over twelve hours, making it the most intense of the day. weather event – which is expected to continue with less intensity until Sunday (November 3).

DANAs use warm water as ‘fuel’, meteorologist Mar Gomez told LiveScience.

The DANA encountered water temperatures of around 22 degrees Celsius off the coast of Valencia, while the usual temperature for this time of year is around 21 degrees Celsius. That difference seems small, but it is sufficient to provide the storm system with extra energy. This could “cause a cascade of rainfall in a very short period of time,” Olcina said. “This rainfall can be characterized as monsoon-like.”

What does climate change have to do with it?

Gómez and Olcina agree that the severity of this week’s DANA is directly related to climate change. However, Pérez thinks that linking the phenomenon to global warming requires a deeper analysis.

The Mediterranean Sea is one of the marine basins that have warmed the most in recent decades. It acts as a “transmission belt for humidity and energy,” Olcina said. Since the 1980s, the average temperature of the Mediterranean Sea has risen by 1.5 degrees Celsius – almost double the rise in air temperatures in the region over the same period. “Since 2020, summers on the Iberian Peninsula have seen record temperatures, and this year the sea surface temperature has exceeded 29 degrees Celsius,” Olcina said.

This warming has changed the timing of DANAs the Mediterranean Sea is now starting to warm up in May and retains that warmth through November. By comparison, in the 1980s and 1990s this phenomenon typically occurred in September and October. Currently, an estimated 15% to 20% more DANAs are formed each year compared to sixty years ago.

For researchers, this episode offers important lessons, starting with the need to improve early warning communication protocols.

“If there are fatalities, it means something has gone wrong. Communication and anticipation of these events must be improved,” Gómez said.

Climate change is likely to lead to more frequent, intense and exceptional precipitation events. This underlines the urgent need to adapt prevention and protection systems and restructure vulnerable areas to reduce the risks associated with an increasingly extreme climate, Olcina said.