Spain is being devastated by a weather phenomenon known as DANA, which has caused flash floods resulting in over 155 fatalities.
On October 29, several areas in Spain experienced rainfall equivalent to an entire year’s worth in just a few hours, leading to severe flooding that destroyed numerous towns and left thousands stranded. In some locations, rainfall reached 50.8 cm (500 liters/m2). The cause of this disaster is a phenomenon formed in the Mediterranean called Depresión Aislada en Niveles Altos (DANA), meaning isolated depression at high levels. This is the most severe instance of DANA recorded in the 21st century, according to the Spanish Meteorological Agency (Aemet).
Flash floods inundate towns in Valencia. (Photo: Andalou).
What is DANA?
DANA occurs when a mass of warm air meets cold air stagnating at an altitude of about 9,000 meters. In the stratosphere, there is a strong wind current surrounding the Earth like a belt. Sometimes, this current begins to oscillate, moving in a snake-like manner rather than in a straight line. This oscillation can become “trapped,” allowing cold air to remain in one place.
On October 29, in the southeastern region of Spain, DANA lingered over the same area for more than 12 hours, making that day the most severe weather event recorded and is expected to continue with reduced intensity until November 3. DANA utilizes warm water as fuel, according to meteorologist Mar Gómez. DANA encountered water temperatures of 22 degrees Celsius off the coast of Valencia, while the normal temperature for this time of year is 21 degrees Celsius. The temperature contrast, combined with humidity and energy from the Mediterranean Sea, which remains very warm after the summer months, results in strong storms and torrential rain.
“The winds may not be as intense as in a tropical storm, but in terms of intensity and rainfall, they can actually exceed those of typical tropical storms,” said Jorge Olcina, director of the Meteorology Laboratory at the University of Alicante.
Iago Pérez, a geological scientist at the University of Oxford, described DANA as one of the most dangerous meteorological phenomena in Spain because “they release enormous amounts of water in a very short time.” DANA only forms over Spain, but similar weather patterns called extratropical cyclones can form in the Atlantic Ocean off Uruguay and Argentina.
The Impact of Climate Change
Both Gómez and Olcina noted that the severity of DANA this week is directly related to climate change. However, Pérez believes that linking the phenomenon to global warming requires deeper analysis.
The Mediterranean Sea is one of the fastest-warming basins in recent decades. It acts as “a conveyor of moisture and energy,” according to Olcina. Since the 1980s, the average temperature of the Mediterranean has increased by 1.5 degrees Celsius, nearly double the increase in air temperature in the region over the same period. Since 2020, summers in the Iberian Peninsula have recorded record temperatures, and this year, sea surface temperatures exceeded 29 degrees Celsius.
This warming is altering the timing of DANA events, as the Mediterranean now begins to warm in May and maintains that warmth until the end of November. Between the mid-1980s and 1990s, this phenomenon typically occurred in September and October. Currently, it is estimated that the frequency of DANA occurrences each year has increased by 15-20% compared to six decades ago.
For researchers, this event provides important lessons, including the need for improved early warning systems. Climate change is likely fueling more frequent severe rainfall events. This highlights the urgent need to adjust flood prevention systems and rehabilitate vulnerable areas to mitigate risks associated with increasing extreme weather, according to Olcina.
