Explainer. What caused the devastating flash floods in Eastern Spain?

In a matter of minutes, flash floods caused by heavy downpours in eastern Spain swept away everything in their path. People were trapped in vehicles, homes and businesses with no time to react. Many died and thousands saw livelihoods shattered.

Four days later, authorities have recovered 211 bodies — most of them in the eastern Valencia region. They continued to search for an unknown number of missing people on Friday.

• Read: Thousands join effort to clean up catastrophic Spanish floods

Thousands of volunteers were helping to clear away the thick layers of mud and debris that still covered houses, streets and roads, all while facing power and water cuts and shortages of some basic goods. Inside some of the vehicles that the water washed into piles or crashed into buildings, there were still bodies waiting to be identified.

Here are a few things about Spain’s deadliest storm in living memory:

What happened?

The storms concentrated over the Magro and Turia river basins and, in the Poyo riverbed, produced walls of water that overflowed riverbanks, catching people unaware as they went on with their daily lives, with many coming home from work on Tuesday evening.

In the blink of an eye, muddy water covered roads and railways and entered houses and businesses in villages on the southern outskirts of Valencia city. Drivers had to take shelter on car roofs, while residents tried to take refuge on higher ground.

River water churns, with a partially collapsed bridge seen in the background, after torrential rains caused flooding in the town of Carlet, Valencia region, Spain, October 30, 2024. REUTERS/Eva Manez | Photo Credit: Eva Manez

Spain’s national weather service said that in the hard-hit locality of Chiva, it rained more in eight hours than it had in the preceding twenty months, calling the deluge “extraordinary.” When the authorities sent the alert to mobile phones warning of the seriousness of the phenomenon and asking people to stay at home, many were already on the road, working or covered in water in low-lying areas or garages, which became death traps.

Why did these massive flash floods happen?

Scientists trying to explain what happened see two likely connections to human-caused climate change. One is that warmer air holds and then dumps more rain. The other is possible changes in the jet stream — the river of air above land that moves weather systems across the globe — spawn extreme weather.

Climate scientists and meteorologists said the immediate cause of the flooding is a cut-off lower-pressure storm system that migrated from an unusually wavy and stalled jet stream. That system simply parked over the region and poured rain. This happens often enough that in Spain, meteorologists say, they call them DANAs, the Spanish acronym for the system.

Miguel, 69, washes his sweeping brooms in the Dry River (Rio Seco) after cleaning his house, amid flooding caused by heavy rains, in La Hoz de la Vieja, Teruel province, Spain October 30, 2024. | Photo Credit: NACHO DOCE

And then there is the unusually high temperature of the Mediterranean Sea. It had its warmest surface temperature on record in mid-August, at 28.47 degrees Celsius (83.25 degrees Fahrenheit), said Carola Koenig of the Centre for Flood Risk and Resilience at Brunel University of London.

The extreme weather event occurred after Spain battled prolonged droughts in 2022 and 2023. Experts say that drought and flood cycles are increasing with climate change.

Has this happened before?

Spain’s Mediterranean coast is used to autumn storms that can cause flooding, but this episode was the most powerful flash flood event in recent memory.

Older people in Paiporta, ground zero of the tragedy, claim that Tuesday’s floods were three times as bad as those of 1957, which caused at least 81 deaths and were the worst in the history of the tourist eastern region. That episode led to the diversion of the Turia watercourse, which meant that a large part of the city was spared of these floods.

Valencia suffered two other major DANAs in the 1980s, one in 1982, with around 30 deaths, and another one five years later, which broke rainfall records.

This week’s flash floods are also Spain’s deadliest natural tragedy in living memory, surpassing the flood that swept away a campsite along the Gallego River in Biescas, in the northeast, killing 87 people in August 1996.

What has the state response been?

The Valencian government classified the crisis as level two on a scale of three. The crisis is in the hands of the regional authorities, who can ask the central government for help mobilising resources.

At the request of Valencia’s president, Carlos Mazón, of the conservative Popular Party, Socialist Prime Minister Pedro Sánchez announced Saturday the deployment of 5,000 more soldiers who will join rescue efforts, clear debris and provide water and food over the weekend.

The government will also send 5,000 more national police officers to the region, Sánchez said.

At present, some 2,000 soldiers from the Military Emergency Unit, the army’s first intervention force for natural disasters and humanitarian crises, are involved in the emergency work, as well as almost 2,500 Civil Guard gendarmes—who have carried out 4,500 rescues during the floods—and 1,800 national police officers.

When many affected people felt abandoned by the authorities, a wave of volunteers took to the streets to help. Hundreds of people have walked several kilometres daily to deliver supplies and help clean up the worst-affected areas by carrying brooms, shovels, water and basic foods.

Sánchez’s government is expected to approve a disaster declaration on Tuesday that will allow quick access to financial aid. Mazón has announced additional economic assistance.

The Valencia regional government had been criticised for not sending out flood warnings to mobile phones until 8 pm on Tuesday, when the flooding had already started in some places and well after the national weather agency issued a red alert indicating heavy rains.