Climate change supercharged Iberian Peninsula’s destructive storms

BRUSSELS — Global warming intensified a series of torrential rainstorms that battered Spain and Portugal in recent weeks, new research has found. 

Nine destructive winter storms hit the Iberian Peninsula with extensive flooding between mid-January and mid-February, killing six people in Portugal, forcing the evacuation of more than 12,000 people in Spain and leaving a trail of devastation across both countries. 

The economic damage was significant: The Spanish government has already allocated €7 billion in relief payments to help people affected, while in Portugal the damage is estimated to reach €6 billion, equivalent to more than 1.5 percent of the country’s GDP. The Portuguese government has said the reconstruction cost will constrain the nation’s finances. 

On Thursday, a team of international scientists published research showing that climate change intensified the rainfall in the Iberian Peninsula as well as neighboring Morocco, where the same storms displaced hundreds of thousands. 

The World Weather Attribution consortium — a group of scientists who run rapid analyses assessing the role of climate change in extreme weather events based on peer-reviewed methods — looked at two specific rainfall events over the last month, one stretching from northwestern Spain into Portugal and another in southern Iberia and northern Morocco.

They found an increase in the intensity of rainfall of 36 percent in the northern region and 28 percent in the southern area. “This means the wettest days are now around a third wetter” than before humans began heating the planet by burning fossil fuels, they write. 

To understand to what degree climate change is responsible for this increase, they ran simulations comparing similar downpours in the present climate and in a world without global warming. The results complicated the picture but nevertheless demonstrated that global warming has driven up rainfall intensity. 

In the northern region, the climate models consistently showed that rainfall was getting heavier, said Clair Barnes, a researcher with the Centre for Environmental Policy at Imperial College London and a co-author of the study. 

“Overall, we estimate that the wettest days are now about 11 percent wetter than they would have been without human-caused climate change,” she said. 

In the southern region, “the climate models actually don’t show any increasing trend in rainfall on the wettest days.” For that reason, “we can’t quantify the effect of climate change on extreme rainfall in that southern area,” Barnes added, but stressed: “This does not mean that climate change didn’t contribute to the extreme rainfall in the southern region as well, just that it’s difficult to detect overall trends over time.” 

Hotter oceans, heavier rain

In particular, the researchers also found that the succession of storms was driven in part by a so-called atmospheric river, a long band of wind and water vapor that transports moisture across vast distances. 

The atmospheric river was “intensified by passing over a very strong marine heatwave in the Atlantic on its way up to Spain,” said Barnes. This increase in sea temperatures, she added, was found to have been made 10 times more likely to happen as a result of climate change. 

“The storm … is carrying moisture from the Atlantic up towards Iberia, up towards northern Morocco, and because this atmospheric river passed over this very warm patch of ocean, it was able to pick up more moisture than it would have if the ocean had been cooler, and that means that when that rain makes landfall … there is more water to fall,” she said. 

A so-called blocked weather pattern — describing a high-pressure area that diverts winds around it — also influenced the extreme weather by channeling storm after storm toward Iberia for a month. Scientists are still investigating whether climate change is increasing the occurrence of blocking patterns.

The authors noted that at an estimated 49 fatalities across the three countries, the death toll remained relatively low, thanks to concerted early-warning and evacuation efforts. 

The precise reconstruction cost of homes, infrastructure and agriculture is still being assessed. The knock-on damages for the economy will likely run even higher; Portugal’s main highway, for example, collapsed in one of the storms in mid-February and is expected to take weeks to repair. 

“These early warning and anticipatory actions reduced loss of life, but they don’t reduce the underlying exposure” to risk, said Maja Vahlberg from the Red Cross-Red Crescent Climate Centre, one of the study co-authors. 

She added: “While humans can be moved out of harm’s way, that’s not true for our homes, our workplaces, our roads, our buildings — carriers of history, culture, and memory.”