The flooding in eastern Spain, already the deadliest disaster in the country’s recent history, is a foretaste of the extreme storms that the region can expect to see more of as humans continue heating up the planet, scientists said this week.
Because warmer air holds more moisture, the likelihood of severe downpours rises with every extra ounce of carbon dioxide that people put into the atmosphere by burning coal, oil and gas for energy.
The storms that caused this week’s deluges were of a type that is familiar to the region each fall. But global warming is helping such storms pack a bigger punch, scientists said, in a warning to local officials about the increasing urgency of flood preparedness.
In the town of Chiva, west of the city of Valencia, nearly 20 inches of rain fell in eight hours on Tuesday, Spain’s meteorological agency said. That’s what the area normally receives in a year.
“We know that extreme rainfall is becoming more extreme and more frequent,” said Andreas Prein, a professor of weather and climate modeling at the Swiss university ETH Zurich. “And we know that our infrastructure is aging and outdated. But being proactive about that is extremely difficult.”
In basic terms, eastern Spain was flooded this week because of a cutoff low: an area of low pressure that breaks away from the jet stream, the fast-moving current of wind that meanders west to east across the globe’s temperate regions.
When a cutoff low forms in the Gulf of Cádiz off southern Spain, it produces winds that blow warm, moist air from above the Mediterranean Sea toward the country’s eastern coast. This moisture-laden air hits the mountains and is pushed skyward, condensing into clouds that dump rain onto coastal areas including the province of Valencia.
Normally the jet stream would whisk such weather systems away relatively quickly. But because cutoff lows are detached from those winds, they can linger in place, blasting the same places with rain for days and days.
Cutoff lows have been responsible for many of eastern Spain’s most catastrophic floods. They also bring drenching rains to the inland regions of the American West and the Great Plains.
The warm water of the Mediterranean added to this week’s rainfall totals in Spain, said Rosana Nieto Ferreira, a professor of atmospheric science at East Carolina University in Greenville, N.C.
When water at the sea surface is warm, more of it evaporates, providing more moisture to fuel downpours. The Mediterranean has been abnormally hot in recent months, reaching its highest temperatures on record in August.
This week’s storms in Spain also produced large hail and tornadoes, an indication of how much energy was present in the low-level air that was sent aloft, said Dr. Prein.
“That’s something you don’t see very often,” he said. “For me, this is exactly what I would expect from climate change.”
In a study published in 2021, Dr. Nieto Ferreira predicted, based on computer simulations, that rain in northeastern Spain from cutoff lows could increase significantly if nations warmed the planet to very high levels this century. Scientists in Britain have come to similar conclusions about downpours of all kinds in eastern Spain and southern France.
As humans heat the planet, “we are loading the dice of extreme weather in the worst way possible,” said Ben Clarke, a research associate studying climate change at Imperial College London.
Researchers are examining another potential way in which greenhouse warming might be affecting extreme weather: The Arctic is heating up faster than the rest of the planet, which is narrowing the temperature difference between it and the tropics. This might be weakening the jet stream and causing it to shift, though scientists have not yet come to firm conclusions about what this might mean for storms and heat waves.
Dr. Nieto Ferreira travels often to eastern Spain. Her family has a home there. When heavy rains hit the region’s small mountain towns, it is no surprise that catastrophe ensues, she said.
“The infrastructure to drain that much water quickly doesn’t really exist,” Dr. Nieto Ferreira said. “The water just doesn’t have anywhere to go.”
In a part of the world where global warming is also leading to longer and more intense dry spells, all this extra water might seem like a blessing. But only if the right infrastructure is there to capture it, Dr. Nieto Ferreira said. For now, in eastern Spain, “that water is mostly going straight into the ocean,” she said.
The post How a Year of Rain Fell on Parts of Spain in Eight Hours appeared first on New York Times.
