The terrible floods in Spain are another devastating blow in an autumn in which climate extremes continue to occur

Even for an era of more extreme weather, this fall appears to have kicked into high gear, particularly in a rain-weary Europe, where massive and deadly floods in Spain's Valencia region are the latest incarnation.

At least 95 people have died in flooding that has left cars piling up like flotsam on beaches, while an ocean away across much of the United States is experiencing a nearly rain-free October that has led to a sudden drought.

Scientists trying to explain what is happening, particularly amid a spate of deadly rainstorms in Europe, see two likely links to human-caused climate change. One is that warmer air stores and then releases more rain. The other is possible changes in the jet stream — the flow of air over land that moves weather systems around the globe — that produce extreme weather.

Several climate scientists and meteorologists said the immediate cause of the flooding was a truncated, lower-pressure storm system that originated from an unusually wavy and stalled jet stream. This system simply parked over the region and poured rain. This happens so often that in Spain they call them DANAs, the Spanish acronym for the system, meteorologists said.

In America, it was a sunny high-pressure system with no moisture that descended like a dome, keeping storms away.

“If we get all the dryness, someone else gets all the rain,” said Jeff Masters, a Yale Climate Connection meteorologist and co-founder of Weather Underground.

“The same extremely wavy jet stream that is causing the drought in the United States is also responsible for the terrible flooding in eastern Spain,” said climate scientist Jennifer Francis of the Woodwell Climate Research Center in Cape Cod. She is a pioneer of a theory that calls for a wavier and The slower-flowing jet stream is attributed to climate change because the Arctic is warming so much that it is no longer much colder than the rest of the planet. This theory is gaining increasing acceptance, but is not fully embraced by the climate science community.

“Attributions are always difficult. “In general, the jet stream has more pronounced waves because of the changes we are seeing due to climate change,” said Maria Jose Sanz, scientific director of the BC3 Basque Center for Climate Change. These DANAs occur when there are more waves, often in winter, she said.

ETH climate researcher Erich Fischer is not yet entirely convinced by the wave-shaped jet stream theory, but then he lists the cut-off low storm systems that have flooded and inundated Europe this autumn: floods last week in France, twice in Italy in September and October in Austria and the Czech Republic in September. And then there are the October floods in the Balkans, but Fischer isn't sure they're quite similar. According to the European climate service Copernicus, parts of Poland, Germany and the Czech Republic received three months' worth of rain in just five days in September.

“I was only talking about them in the fall. “We had a whole series of flash floods in the Alps in the summer,” said Fischer. “Starting with Bavaria, southern Germany in June, then there were about six events in Austria and Switzerland in the mountains, extreme thunderstorms and now this fall. “So it's been an extremely unusual stretch given the heavy rain.”

He said systems, particularly in Spain, France and Austria, remained stuck and “the rain did not move out of the same valleys for hours.”

“It’s unbelievable,” he said.

Even without the possible changes to the jet stream, several scientists are certain that basic physics makes storms like this wetter.

It is a core equation in physics called the Clausius-Clapeyron relationship. It is said that air can hold 7% more moisture for every degree Celsius it warms (4% more for every degree Fahrenheit). The world has warmed by 1.3 degrees Celsius due to greenhouse gases, so it rains at least 9 to 10% more, said climate researcher Friederike Otto from Imperial College. She helps run World Weather Attribution, which looks for human fingerprints in extreme weather conditions and sometimes finds them, sometimes not.

“It's very clear that climate change has played a role,” especially in short outbreaks like in Valencia, Otto said.

The fact that there is more moisture in the air could be “just the beginning,” said meteorologist Masters. As the moisture condenses, it releases heat energy that enters the storm, invigorating it, strengthening its updrafts and allowing it to draw even more moisture from a larger area, which could increase rainfall by up to 20%, he said .

“It just feeds on itself and it becomes a vicious cycle,” he said.

Fischer found a similar storm at the same location in 1957. However, this year's storm was much wetter because it was fueled by warmer air. The 1957 storm dropped about 250 millimeters (10 inches) of rain, but this week there were reports of more than 490 millimeters (19 inches) in just eight hours, Fischer said. There may be problems with the rain gauge, but part of it is that the atmosphere is storing and releasing more water.

And then there is a pleasant Mediterranean sea.

In mid-August, it had the warmest surface temperature on record, with an average temperature of 28.47 degrees Celsius, said Carola Koenig of the Center for Flood Risk and Resilience at Brunel University of London.

“This allows for greater absorption of moisture in the air, leading to more rain as the atmosphere cools in the fall,” she said. “From today’s perspective, Spain must prepare for persistent heavy rain in the next few days.”

You can count and attribute climate change and the devastation it wreaks in different ways, Otto said, but one thing is certain: “Burning fossil fuels causes climate change, and climate change leads to death and destruction.”

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