What is the “atmospheric river” that brought rain to California after France?

United States National Oceanic and Atmospheric Administration (NOAA) Since late December, California has been affected by a succession of atmospheric rivers that have brought down watercourses and caused untold damage.

CLIMATE – sequence “atmospheric rivers” Flowing to California. After three weeks of unprecedented rain that killed at least 19 people, new bad weather is expected this Sunday, January 15, but US President Joe Biden has declared a state of major disaster in the country’s most populous western US state. It was not a natural phenomenon “Atmospheric River” therefore it drains the water channels.

These are “atmospheric rivers” are actually bands of warm air and are loaded with very strong moisture that carries large amounts of water droplets and can cause very heavy rainfall, climatologist Robert Votard details The HuffPost.

“The amount of water falling is astronomical”

Term “Atmospheric River” it does not have a scientific definition, to be precise, the researcher specifies it. This is a colorful way to bring to life a phenomenon that has been known and studied for years. ” Water evaporates from the oceans, then rises along these fronts and flows over the continents and oceans. These movements form a kind of atmospheric water corridor that can extend to the Atlantic or the Pacific Ocean and create the impression of a river.

If the phenomenon is not exceptional, “What’s happening in California is very unusual, in Southern California it sometimes rains, but never for this long”I would like to mention Robert Wotard. The state is actually facing its eighth “Atmospheric River” in less than a month. Result: “These extreme rainfalls have caused floods, landslides and catastrophic damage to the population”American Oceanic and Atmospheric Administration regrets.

“The amount of water falling is astronomical and quite exceptional, Robert Wotar still wonders. The The location of these storms in the southern part of the state is also very surprising for a La Ni winter.nothere is Recall that La Niña is a cooling climate effect characterized by a cold phase and usually favoring depressions, more so in northern California.

Global warming as the obvious culprit

Global warming plays a major role behind this anomaly in rainfall levels, as the climatologist explains very well: “With climate change, these bands contain more moisture and cause increasingly intense rains. »

It’s actually a feedback loop: the higher the temperature, the more water evaporates from the oceans and the air is charged with moisture, and the more these phenomena occur. “atmospheric rivers” it will be intense. For each additional degree, the atmosphere can contain 7% more water vapor, notes Robert Vautard.

As for the frequency of these events, scientists cannot confirm that these rivers in the sky will become more frequent in the coming years. “Studies show that global warming tends to increase the frequency of this phenomenon, as we have seen in the last decade. But we don’t have any certainty yet.” scroll through the columns Let it go Françoise Vimeux, climatologist and director of research at the Research Development Institute.

And the US and Australia are often affected “atmospheric rivers”, Europe will not pass through torrential raindrops in the coming years. Moreover, France experienced a depression similar to this phenomenon in late December and early January, and was the result of very heavy rain on New Year’s Eve.

“Until the end, New Year’s Eve 2022 will be a symbol of extreme and human-induced climate change. Expected temperature records, but also torrential rains due to the atmospheric river (…)”, CNRS research director and climatologist Christophe Cassou reported on his Twitter account on December 31, 2022. The great mildness of the end of the year also strengthened this phenomenon. And in less than three days, the equivalent of nearly a month’s worth of rain fell on Brittany.

Storm Gérard, “atmospheric river”?

The beginning of 2023 was also well watered. On January 10, it fell in just 24 hours, the equivalent of three weeks and a month of rain in the Pyrenees massif.

And again this Sunday: storm Gerard reaches France from the western front and will cross the country on January 15 and January 16. “ This deep depression is driving the storm from the Atlantic coast to the north of the country, with winds of 120 km/h offshore and 90-100 km/h inland. At La Chaîne Météo, meteorologist Gilles Matrico analyzes.

“Today a spectacularly disturbed system in the north, well supplied with water from a (modest) atmospheric river, with a surprising (but no longer surprising) sweetness near the Pyrenees: 20 ° C”added this Saturday 14 Francois Jobard meteorologist at Météo France.

If Francois Jobard calls a “Atmospheric River” Robert Vautard would not use this term to describe Gerard’s storm: “Personally, I would say this is a hurricane, a depression that will deepen very quickly and bring a lot of rain and moisture. »

Unfortunately, this flood in France will not be enough to compensate for the precipitation deficit from early 2022. “It’s good news for the tables, but it’s going to take a few episodes like this to fill them up”he adds that the summer drought of 2023 already looks worse than 2022.

See also The HuffPost:

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