atmospheric rivers, what is this banal phenomenon that increases tenfold with global warming?
A classic phenomenon in winter…
Specifically, the atmospheric river appears as a continuous flow, namely, the Southwest wind, which carries moisture (rain) and heat. When it comes to the Atlantic Ocean, you have to imagine a kind of filament of moisture stretching from the Antilles to continental Europe. Christophe Cassou, director of research at CNRS and lead author of the sixth report, said, “It is, simply put, a series of troughs (two, three, four, etc.) that follow each other in single file (Intergovernmental Panel on Climate Change).
The atmospheric river of the Atlantic Ocean is called the Rum Express. The same phenomenon occurs in the Pacific Ocean, the Pineapple Express (Editor’s note, pineapple) because the source of heat and humidity of this river comes from Hawaii.
Their presence in the Atlantic or Pacific is episodic, averaging two to three per year. But these are classic configurations in winter, which return every year and usually last between three and four days. Therefore, these rivers create significant rainfall events in Europe. Because the precipitation continues, even if it is not necessarily strong.
“Precipitation rates associated with cyclones, atmospheric rivers, and severe thunderstorms increase with every tenth of global warming”
…with global warming, the effects have increased tenfold
In itself, this is a phenomenon that is nothing new. The problem is that global warming amplifies the effects. Whoever says warmer weather is obviously saying that it’s higher temperatures, but also more water vapor, that’s melting Antarctica in particular. “An atmosphere that is one degree warmer can have 7% more water vapor,” says Christophe Cassou. This much additional water is likely to fall in the form of precipitation, it could be a shower.
The good news after a year of historic drought? Not really. “The amount of rain is important, but the way it falls is even more important,” explains the researcher. When rain falls more than once, it penetrates the ground better and therefore recharges water tables more efficiently. But if the same amount falls all at once, it essentially creates runoff (and flooding) and less water is available later. »
However, “the proportion of precipitation associated with cyclones, atmospheric rivers and severe storms increases with every tenth of global warming”, warns Christophe Cassou. With the goal of keeping global warming below 1.5°C no longer clearly achievable, surely this end of 2022 and beginning of 2023 is a glimpse of what lies ahead for the world next. will come.
The worst in 2023 (and 2024)?
We already know that 2023 will be dry in terms of water resources, not necessarily rainy. “Groundwater recharge is very low and natural snow storage is reduced to percolation,” notes Christophe Cassou. Where ski resorts are closing with a vengeance.
“We are in a difficult situation and we are still there”
In terms of temperature, on a planetary scale, 2023 is worse, as El Nino, that warm anomaly in the surface waters of the eastern Pacific Ocean that can affect global climate, is likely to return in the spring. However, for the past three years we have been in more of a La Nina configuration, an inverted cold anomaly. If the return of El Nino is confirmed, “2023 will be hotter than 2022,” the researcher warns. “If not 2023, then 2024.”
