Atmospheric river: the current of moisture that causes natural disasters
A recent post by Scripps Institution of Oceanography) on the Pacific Northwest and California.”
In an article published in The Conversation, hydrologist Qian Cao, who, like the research institution, also works at the University of California, San Diego in the USA, explains the concept of “atmospheric rivers” and how these sometimes overwhelming storms are also essential for the water supply in the affected regions.
Fundamental elements in the transport of water in the atmosphere, atmospheric rivers play a critical role in distributing water around the planet. However, in certain situations, the concentration of moisture in one of these “rivers” can result in intense rain, with precipitation capable of causing floods and impacting some regions.
What is an atmospheric river?
CW3E AR Update: The first of two strong ARs made landfall over BC and the PNW today, continuing a period of active weather over the USWC. The second strong AR is forecast to make landfall Tue and move down the coast, the speed at which it progresses likely impacting how much… pic.twitter.com/jW5gbEmZGn
— CW3E Scripps (@CW3E_Scripps) January 29, 2024
The call Atmospheric river is nothing more than a narrow band or filament of concentrated water vapor that moves through the atmosphere. Flowing through the sky in the same way as a terrestrial river, these air currents can reach 1,600 kilometers in length, with a flow rate that can reach twice the regular flow of the Amazon River.
Regularly transporting vaporized water from oceanic regions to land areas, these rivers are present throughout the world and, when they run against mountains or enter atmospheric dynamics, they are compelled to rise. When this occurs, the moisture they carry cools and condenses, resulting in torrential rain or heavy snowfall.
According to Cao, although they occur throughout the planet, atmospheric rivers are more concentrated in mid-latitudes, areas between the tropics and the polar regions. This causes these countries, such as the USA, Canada, parts of Europe, China and Japan, to experience more delineated seasonal variations than those close to the equator, such as Brazil.
Why are atmospheric rivers dangerous and also necessary?
In hydrological dynamics, the “families” known as consecutive atmospheric rivers are the most dangerous, as they can cause severe flooding. Furthermore, as precipitation persists in soils that cannot absorb more water, river floods occur and impacts on urban infrastructure. Hence the need for constant monitoring and forecasting of atmospheric rivers to alert populations and reduce risks.
However, as a research hydrologist, Cao prefers to focus on the importance of atmospheric rivers in water supply in the West. For him, these atmospheric currents were responsible for ending more than a third of the region's major droughts, as they “provide an average of 30% to 50% of the West Coast's annual precipitation.” They are also responsible for 30% to 40% of all accumulated snow, says the hydrologist.
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