THE atmospheric rivers they are moving to higher latitudes, and this is changing weather patterns around the world. This is shown by a study led byUniversity of California at Santa Barbara (USA), which indicates how this shift is causing waves of drought but also of floodsputting the water resources of entire communities at risk.
What are atmospheric rivers and where are they found
As he explains National Oceanic and Atmospheric Administration (NOAA)atmospheric rivers are relatively long and narrow regions in the atmosphere, “similar” to rivers in the skywhich carry most of the water vapor out of the tropics.
In general these can vary greatly in size and strength, but the average atmospheric river carries an amount of water vapor approximately equivalent to the average flow of water at the mouth of the Mississippi River. Exceptionally strong ones can carry though up to 15 times that amount.
When atmospheric rivers hit the ground, they often release this water vapor as rain or snow, and those containing the largest amounts of water vapor and the strongest winds can generate extreme rainfall and floodinginduce landslides and cause catastrophic damage. A well-known example is the ‘Pineapple Express‘, a strong atmospheric river capable of bringing moisture from the tropics near the Hawaii up to the west coast of the United States.
California depends on atmospheric rivers up to 50% of its annual precipitation, and a series of winter ones can bring enough rain and snow to end a drought.
But they are not just a question”made in USA”, they form in many parts of the world, including the southeastern and western coasts of the United States, southeast Asia, New Zealand, northern Spain, Portugal, the United Kingdom, and south-central Chile.
Why shifting atmospheric rivers is changing the global climate (but also local climates)
According to what is reported in this new work, atmospheric rivers have move about 6-10 degrees towards the two poles over the last four decades, and it is already a huge problem.
The shift is worsening drought in some regionsintensifying floods in other and putting water resources are at risk that many communities rely on – writes Zhe Li, first author of the study in The Conversation – When atmospheric rivers reach the far north of the Arctic, they can also melt sea iceinfluencing the global climate
What is of particular interest to climate scientists is the collective behavior of atmospheric riverscommonly observed in the extratropics, between latitudes of 30 and 50 degrees in both hemispheres, which include most of the continental United States, southern Australia and Chile
A shift in atmospheric rivers can have great effects also on local climates. In the subtropics, where atmospheric rivers are becoming less common, the result may be longer droughts and less water.
At higher latitudes, atmospheric rivers moving poleward could cause more extreme rainfall, floods and landslides in places like the US Pacific Northwest, Europe, and even the polar regions.
In the Arctic, more atmospheric rivers could accelerate the melting of sea ice, contributing to global warming and affecting the lives of animals that depend on ice.
What is this shift due to?
One of the main reasons for this shift are i changes in sea surface temperatures in the eastern tropical Pacific – the scientists explain – Since 2000, waters in the eastern tropical Pacific have had a cooling trend, which affects atmospheric circulation around the world. This cooling, often associated with La Niña conditions, pushes atmospheric rivers poleward
Sea surface temperatures change over the months along the equator in the eastern Pacific Ocean. Those that are hotter than normal indicate the formation of El Niñothose colder than normal La Nina.
But a study conducted in Australia in 2023 also indicates that global warming caused by human activities is contributing to intensify atmospheric and oceanic phenomena such as El Niño and La La Niña.
Not only that: global warming itself will increase the frequency and overall intensity of atmospheric rivers, because a warmer atmosphere can hold more moisture.
As the world warms, atmospheric rivers, and the critical rainfall they bring, will continue to change course. We must understand and adapt to these changes so that communities can continue to thrive in a changing climate
How this might change as the planet continues to warm is currently less clear, however. The study indicates that at this point it is necessary to review climate models.
Movements lift important questions about how climate models predict future changes in atmospheric rivers – concludes the scientist – Current models may underestimate natural variability, such as changes in the tropical Pacific, which can significantly influence atmospheric rivers. Understanding this connection can help meteorologists do better predictions of future precipitation patterns and water availability
The work was published on Science Advances.
Sources: The Conversation / Science Advances / NOAASatellites/Youtube / NASA/Goddard Space Flight Center Scientific Visualization Studio/Youtube
