The largest moisture source: where on Earth do the most "rivers in the sky" flow?

Atmospheric rivers are responsible for transporting a significant portion of water vapor on Earth and play a crucial role in the water cycle. Interestingly, they existed long before the dinosaurs appeared, but the term "atmospheric rivers" was first coined and used relatively recently—in 1994, as reported by IFLScience.

Researchers note that atmospheric rivers are considered to be long, narrow columns of water vapor flowing through Earth's atmosphere, somewhat resembling rivers in the sky—hence the name "atmospheric rivers." According to data from experts at the Department of Energy, atmospheric rivers carry water from the tropics near the equator to temperate regions and beyond. They are also a temporary phenomenon, but on average, there are between 4 to 5 atmospheric rivers existing at any given time on the planet.

Researchers believe that one of the most well-known atmospheric rivers in the world is likely the Pineapple Express—it originates in the Pacific Ocean near Hawaii and reaches the west coast of the United States.

NASA researchers indicate that atmospheric rivers typically occur in the extratropical regions of the North and South Pacific and the North and South Atlantic. It is known that atmospheric rivers can extend over vast distances, usually reaching temperate regions approximately between 30° and 60° north and south latitude, such as areas on the west coast of America, Europe, Southeast Asia, and New Zealand. In fact, it is here that they release water in the form of precipitation—rain or snow.

Researchers acknowledge that atmospheric rivers are an integral part of the global system and provide a vital water supply. According to the National Oceanic and Atmospheric Administration (NOAA), up to 30–50% of annual precipitation on the west coast of the United States results from several atmospheric river events. At the same time, in France, Spain, the United Kingdom, and Southeast Asia, atmospheric rivers account for more than 50% of all precipitation.

However, "rivers in the sky" can also cause extreme downpours and flooding, which can lead to landslides and damage to property. For instance, something similar was observed earlier this year in North America; in September, one particularly strong atmospheric river caused several days of heavy rainfall in areas of Canada and southeast Alaska.

Historically, temperate regions received more precipitation from atmospheric rivers; however, scientists have recently discovered changes caused by climate change. Unfortunately, researchers fear that these changes could significantly impact global water supplies. A study published by a group from Santa Barbara found a shift in the position of atmospheric rivers: they have moved an average of 6°–10° closer to the poles over the last 40 years.

Such a shift is thought to potentially lead to stronger droughts in subtropical regions, such as Brazil, as well as wetter conditions in countries closer to the poles, such as those in Europe and states in the northwest Pacific.

Moreover, scientists believe that these changes may exacerbate existing trends, such as the loss of sea ice in the Arctic. As atmospheric river outpourings become more common in polar regions during winter, these areas have less time to recover after summer melting.