Atmospheric rivers are extraordinary weather phenomena often described as "rivers in the sky." These storms can unleash vast amounts of rain, leading to severe flooding, triggering mudslides, and resulting in significant loss of life and property damage. Understanding how these systems form, their dimensions, and their potential impacts is essential for preparing for their effects.

What Exactly Is an Atmospheric River?

This remarkable weather system can be observed around the globe. The formation of an atmospheric river begins when a substantial amount of water vapor is transported from tropical oceans by high-altitude jet streams toward land. As this moist air ascends, it cools and condenses, leading to the formation of rain or snow.

Atmospheric rivers most frequently develop over mid-latitude oceans, specifically in regions that lie between approximately 30 and 60 degrees north and south of the equator, as outlined by NASA. They manifest as elongated trails of wispy clouds that can extend for hundreds of miles across the sky, making them a striking sight and a significant meteorological phenomenon.

How Do Atmospheric Rivers Cause Flooding?

While many atmospheric rivers are relatively weak and harmless, providing necessary rain or snow for various ecosystems, others can be devastating. The National Oceanic and Atmospheric Administration (NOAA) has indicated that some of these weather systems can transport water equivalent to up to 15 times the flow of the Mississippi River, which can result in catastrophic flooding when they make landfall.

In California, for instance, atmospheric rivers have had a dual impact. They have been responsible for triggering mudslides, toppling utility poles, and blocking critical roadways, yet they have also played a vital role in replenishing reservoirs that had run dry and reducing the risk of wildfires by saturating the region's parched vegetation. An illustrative example occurred in 2019 when an atmospheric river dubbed the "Pineapple Express" struck California. This event, characterized by moisture from near Hawaii, resulted in significant rainfall that caused mudslides, forcing motorists into perilous situations and leading to homes sliding downhill.

Moreover, in 2021, British Columbia experienced a devastating atmospheric river that delivered an entire month's worth of rain within just two days. This extreme weather event resulted in deadly floods and landslides that brought destruction to communities and cut off access to Canadas largest port, illustrating the profound impact of these atmospheric systems.

How Will Climate Change Influence Atmospheric Rivers?

According to scientists, the atmospheric rivers that have caused significant damage in places like California and British Columbia in recent years are projected to become larger and potentially more destructive due to climate change. Research from the American Meteorological Society highlights that columns of air several hundreds of miles long can transport water vapor over oceans from tropical regions to temperate areas, conveying volumes more than double that of the Amazon River.

Although a 2018 study predicts a 10 percent decline in the overall number of atmospheric rivers in the future, it also forecasts that those that do form will be on average 25 percent wider and longer and will carry a greater volume of water. This change poses challenges for water resource management, as moderate atmospheric riverstypically beneficial for water supplieswill become rarer, while the stronger systems may lead to increasingly catastrophic consequences. As these weather phenomena evolve, it will be crucial for communities and policymakers to adapt their strategies for managing water supplies and addressing the potential for flooding and other disasters.

(Compiled by Reuters staff; Editing by Will Dunham)