Atmospheric rivers are shifting, with global climate impacts

Atmospheric rivers form worldwide as narrow bands of moisture that bring heavy rain and storms. Notably, these rivers are moving toward higher latitudes, which is changing weather patterns globally.

Over the past four decades, atmospheric rivers have moved about 6 to 10 degrees towards both poles. When these systems reach the Arctic, the melted sea ice impacts the climate across the entire globe.

How atmospheric rivers impact our world

From the fertile lands of California and Southeast Asia to the coasts of Spain and Portugal, atmospheric rivers supply over half of the yearly runoff. In California, they can deliver up to 50% of the annual rainfall.

A series of winter storms from these rivers can bring enough rain and snow to end a drought, as seen in parts of the region in 2023. These rivers draw moisture from the tropics, curving toward the poles due to shifts in the jet stream.

Behavior of atmospheric rivers

As with all natural phenomena, no two atmospheric rivers are identical. However, their collective behavior greatly interests climate scientists who study these patterns closely.

These systems are often observed in the extratropics, a region that sits between 30 and 50 degrees latitude in both the northern and southern hemispheres.

Over the past four decades, river activity has shifted away from 30 degrees, with more intense activity now seen along 50 degrees latitude.

Notably, this shift means more atmospheric rivers bringing heavy rain to places like British Columbia and Alaska, increasing the risk of flooding and changing local weather patterns.

Shifting atmospheric rivers

So, why are atmospheric rivers moving poleward? The primary reason is the cooling tendency of sea surface temperatures in the eastern tropical Pacific since 2000.

Associated with La Niña conditions, this cooling effect influences atmospheric circulation worldwide, pushing the rivers towards the poles.

As atmospheric rivers drift poleward, they impact local climates significantly. In the subtropics, where these rivers are becoming less common, more prolonged droughts and water scarcity might become the norm.

Simultaneously, higher latitudes might experience more extreme rainfall and flooding. If atmospheric rivers frequent the Arctic more often, we might witness a rapid melting of sea ice, exacerbating global warming and affecting arctic fauna.

Preparing for what’s to come

While the shifts so far largely reflect natural phenomena, human-induced global warming also plays a role.

As the world gets warmer, the atmosphere can hold more moisture, which makes atmospheric rivers happen more often and with greater intensity.

Predicting these future changes is challenging, mostly because it’s hard to predict the swings between El Niño and La Niña, which greatly influence where these atmospherric rivers go.

At the University of California, Santa Barbara, scientists like Qinghua Ding have been closely studying the poleward shift of atmospheric rivers. By understanding these changes, they hope to improve climate models and better predict future rainfall and water supplies.

Implications for wildlife

The poleward shift of atmospheric rivers doesn’t just impact people – it also affects ecosystems and wildlife.

As more rain moves into northern regions, plants and animals that aren’t used to such heavy rain might face big challenges.

For example, in Arctic areas, changes in rain can alter plant growth, which may disrupt the local balance of nature. This shift could also threaten animals like migratory birds, which need stable habitats for nesting and feeding.

Unpredictable ecosystem changes

In areas where atmospheric rivers are becoming less frequent, ecosystems that rely on steady rain might experience longer dry spells.

Forests in warmer regions, for example, could face more drought, increasing the chances of wildfires and harming biodiversity. Aquatic habitats could suffer too, as less reliable water sources make it harder for fish and other creatures to thrive.

To help protect nature, conservation efforts must adjust to these changes. Protecting vulnerable plants and animals in areas experiencing shifts is essential to maintaining biodiversity.

Ongoing research will play a key role in understanding these impacts and guiding strategies to help ecosystems cope with a changing climate.

The study is published in the journal Science Advances.

Image Credit: NASA Earth Observatory

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