Atmospheric Rivers: What Are They and How Do They Affect Us?

When someone thinks of the atmosphere, they probably think of gases such as nitrogen and oxygen. Most people do not realize that the atmosphere can also hold an entire river of water.

What Is an Atmospheric River?

Atmospheric river refers to the long, flowing regions of the atmosphere which carry water vapor through the sky. They are about 250 miles (402 kilometers) to 375 miles (604 kilometers) wide and can be over 1,000 miles (1,609 kilometers) long.

As a concentrated band of moisture and wind that transports large amounts of water vapor, atmospheric rivers are considered the largest and most important transport mechanisms of freshwater on Earth.

While rivers on land generally flow downhill, atmospheric rivers flow in the direction of moving air created by weather systems. Just like terrestrial rivers, atmospheric rivers can vary in size and strength and occur in both hemispheres. In the North Hemisphere, the atmospheric river typically occurs between December and February, while it takes place from June to August in the Southern Hemisphere when extratropical cyclones are prevalent.

This plume of moisture usually begins over tropical regions. Warm temperatures in these areas cause ocean water to evaporate and rise into the atmosphere. Strong winds help carry the water vapor through the blanket of air, and as the atmospheric rivers move over land, the water vapor rises farther into the atmosphere. As it cools into water droplets, it falls as precipitation over land in cooler regions in rain or snow.

One of the most well-known atmospheric rivers is "Pineapple Express" which picks up warm, moist air near Hawaii. When it hits land in the Western United States and Canada, it causes heavy rain and snow. In California, this atmospheric river can cause up to 5 inches (13 centimeters) of rain daily.

What are the Effects of Atmospheric Rivers?

Atmospheric rivers are important in transporting precipitation in the Northern and Southern Hemispheres. They affect ecosystems and global freshwater supply by providing water security for communities and keeping the water cycle balanced.

Atmospheric rivers have both advantages and disadvantages. The fast-changing climate causes shifts in these long, flowing regions of the atmosphere, resulting in an increased number of extreme weather events that can greatly affect the planet.

Some of the benefits of this phenomenon include the increased water levels and snowpack in watersheds. Since only 1.2% of all freshwater is readily available surface water, freshwater supply must be redistributed. When there are increased water levels in watersheds, it can replenish groundwater reserves, promote ecosystem biodiversity, and maintain the overall health of a watershed.

Freshwater is stored as snowpacks during the cold months and melts into liquid during warmer months. This replenishes the watershed and brings water back to normal levels. Moreover, the ability of the snowpack to reflect sunlight into the atmosphere helps cool the Earth's surface.

Meanwhile, atmospheric rivers can bring disadvantages, such as major flooding, mudslides, and landslides. Atmospheric rivers can carry large volumes of rain, which could make landfall and lead to soil saturation. As a result, the soil can no longer absorb water, causing it to accumulate and lead to flooding.