What are atmospheric rivers? Unpacking their global significance

Atmospheric rivers are vast plumes of moisture that travel across the sky, capable of dumping heavy rain or snow when they reach land. These weather phenomena play a critical role in global precipitation patterns and can have both beneficial and destructive impacts.

Where do atmospheric rivers originate?

Atmospheric rivers typically form in tropical regions, where warm temperatures cause water vapour to rise into the atmosphere, according to the National Oceanic and Atmospheric Administration (NOAA). High-altitude winds then transport this moisture to northern and southern latitudes.

While they occur worldwide, atmospheric rivers are especially significant along the West Coast of the United States, contributing 30 to 50 per cent of the region’s annual precipitation. They are vital for water supplies but can also trigger powerful storms, leading to flooding, mudslides, and other hazards.

Formed by winds associated with cyclones, atmospheric rivers generally span 250 to 375 miles (400 to 600 kilometres) in width and move under the influence of broader weather systems. While many atmospheric river events are relatively weak, the strongest can carry seven to 15 times the daily water discharge of the Mississippi River, according to the US Geological Survey. Studies indicate that atmospheric rivers are becoming bigger, wetter and more frequent as the Earth’s atmosphere warms.

What happens when atmospheric rivers reach land?

When moisture-laden air encounters mountain ranges, such as the Sierra Nevada along the California-Nevada border, the rising vapour cools and releases heavy precipitation as rain or snow, NOAA explains.

Unlike traditional cold winter storms that build the Sierra snowpack, atmospheric rivers are often warm. While snow may fall at higher elevations, rain at lower altitudes can accelerate snowmelt, increase runoff and trigger flooding, while also reducing the snowpack needed for California’s water supply.

What is a pineapple wxpress?

A pineapple express is a particularly strong atmospheric river originating near Hawaii in the tropical Pacific, capable of delivering intense rainfall to the US West Coast.

Origins of the term “atmospheric river”

The term “atmospheric river” was first coined in the 1990s by MIT scientists Yong Zhu and Reginald E. Newell. In meteorology, atmospheric rivers are often abbreviated as ARs.

With their capacity to deliver extreme precipitation and impact water resources, atmospheric rivers remain a key focus of climate research and weather forecasting. Understanding ARs is crucial for preparing for floods, snowmelt events, and water management in vulnerable regions.

AP