Scientists Uncover Vast Invisible Aerial Waterways Flowing Over South America

Researchers have unveiled an extensive network of invisible aerial waterways transporting moisture through the skies above South America. These unseen currents shuttle water vapor across the continent, influencing rainfall patterns far from any visible river channels.

Unlike the intermittent and short-lived atmospheric rivers, these aerial waterways are enduring moisture corridors shaped by a mix of wind systems, including sea breezes, low-level jets, and atmospheric rivers themselves.

Some of these aerial flows span impressive distances. Studies have previously traced moisture routes feeding rainfall in Pakistan that extend from Scandinavia all the way to Madagascar. Now, scientists have applied mathematical models and climate observations to track water vapor movements over South America—from atmospheric entry points to precipitation zones.

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Following Moisture Across the Landscape

At its core, the research aims to pinpoint the origins of atmospheric moisture and trace its journey via prevailing winds. In practice, this involves monitoring a vast, dynamic system that shifts continuously.

Scientists have identified key upwind source regions, which contribute significant moisture to downwind areas. Water enters these aerial rivers through processes such as soil evaporation and water release from vegetation, known as transpiration.

The team also mapped “turning points,” where the moisture supplied by a particular upwind source to a region suddenly diminishes. As detailed in the Nature Communications article, this approach illuminates how far moisture travels, its speed, and the rainfall it ultimately produces.

However, these aerial rivers are not static. The researchers observed that shifting wind patterns can reverse moisture flow directions toward coastal urban areas within just one day.

Classifying Four Types of Aerial Rivers

To better understand the system, the team categorized South America’s aerial rivers into four groups: G1, G2, G3, and G4. G1 zones act as the starting points, where moisture-laden air from the ocean first enters the continent. Interestingly, these regions aren’t always located directly on the coast. Next, G2 zones represent areas where atmospheric moisture can increase while some vapor is lost as it moves inland.

In G3 zones, the moisture flow dramatically slows and vapor content lessens, leaving rainfall there more reliant on evaporation from land. Several of these may lie upstream of major river systems.

G4 zones, located farthest downwind and described as atmospheric plains, receive little moisture from aerial rivers and often encompass water-stressed cities.

Deforestation Impacts Rainfall Across Distances

The researchers emphasize the critical role of forests in this hydrological cycle. Vegetation contributes moisture through transpiration, so forest loss in upwind basins can reduce water vapor transported along aerial rivers. The team points to the Peruvian Ucayali basin, where deforestation has been linked to a 5–13 percent decrease in annual rainfall and a 19–50 percent reduction in runoff via these atmospheric moisture flows.

This demonstrates why conserving and restoring forests, especially in upwind basins, is crucial. The aerial rivers also pose governance challenges, as they ignore political boundaries.

“These basins often transcend administrative and topographic boundaries,” the researchers explain. “Their effective management requires institutional collaboration among entities responsible for regional governance.”

The methodologies from this study can be adapted to analyze aerial rivers and their moisture sources in other regions worldwide.

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