Scientists map South America's aerial rivers for the first time — they drive rainfall across the continent

An international team of researchers has for the first time systematically mapped the aerial rivers over South America — stable atmospheric currents of water vapor that shape rainfall patterns across much of the continent. The findings were published in Nature Communications on August 7, 2026.

Aerial rivers are persistent corridors in the atmosphere through which moisture travels from oceans deep into the continents. The vapor originates from evaporation over the sea surface, soil, and tree foliage. Over South America, these invisible flows largely determine how much rain falls in the Amazon basin, on the Andean slopes, and in the Argentine pampas. In the new study, scientists presented a complete map of such currents: their sources, trajectories, and the zones where moisture falls as precipitation.

The authors identified four modes of aerial river behavior over the continent. The first mode describes entry points — vapor-saturated flows arriving from ocean coasts. The second covers zones of active discharge, where moisture is heavily consumed by rainfall. The third corresponds to areas of sharp deceleration, where the air is already depleted of moisture and regions must rely on local evaporation. The fourth mode applies to the driest territories, which aerial rivers barely reach.

Beyond classification, the researchers identified critical catchment basins in the upper reaches — key areas that feed aerial rivers with evaporation. They also marked "tipping points": thresholds beyond which the contribution of these basins to moistening downstream regions drops sharply. Many of the most important basins do not align with administrative or geographic boundaries, prompting the authors to stress that effective management requires institutional cooperation.