Atmospheric Rivers Map in South America Reveals Rainfall Origins

What if part of the water that falls on South America had traveled through a vast invisible network, high above forests and mountains? A new map shows how these “air rivers” move moisture across a continent.

Rivers Without Banks Travel Across the South American Sky for Thousands of Kilometers

There is no valley, no valley carved into rock. Yet, real highways of water vapor traverse the atmosphere of South America continuously. Researchers call them “air rivers.” Essentially, they are corridors where moisture moves preferentially over long periods, before sometimes falling far from its point of origin.

A study published in August 2026 in Nature Communications now provides a continent-scale map. Unlike the classic atmospheric rivers, which are brief weather phenomena, these networks describe persistent moisture circulations. They emerge from the cumulative analysis of numerous weather situations observed over time.

Researchers Have Reconstructed a Real Map of the Sky’s Watersheds

To trace a water that is impossible to observe like a conventional river, scientists combined climate data and mathematical modeling. They then analyzed 724 zones across South America to identify land areas that feed the moisture that later returns to Earth as rain.

The process resembles an inverted watershed. On the ground, rivers collect water and deliver it downstream. In the sky, evapotranspiration fuels the system, while winds carry moisture over long distances. Finally, precipitation acts as the outlet, thus closing a continuous cycle between forests, soils and oceans.

This new map also reveals a crucial point: not all moisture sources exert the same impact. The researchers identified tipping points. Beyond certain thresholds, adding more territory hardly yields additional moisture. This result, though technical, helps target more precisely the zones whose protection genuinely influences rainfall elsewhere.

When a Forest Disappears, the Tap Can Also Shut Off Much Farther Away

This is where the phenomenon becomes particularly tangible. An Amazon rainforest tree does not merely use water from the soil. On the contrary, it returns a portion of it to the atmosphere through transpiration. This moisture recycled by vegetation can then travel, form clouds, and feed rains sometimes located at great distances.

Studies published in 2026 in Nature Geoscience show that deforestation durably disrupts evapotranspiration of South American ecosystems. Moreover, its effects linger about 21 to 22% longer than those of a fire or an isolated drought. Gradually, this weakens the exchanges of water between vegetation and the atmosphere.

The Ucayali basin in Peru perfectly illustrates this challenge. According to estimates cited in the study, deforestation of certain upstream zones of the atmospheric flows could reduce annual rainfall by 5 to 13%. At first glance, the figure seems modest, but in reality its effects can profoundly transform local ecosystems.

In Peru, a Few Percent of Rain Lost Could Upend Ground Rivers

With less water falling from the sky, annual runoff could drop by 19 to 50%. This amplification clearly shows that a hydrological system does not always respond in a linear fashion. Thus, small variations in rainfall are enough to substantially alter river discharges, soil moisture, and available resources.

The paradox is striking. Indeed, protecting the water of a region may depend on forests located hundreds of kilometers away, sometimes even in another country. A study published in PNAS reminds us that humidity recycled in the Amazon influences water resources across large swaths of the continent, far beyond its own territory. The researchers now plan to extend this method to other regions of the world.

Thus, water management would no longer rely solely on dams, aquifers, or visible basins. It would also integrate the invisible basins of the atmosphere, which would profoundly change the way we read hydrological maps. Ultimately, some essential rivers could continue to exist without ever appearing on traditional maps, while shaping a large portion of terrestrial rainfall.