This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Water does not flow only through rivers on the ground. Vast quantities of water also move through the atmosphere, carried by winds from oceans and land before eventually falling as precipitation hundreds or even thousands of kilometers away.
These persistent pathways of atmospheric moisture are often referred to as "aerial rivers" or "flying rivers." A research team led by National Taiwan University (NTU) has shown that these invisible rivers form organized drainage systems with structures that resemble terrestrial river networks. By analyzing long-term atmospheric moisture transport across South America, the researchers identified four distinct hydrological regions within the continental aerial-river system: headwater, drainage, outfall and plain regions. The study is published in Nature Communications.
A major challenge in managing aerial rivers is determining how far upstream—or, in atmospheric terms, how far upwind—management efforts should extend. Moisture reaching a given region may originate across vast areas, but not all source regions contribute equally. Previous studies have often relied on fixed thresholds to define important source areas, making results sensitive to the threshold selected.
To address this problem, the team developed a mathematical approach for identifying a natural turning point in the relationship between the size of an upwind source area and the amount of moisture it contributes. This turning point defines a critical upwind basin, beyond which the additional land area contributes progressively less efficiently to rainfall in the target region. The results show that the location of this turning point varies substantially across South America, demonstrating that no single threshold can adequately characterize all aerial-river systems.
The findings provide a new way to think about water-resource management. Conventional approaches generally follow surface watersheds or administrative boundaries, but aerial rivers cross both. Land-use change in one region can therefore influence rainfall and water availability far downwind.
"Our earlier research showed that land-use change can affect water availability far downwind through flying rivers. What was still missing was an objective way to identify which upwind areas matter most. The turning-point approach provides a systematic method for defining these critical source regions and for exploring the factors that govern moisture drainage.
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