Atmospheric rivers, powerful currents of water vapor suspended in the atmosphere, have been moving in unexpected ways for several decades, changing precipitation patterns and climate on a global scale.
What is an atmospheric river?
THE atmospheric rivers are vast streams of water vapor that circulate in the atmosphere and carry amounts of moisture comparable to the largest rivers on land, such as the Mississippi. These celestial rivers can extend several thousand kilometers long and up to a few hundred kilometers wide, concentrating moisture in narrow bands of the atmosphere.
These atmospheric structures play an essential role in the redistribution of water around the planet. Indeed, they capture moisture above tropical oceans and transport it to land regions located at higher latitudes. When these moisture flows come into contact with a natural barrier such as a mountain range or coastal area, they condense and then release their moisture in the form of rain or snow. By acting as a natural pump, atmospheric rivers not only contribute to nourishing soils and rivers, but also influence local ecosystems and agricultural practices, while regulating groundwater levels and the resources available to inhabitants.
Due to their major impact on the distribution of precipitation, a change in their trajectory or intensity could have profound consequences on ecosystems and the societies that depend on them, which brings us back to this study.
An unexpected change of trajectory
In recent work, researchers at the University of California, Santa Barbara analyzed data from the last forty years and observed a shift of these rivers towards the poles of approximately six to ten degrees in each hemisphere. This means that the areas usually crossed by these water vapor currents are now located further north in the northern hemisphere and further south in the southern hemisphere.
Scientists believe that the cooling of the eastern tropical Pacific, observed over the same period, could be one of the causes of this shift, although the precise mechanisms behind this phenomenon still remain largely unknown.
What impacts for our climate?
The change in trajectory of atmospheric rivers could have profound effects on global precipitation patterns. By shifting their paths towards the poles, regions traditionally supplied with water by these structures could experience a decrease in precipitation, while other regions further north or south could see their precipitation increase significantly.
The effect of these atmospheric rivers is also not limited to land: the researchers indicate that these changes could also modify the oceans. The redistribution of precipitation and air currents could notably affect water temperature and ocean currents which play a key role in regulating the global climate. This could have unforeseen impacts on marine biodiversity and even terrestrial ecosystems that rely on ocean currents for their local climate.
This change in the trajectory of atmospheric rivers is a complex and still largely unknown phenomenon. Researchers are still working to understand the causes and long-term consequences. Studying the behavior of these structures will be essential to better anticipate climate variations and prepare communities for the impacts of this movement.
Atmospheric rivers and the carbon cycle
Atmospheric rivers don't just transport moisture; they also influence the carbon cycle significantly. By promoting precipitation in certain regions, they stimulate the growth of plants, which absorb carbon dioxide from the atmosphere. However, in areas where this precipitation decreases due to changes in trajectory, ecosystems could become fragile, limiting their capacity to capture carbon. This complex interaction between atmospheric rivers and the carbon cycle highlights their role in climate balances, making their study all the more crucial at a time when global warming is disrupting these dynamics.
The study is published in the journal Science Advances.
