Freshwater around the world is dramatically moving away from its usual location, shifting from warmer regions to colder regions – implying that some major transition is happening at a global level when it comes to the long-established water cycle.
Clouds, precipitation, rivers, and seas. This is the water cycle: the motions of water around our planet, crucial to life on Earth.
It is not surprising that the human-made climate crisis is changing it – what has caught scientists by surprise is this is happening much faster than models had predicted. Comparison to 20 different climate models shows that they all underestimated the breadth of this change.
As reported in the journal Nature, at least two times more freshwater has moved from warmer to colder areas worldwide than our climate models predicted. The estimation was performed by studying the salt concentration in the ocean, providing a view of how sizable the change is.
“We already knew from previous work that the global water cycle was intensifying,” lead author Dr Taimoor Sohail, from the University of New South Wales, said in a statement. “We just didn't know by how much.
“The movement of freshwater from warm to cold areas forms the lion’s share of water transport. Our findings paint a picture of the larger changes happening in the global water cycle.”
The salinity approach gives an idea of the water cycle with a broader view. After all, 80 percent of rainfall and evaporation happens over the ocean. Data collected between 1970 and 2014 showed a reduction in salinity in the ocean water at higher latitudes.
"In warmer regions, evaporation removes fresh water from the ocean leaving salt behind, making the ocean saltier,” added co-author Professor Jan Zika, also at the University of New South Wales. “The water cycle takes that fresh water to colder regions where it falls as rain, diluting the ocean and making it less salty.”
The study estimate that during the 44 years in question, between 77,000 and 46,000 cubic kilometers of freshwater has shifted from tropical and subtropical regions towards the poles. That would be equivalent to covering the whole of the United States in something like 8 to 5 meters (315 to 188 inches) of water.
“Changes to the water cycle can have a critical impact on infrastructure, agriculture, and biodiversity,” continued Dr Sohail. “It’s therefore important to understand the way the climate change is impacting the water cycle now and into the future."
“This finding gives us an idea of how much this limb of the water cycle is changing, and can help us improve future climate change models.”
The team expects that the work will inform models and be used in future estimations of how much the water cycle is shifting.
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