Climate change is amplifying the global water cycle, or the constant movement of freshwater between clouds, land, and ocean, and it is doing so much faster than expected.
Rising global temperatures, as researchers warn in a study published in the journal ‘Nature,’ have made this system more extreme: water is moving from dry to wet regions, exacerbating droughts in some parts of the world while intensifying rainfall events and floods in others. In other words, wet areas are becoming wetter while dry areas are becoming drier.
Until now, changes in the cycle have been difficult to observe directly because the ocean accounts for roughly 80% of global precipitation and evaporation.
However, a new study led by the University of New South Wales (UNSW) in Australia used changing salt patterns in the ocean to estimate how much freshwater has moved from the equator to the poles since 1970.
The findings show that two to four times more freshwater has moved than climate models predicted, providing insight into how the global water cycle is expanding in general.
“We already knew from previous work that the global water cycle was intensifying,” says Dr. Taimoor Sohail, a mathematician and postdoctoral research associate at UNSW Science, “but we didn’t know how much.” We just didn’t know by how much.
He recalls that “the movement of freshwater from warm to cold areas constitutes the vast majority of water transport.” “Our findings provide insight into the major changes occurring in the global water cycle,” he says.
The findings show that two to four times more freshwater has been displaced than climate models predicted.
The researchers arrived at their conclusions after analyzing observations from three historical data sets spanning the years 1970 to 2014. However, rather than focusing on direct observations of precipitation, which can be difficult to measure across the ocean, they concentrated on a more unusual aspect: how salty the water was in each area of the ocean.
“In warmer regions, evaporation removes fresh water from the ocean, leaving salt behind, making the ocean saltier,” co-author Jan Zika, an associate professor in UNSW’s School of Mathematics and Statistics, explains. The water cycle transports that fresh water to cooler areas where it falls as rain, diluting the ocean and making it less salty.”
In other words, the water cycle leaves a trace in the salt pattern of the ocean, and by measuring these patterns, researchers can track how the cycle changes over time.
Between 1970 and 2014, the team estimates that between 46,000 and 77,000 cubic kilometers more freshwater was transported from the equator to the poles than expected – that’s between 18 and 30 centimeters of freshwater from tropical and subtropical regions, or roughly 123 times the water in Sydney Harbor.
“Changes in the water cycle can have serious consequences for infrastructure, agriculture, and biodiversity,” Dr. Sohail says. As a result, it is critical to comprehend how climate change affects the water cycle now and in the future. This discovery helps us understand how much this part of the water cycle is changing and can help us improve future climate change models.”
When Sohail and his colleagues compared their findings to those of 20 different climate models, they discovered that all of the models understated the actual change in the transfer of warm and cold freshwater. As a result, he believes the findings indicate that we are underestimating the effects of climate change on precipitation.
“Discoveries like ours are how we improve these models,” he emphasizes. Each new generation of models compares previous models to real-world data, identifying areas for improvement in future models. This is a normal progression in climate modeling.”
Scientists are now using the sixth generation of climate models (known as the Sixth Climate Model Intercomparison Project, or “CMIP6”), which includes updates from the fifth generation. This new discovery exemplifies the scientific process at work and has the potential to improve future estimates.
“By establishing the change in freshwater transport from warm to cold,” Sohail says, “we can move forward and continue to make these important projections about how climate change may affect our global water cycle.” Scientists will be able to use this baseline in 10 to 20 years to determine how much these patterns change over time.”
Article Author Gerluxe