There have been significant declines in the amount of freshwater recorded in various hotspots around the world during the 21st century, NASA satellite observations have found.
This is thought to be due to a variety of possible factors, including human water management systems, climate change and natural cycles, although it is not entirely clear what is causing the apparent trends.
Southwestern California lost four gigatons of freshwater per year between 2007 and 2015 – with one gigaton able to fill 400,000 Olympic swimming pools – while Saudi Arabia lost 6.1 annually between 2002 and 2016.
The researchers noted that the earth’s wet land areas are getting wetter, while dry areas are getting drier, with some regions’ water supplies relatively stable while others are not.
“What we are witnessing is major hydrologic change,” said Jay Famiglietti, study co-author and researcher at NASA’s Jet Propulsion Laboratory. “Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion.”
The first-of-its-kind study took data from NASA’s Gravity Recovery and Climate Experiment (GRACE) tracking freshwater trends between 2002 and 2016 across the globe.
Although water loss and gains in some regions were concluded to be the result of a warming climate, such as where ice sheets and alpine glaciers melt, others are thought to be due to natural cycles.
Water storage was found to have increased by an average rate of 29 gigatons per year between 2002 and 2016 in Africa’s western Zambezi basin and Okavango Delta, which followed two decades of dryness.
While the Xinjiang province in China experienced an annual 5.5 gigaton loss in terrestrial water storage in the first decades of this century, despite increased surface water caused by a climate change-induced glacier melt.
The Intergovernmental Panel on Climate Change has predicted that wet areas would become wetter and dry ones drier, although it is thought to be too soon to know the reasons behind the latest findings.
“We’ll need a much longer dataset to be able to definitively say whether climate change is responsible for the emergence of any similar pattern in the GRACE data,” Famiglietti added.
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