- Humans have drastically altered the global water landscape in profound way, the study finds.
- As a result, some places are getting wetter and other areas are drying out.
The location of fresh water around the world is continually changing, and humans are the driving force behind the moves, according to a new study by NASA scientists.
As a result, some places are getting wetter and other areas are drying out.
“The human fingerprint is all over changing freshwater availability. We see it in large-scale overuse of groundwater. We see it as a driver of climate change,” said Jay Famiglietti, a co-author of the research who is the senior water scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. “The study shows that humans have really drastically altered the global water landscape in a very profound way.”
Using NASA satellites and data on human activities to map locations where freshwater is changing around the globe, researchers found that there are several factors involved in the shifts, including water management practices, climate change and natural cycles. The study was published Wednesday in the journal Nature.
Researchers, led by Matt Rodell of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, tracked global trends in freshwater in 34 regions, or hotspots, around the world using 14 years of observations from the Gravity Recovery and Climate Experiment (GRACE) spacecraft mission.
Theys combined this information with satellite precipitation data from the Global Precipitation Climatology Project, Landsat imagery from the U.S. Geological Survey and NASA, irrigation maps and published reports of human activities related to agriculture, mining and reservoir operations.
"This is the first time that we’ve used observations from multiple satellites in a thorough assessment of how freshwater availability is changing, everywhere on Earth," said Rodell. "A key goal was to distinguish shifts in terrestrial water storage caused by natural variability – wet periods and dry periods associated with El Niño and La Niña, for example – from trends related to climate change or human impacts, like pumping groundwater out of an aquifer faster than it is replenished."
At least 40 percent of 34 hotspots studied around the world can be linked to human water management activities, such as excessive groundwater pumping for farming. This includes areas including northern India, the North China Plain and parts of Saudi Arabia.
Meanwhile, the shifts in eight regions can be linked to climate change, while the shifts in the remaining 12 regions can be linked to natural factors like cyclical weather patterns, the study found.
Co-author Jay Famiglietti of NASA's Jet Propulsion Laboratory said that while water loss in some regions is clearly driven by a warming climate, it "will require more time and data to determine the driving forces behind other patterns of freshwater change."
"The pattern of wet-getting-wetter, dry-getting-drier during the rest of the 21st century is predicted by the Intergovernmental Panel on Climate Change models, but 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," he said.
Depletion of fresh groundwater in some regions is not limited to excessive pumping but can also be exacerbated by cycles of persistent drought or rainy conditions, researchers said.
The groundwater depletion of 4 gigatons of water a year between 2002 and 2016 in California’s Central Valley is an example of decreased groundwater replenishment from rain and snowfall combined with increased pumping for agriculture, the study noted. To put it into perspective, a gigaton of water would fill 400,000 Olympic swimming pools.