Freshwater hotspots around the world are in danger, NASA finds

NASA has pinpointed hotspots around the world where freshwater supplies are in danger through one-of-a-kind study using satellites.

Groundwater is a primary source of fresh water in many parts of the world. Some regions are becoming overly dependent on it, consuming groundwater faster than it is naturally replenished and causing water tables to decline unremittingly.

Scientists found this out by combining multiple NASA satellite observations of Earth with data on human activities to map locations where freshwater is changing around the world to determine why.

"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 Matt Rodell with NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

He led a team which used 14 years of observations from the U.S. and German-led Gravity Recovery and Climate Experiment (GRACE) spacecraft mission to track global trends in freshwater in 34 regions around the world.

The study, published in the journal Nature, shows that Earth’s wet land areas are getting wetter and dry areas are getting drier due to an array of factors that include climate change, human water management and natural cycles.

"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," Rodell said.

They observed satellite precipitation data from the Global Precipitation Climatology Project, NASA and U.S. Geological Survey imagery and irrigation maps.

Through looking at data the scientists were able to get a full understanding of the reasons for Earth’s freshwater changes as well as the sizes of those trends.

"What we are witnessing is major hydrologic change," said co-author Jay Famiglietti of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Areas in northern and eastern India, the Middle East, California and Australia are among the hotspots where overuse of water resources has caused a serious decline in the availability of freshwater, and problems are already occurring.

"We see a distinctive pattern of the wet land areas of the world getting wetter – those are the high latitudes and the tropics – and the dry areas in between getting drier. Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion," Famiglietti said.

They examined information on precipitation, agriculture and groundwater pumping to find a possible explanation for the trends estimated from GRACE, but according to Famiglietti, they will need to see more data.

"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 data-set to be able to definitively say whether climate change is responsible for the emergence of any similar pattern in the GRACE data," Famiglietti said.

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