Earth has experienced significant shifts in freshwater distribution across the globe thanks to climate change, water management and natural cycles, among other factors, according to a NASA study.
"What we are witnessing is major hydrologic change," said Jay Famiglietti of NASA's Jet Propulsion Laboratory in Pasadena, California. "We see a distinctive pattern of the wetland areas of the world getting wetter -- those are the high latitudes and the tropics -- and the dry areas in between getting dryer. Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion."
Researchers tracked global freshwater trends in nearly three dozen regions worldwide using 14 years of data and imagery from the Gravity Recovery and Climate Experiment (GRACE) mission, which consists of two spacecrafts orbiting Earth. They analyzed the information alongside irrigation maps, precipitation data from the Global Precipitation Climatology Project, Landsat imagery from the NASA/U.S. Geological Survey and published reports of human activity related to agriculture, mining and reservoir operations, according to a news release.
The findings of the first-of-its-kind study were published Wednesday in Nature, a scientific journal.
"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," Matt Rodell of NASA's Goddard Space Flight Center, said in the news release.
"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," he said.
In some regions, like those with melting alpine glaciers and ice sheets, climate change is a clear driver of water loss, according to Famiglietti.
Agricultural practices also have a big impact. Pumping groundwater for agriculture significantly contributed to freshwater depletion around the world during the period studied, which could explain a decline in freshwater that was observed in Saudi Arabia, for example.
Levels of groundwater are also impacted by drought cycles and persistent rain, according to NASA.