NASA has published the results of a study that used satellite observations to look at the locations where human activity is changing freshwater sources. The study also looked at the cause of that change. The study found that Earth’s wet land areas are getting wetter and dry areas are getting drier due to several factors. Those factors include human water management, climate change, and natural cycles.
The team was led by Matt Rodell from the Goddard Space Flight Center and used 14-years of observations from the Gravity Recovery and Climate Experiment (GRACE) spacecraft. NASA also used data on precipitation from the Global Precipitation Climatology Project, Landsat imagery, irrigation maps, and published reports on human activity related to mining and reservoir operations.
Freshwater can be found in lakes, rivers, soil, snow, groundwater, and ice. The researchers say that they are witnessing a major hydrologic change with a distinct pattern of wet lands getting wetter and dry areas getting dryer. The dry areas specifically were found to have multiple hotspots resulting from groundwater depletion.
Some of the water loss in certain regions, such as the melting of ice sheets and alpine glaciers is driven by a warming climate. The pair of GRACE satellites were launched in 2002 as a joint mission with NASA and the German Aerospace Center (DLR). There are two satellites because the precisely measured distance between the two spacecraft allows the detection of changes in the gravity field caused by movements of mass on Earth.
The study found that Southwestern California lost four gigatons of freshwater per year during study period. A gigaton is enough water to fill 400,000 Olympic swimming pools. Downward trends in freshwater were also seen in Saudi Arabia that reflects agriculture; between 2002 and 2016 that region lost 6.1 gigatons yearly of stored groundwater. The study also found areas of significant gains with the African western Zambezi basin and Okavango Delta having show an increase in freshwater at the rate of 29 gigatons per year.