India is among the world's major hotspots which has seen a serious decline in the availability of freshwater due to overuse of water resources, reveals a new study that combined an array of NASA satellite observations of Earth with data on human activities.
The study, published in the journal Nature, found that Earth's wetland areas are getting wetter and dry areas are getting drier due to a variety of factors, including human water management, climate change and natural cycles.
Areas in northern and eastern India, the Middle East, Australia and the US state of California are among the major areas where overuse of water resources has led to a serious decline in the availability of freshwater, the Guardian reported this week citing the study.
Without corrective actions by the governments to preserve water, the situation is likely to worsen in these areas, it added.
The first-of-its-kind study used 14 years of observations from the US/German-led Gravity Recovery and Climate Experiment (GRACE) spacecraft mission to track global trends in freshwater in 34 regions around the world.
"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 of NASA's Goddard Space Flight Center in Greenbelt, Maryland,
"A key goal was to distinguish shifts in terrestrial water storage caused by natural variability – wet periods and dry periods associated with El Nino and La Nina, for example – from trends related to climate change or human impacts, like pumping groundwater out of an aquifer faster than it is replenished," Rodell added.
Freshwater is found in lakes, rivers, soil, snow, groundwater and ice. Freshwater loss from the ice sheets at the poles – attributed to climate change – has implications for sea level rise.
On land, freshwater is one of the most essential of Earth's resources, for drinking water and agriculture.
The researchers found that while some regions' water supplies are relatively stable, others experienced increases or decreases.
"What we are witnessing is major hydrologic change," said co-author Jay Famiglietti of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
"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 dryer. Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion," Famiglietti warned.
One of the biggest causes of groundwater depletion across the board was agriculture, which can be complicated by natural cycles as seen in California, Famiglietti said.
Decreases in freshwater caused by the severe drought from 2007 to 2015 were compounded by groundwater withdrawals to support the farms in the state's Central Valley.
Southwestern California lost four gigatons of freshwater per year during the same period. A gigaton of water is the equivalent of the mass of water in 400,000 Olympic swimming pools.
Downward trends in freshwater seen in Saudi Arabia also reflect agricultural pressures, the study said.
From 2002 to 2016, the region lost 6.1 gigatons per year of stored groundwater.
The study also showed that previously undocumented water declines occurred in northwestern China's Xin Jiang province.
Famiglietti noted that while water loss in some regions, like the melting ice sheets and alpine glaciers, is clearly driven by warming climate, it will require more time and data to determine the driving forces behind other patterns of freshwater change.
The GRACE satellite observations alone could not tell the researchers what was causing the apparent trends.
"We examined information on precipitation, agriculture and groundwater pumping to find a possible explanation for the trends estimated from GRACE," said co-author Hiroko Beaudoing of Goddard and the University of Maryland in College Park.