An ambitious study of the state of Earth’s freshwater sources has concluded that dry regions have gotten dryer and wet regions have gotten wetter over the past 14 years – and yes, you can bet that we humans had a big role to play.
Decades of past research have demonstrated that the climate cycles maintaining freshwater in all its forms – flowing in lakes and rivers or stored in groundwater reservoirs and glaciers – are being disrupted by anthropogenic activities. Furthermore, large-scale water extraction and diversion operations, undertaken to meet the ever-growing demands from agriculture, industrial processes, and expanding urban populations, are depleting the planet’s stores at unsustainable rates.
Altogether, it is estimated that nearly 80 percent of the world’s population live in areas extremely threatened with impending water insecurity, and two-thirds of the world’s freshwater habitats are at risk of irrevocable change.
In order to form the most effective plans for mitigating a dystopian future, scientists need accurate assessments of the current state of freshwater. And though this can be done easily on a region-by-region basis, quantifying it on a global scale is, understandably, quite difficult.
Luckily for humanity’s sake, leaping fearlessly into massive datasets is what researchers at NASA do best.
The team’s comprehensive model, published in Nature, reviewed satellite-based precipitation observations from the Earth System Science Interdisciplinary Center’s ongoing Gravity Recovery and Climate Experiment (GRACE) mission, Earth surface images from NASA and the US Geological Survey satellites, and published reports about agricultural, mining, and hydrological operations from across the world.
Their analysis shows changes to 34 regions, covering major areas of every continent, occurring between 2002 and 2016.
"This is the first time we've assessed how freshwater availability is changing, everywhere on Earth, using satellite observations," lead author Matt Rodell said in a statement. "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.”
"What we are witnessing is major hydrologic change.”
In addition to confirming the previously identified patterns of intensified drought and flood, the results showed, unsurprisingly, that the largest freshwater fluxes happened in Antarctica, Greenland, the Gulf of Alaska coast, and Canadian archipelago; regions where global warming-driven ice melt has been most severe.
Exemplifying the lunacy of farming in naturally arid areas, the team noted that southern California and Saudi Arabia lost about 4 and 6.1 gigatons of groundwater water per year, respectively, due to extraction for farm irrigation and several droughts. It is unlikely that the levels will ever fully bounce back.
Sizable water changes were also observed in northwestern China – a net depletion – and the Okavango Delta – where a theorized multi-decade-long dry-wet pattern appears to have switched toward wet.
"The pattern of wet-getting-wetter, dry-getting-drier is predicted by the Intergovernmental Panel on Climate Change models for the end of the 21st century, but we'll need a much longer dataset to be able to definitively say that climate change is responsible for the emergence of a similar pattern in the GRACE data," said co-author James Famiglietti. "However, the current trajectory is certainly cause for concern."
