NASA says the world’s critical freshwater resources have been “abruptly” depleting over the past decade.
Billions of people rely on freshwater sources for drinking water and power generation. Around the world, 70 percent is used for agriculture. At least 10 percent of animals live exclusively in freshwater environments. More than a decade ago, scientists warned shortages would affect more than half its future population by 2050 if governments failed to act.
The loss of freshwater may signify a shift, indicating Earth’s continents have entered a persistently drier phase. An international team of scientists identified the depelation using NASA-German Gravity Recovery and Climate Experiment satellites.
By analyzing the data they collected from their observations, they found evidence of the abrupt drop in May 2014. From 2015 through last year, measurements showed that the average amount of freshwater on land was 290 cubic miles lower than average levels between 2002 and 2014.
“That’s two and a half times the volume of Lake Erie lost,” Matthew Rodell, a hydrologist at the agency’s Goddard Space Flight Center, said in a statement.
The Great Lakes-St. Lawrence River Basin is the largest watershed in the world, containing more than 20 percent of the world’s supply of surface fresh water and around 84 percent of North America’s surface fresh water.
Rodell and others published their findings in the journal Surveys in Geophysics.
The satellites measure fluctuations in Earth’s gravity on a monthly time scale, revealing changes in water mass both on and under the ground.
The decline reported in the study began with widespread drought in Brazil that was followed by other major droughts in the Americas, Europe, Africa, and Australasia. They noted that one of the most El Niño events since 1950 - a climate pattern that causes the Pacific jet stream to shift south and east, leading to warmer and drier conditions in the northern US - altered weather and rainfall patterns around the world in the mid-2010s.
Even after the pattern ended, global freshwater did not rebound, and 13 of the world’s most intense droughts observed by the satellites have occurred since January 2015.
Climate change may be contributing to this depletion, although it is difficult to definitively link the drop in freshwater to global warming, as there are uncertainties in climate projections. Climate change results in more extreme weather events. Long stretches between intense precipitation allows soil to dry and become more compact, lessening the amount of water it is able to absorb when it does rain.
“The problem when you have extreme precipitation,” NASA Goddard meteorologist Michael Bosilovich said, “is the water ends up running off,” instead of soaking in and replenishing groundwater stores.
“Warming temperatures increase both the evaporation of water from the surface to the atmosphere, and the water-holding capacity of the atmosphere, increasing the frequency and intensity of drought conditions,” he noted.
This year is forecast to be Earth’s warmest on record, and much of the US has been in drought conditions over the last few months.
Rodell noted the nine warmest years in the modern temperature record coincided with the decline.
“We don’t think this is a coincidence, and it could be a harbinger of what’s to come.”
