Why you should care
Because water insecurity may be coming sooner than we think.
Cape Town was in danger this year of becoming the first big city to run out of water, which forced the South African metropolis to impose severe water-saving measures to avert “Day Zero.”
New satellite data on freshwater reserves reveal that dozens of regions across the globe are in danger of becoming the next Cape Town.
Research from scientists at NASA and the Jet Propulsion Laboratory in Pasadena, California, shows that worldwide freshwater reserves have changed drastically since 2002. The decline in water availability in regions such as northern India, northeast China, the Caspian Sea and across the Middle East has been blamed mainly on irrigation and groundwater pumping.
“Any of these spots on the map are potential ‘Cape Towns’ in future,” says Jay Famiglietti, one of the authors of the study, referring to the 34 areas that showed the greatest changes. “Freshwater availability is changing, and water insecurity is much closer than we think.”
The paper, to be published in the journal Nature, is the first to use gravitational satellite data to map global trends in freshwater availability across a 14-year period, drawing on data from NASA’s Grace satellites.
The research identifies areas where water resources rose or fell significantly during the period and identifies 14 regions where changes were primarily due to human activity, compared with eight regions where the changes were mainly caused by climate.
“The human impact has been far, far greater than we ever anticipated,” says Famiglietti. “The human fingerprint is all over that freshwater availability map and we need to deal with it.”
Irrigation for farmland was the biggest single user of freshwater, and the study showed stark declines in highly irrigated areas such as northern India.
The changing water patterns are creating great disparities in water availability, Famiglietti points out, with dramatic declines in some areas and unusual increases in others, which could make them vulnerable to flooding.
Regions such as western Brazil, the Okavango Delta in Botswana and the northern plains of North America all saw significant increases in freshwater storage during the period. Prolonged droughts in California, eastern Brazil and the Middle East led to depleted groundwater reserves.
The more vulnerable regions are the ones where people don’t have access to multiple sources of water.
Matthew Rodell, hydrologist, NASA
The study uses gravitational satellites to solve a problem that has long perplexed hydrologists: how to measure accurately the water that is hidden underground, particularly across a large area such as a continent.
Gravitational satellites do not take images. Instead they measure differences in the gravitational pull of the Earth, which can be affected by the presence of water. “The largest changes we see anywhere are the ice sheet and glacier losses, those are the fastest rates of change,” says Matthew Rodell, lead author on the report and a hydrologist at NASA. “But that is not typically water you would use for drinking or agriculture.”
Melting ice caused big drops in freshwater storage in Antarctica, Greenland, Alaska and Patagonia, mainly due to climate change.
Rodell declines to identify any single region most likely to encounter a “Day Zero” shortage like Cape Town’s, but says that careful water management is crucial to combating shortages. “Almost any region can be affected by a drought, but the more vulnerable regions are the ones where people don’t have access to multiple sources of water,” he says.
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