May 16, 2018 - Energy & Environment

First map of global freshwater trends shows "human fingerprint"

Adapted from M. Rodell et al., 2018, based on data from Gravity Recovery and Climate Experiment satellites; Map: Harry Stevens / Axios.

New research from NASA finds that human activities, including causing global warming and depleting groundwater for agriculture, are making for an increasingly water-stressed world. It's the first global accounting of trends in freshwater availability.

"No national, regional, or local water plan or assessment should overlook these estimates - they are the boundary conditions that shape water security."
— Marc Levy, a researcher at Columbia University's Earth Institute who was not involved in the new study

The big picture: Since 2002, a pair of NASA satellites has been taking precise measurements of changes in the Earth's gravitational field. The mission known as GRACE (short for Gravity Recovery and Climate Experiment) has allowed scientists to detect trends in ice sheet thickness, surface water depth, and groundwater depletion.

What they found: The study, published in the journal Nature on Wednesday, provides reasons to worry about the stability of parts of the globe, particularly the heavily populated Middle East and South Asia. “This is the first time we’ve ever had a global map of how freshwater availability is changing,” said lead author Matthew Rodell of NASA's Goddard Space Flight Center. He said the results show a "clear human fingerprint" on global freshwater availability.

What's happening: Of the 34 areas with prominent changes in freshwater availability, 8 of them were found to be due to climate change, and 14 were from other human activities, such as sucking groundwater out of aquifers for crops. Just 12 of the 34 areas were deemed to be due to natural variability alone.

Water winners and losers:

  • Hot spots of water loss include the Greenland and Antarctic Ice Sheets, which are losing mass as the world warms, the Middle East and South Asia, where drought and groundwater depletion have raised fears of conflicts, and the Southwest U.S.
  • The Greenland Ice Sheet alone lost about 279 billion tons of freshwater per year between April 2002 and March 2016, the study found.
  • During the same period, the northern Middle East, including Syria and Iran, lost 32.1 billion tons of freshwater.
  • The researchers found gains in freshwater availability associated with dam projects in South America and China, as well as increases in parts of North America.
  • Those findings are consistent with climate projections showing that higher latitudes will get wetter while mid-latitudes and the tropics see less precipitation.

What it means: Scientists and policy experts say these findings have profound implications for the future of food availability, since so much water goes toward agriculture. “We need to remember that it’s not just water, it’s also water in food, in energy, in people,” said Jay Famiglietti, a study coauthor and researcher at NASA's Jet Propulsion Laboratory.

  • Experts in the security implications of climate change, including water availability, said the new study could be viewed as a map of potential future conflict, if cooperation to ensure adequate water supplies fails.

"“Some of the trends outlined in this study should raise red flags for policy-makers," said Caitlin Werrell, co-founder of The Center for Climate and Security, in an email. Werrell was not involved in the new study.

Coming soon: The GRACE satellites used for this study are no longer functional, but NASA is scheduled to launch a GRACE follow-on mission on May 22. The new satellites will allow researchers to extend their data records to 30 years, which is considered long enough to detect and attribute climate trends. It will also have slightly higher resolution, enabling more close-ups of water-stressed regions.

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