Nav: Home

Satellite study finds major shifts in global freshwater

May 16, 2018

A new global, satellite-based study of Earth's freshwater distribution found that Earth's wet areas are getting wetter, while dry areas are getting drier. The data suggest that this pattern is due to a variety of factors, including human water management practices, human-caused climate change and natural climate cycles.

The NASA-led research team, which included Hiroko Beaudoing, a faculty specialist at the University of Maryland's Earth System Science Interdisciplinary Center (ESSIC), used 14 years of observations from the Gravity Recovery and Climate Experiment (GRACE) mission to track global trends in freshwater in 34 regions around the world.

The study, published in the May 17, 2018 issue of the journal Nature, also incorporated satellite precipitation data from the ESSIC-led Global Precipitation Climatology Project; Landsat imagery from NASA and the U.S. Geological Survey; irrigation maps; and published reports of human activities related to agriculture, mining and reservoir operations. The study period spans from 2002 to 2016.

"This is the first time we've assessed how freshwater availability is changing, everywhere on Earth, using satellite observations," said Matt Rodell, lead author of the paper and chief of the Hydrological Sciences Laboratory at NASA's Goddard Space Flight Center. "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."

Freshwater is present in lakes, rivers, soil, snow, groundwater and glacial ice. Its loss in the ice sheets at the poles--attributed to climate change--has implications for sea level rise. On land, it is one of Earth's most essential resources for drinking water and irrigation. While some regions' water supplies are relatively stable, others normally experience increases or decreases. But the current study revealed a new and distressing pattern.

"What we are witnessing is major hydrologic change," said co-author James Famiglietti of NASA's Jet Propulsion Laboratory. "We see, for the first time, a very 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 noted that while water loss in some regions is clearly driven by warming climate, such as the melting ice sheets and alpine glaciers, it will take more time before other patterns can be unequivocally attributed to climate change.

"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," Famiglietti said. "However, the current trajectory is certainly cause for concern."

The twin GRACE satellites, launched in 2002 as a joint mission with the German Aerospace Center (DLR), precisely measured the distance between the two satellites to detect changes in Earth's gravity field caused by movements of mass on the planet below. Using this method, GRACE tracked variations in terrestrial water storage on monthly to yearly timescales until its science mission ended in October 2017.

However, the GRACE satellite observations alone couldn't tell Beaudoing, Rodell, Famiglietti and their colleagues what was causing an apparent trend.

"We examined information on precipitation, agriculture and groundwater pumping to find a possible explanation for the trends estimated from GRACE," said Beaudoing, who also has a joint appointment at NASA Goddard.

One of the big 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 4 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. A majority of California's freshwater comes in the form of rainfall and snow that collects in the Sierra Nevada as snowpack and then is managed through a series of reservoirs as it melts. When natural cycles led to dry years, causing diminished snowpack and surface waters, people relied on groundwater more heavily.

Downward trends in freshwater seen in Saudi Arabia also reflect agricultural pressures. From 2002 to 2016, the region lost 6.1 gigatons per year of stored groundwater. Imagery from the Landsat series of satellites shows the growth of irrigated farmland in the arid landscape from 1987 to the present, which explains the increased drawdown.

Natural cycles of rainy and dry years can also cause a trend in the 14-year data record that is unlikely to persist, Rodell said. An example is the western Zambezi basin and Okavango Delta, a vital watering hole for wildlife in northern Botswana. In this region, terrestrial water storage increased at an average rate of 29 gigatons per year from 2002 to 2016. This wet period during the GRACE mission followed at least two decades of dryness. Rodell believes this is a case of natural variability that occurs over decades in this region of Africa.

The researchers found that a combination of natural and human pressures can lead to complex scenarios in some regions. Previously undocumented water declines occurred in northwestern China in Xin Jiang province. This region, about the size of Kansas, is bordered by Kazakhstan to the west and the Taklamakan desert to the south and encompasses the central portion of the Tien Shan Mountains.

Rodell and his colleagues had to piece together multiple factors to explain the disappearance of 5.5 gigatons of terrestrial water storage per year in Xin Jiang Province. Less rainfall was not the culprit. Additions to surface water were also occurring from climate change-induced glacier melt and the pumping of groundwater out of coal mines. But these additions were more than offset by depletions caused by an increase in water consumption for the irrigation of cropland and evaporation of river water from the desert floor.

The successor to GRACE, called GRACE Follow-On, a joint mission with the German Research Centre for Geosciences (GFZ), is at Vandenberg Air Force Base in California undergoing final preparations for launch.
-end-
This release was adapted from text provided by NASA's Goddard Space Flight Center.

The research paper, "Emerging Trends in Global Freshwater Availability," Matthew Rodell, James Famiglietti, David Wiese, J.T. Reager, Hiroko Beaudoing, Felix Landerer and Min-Hui Lo, was published in the journal Nature on May 17, 2018.

This work was supported by NASA, the University of California Office of the President and the Ministry of Science and Technology, Taiwan. The content of this article does not necessarily reflect the views of these organizations.

Media Relations Contact: Matthew Wright, 301-405-9267, mewright@umd.edu

University of Maryland
College of Computer, Mathematical, and Natural Sciences
2300 Symons Hall
College Park, MD 20742
http://www.cmns.umd.edu?@UMDscience

About the College of Computer, Mathematical, and Natural Sciences

The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.

University of Maryland

Related Climate Change Articles:

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
Historical climate important for soil responses to future climate change
Researchers at Lund University in Sweden, in collaboration with colleagues from the University of Amsterdam, examined how 18 years of drought affect the billions of vital bacteria that are hidden in the soil beneath our feet.
Can forests save us from climate change?
Additional climate benefits through sustainable forest management will be modest and local rather than global.
From crystals to climate: 'Gold standard' timeline links flood basalts to climate change
Princeton geologists used tiny zircon crystals found in volcanic ash to rewrite the timeline for the eruptions of the Columbia River flood basalts, a series of massive lava flows that coincided with an ancient global warming period 16 million years ago.
Think pink for a better view of climate change
A new study says pink noise may be the key to separating out natural climate variability from climate change that is influenced by human activity.
Climate taxes on agriculture could lead to more food insecurity than climate change itself
New IIASA-led research has found that a single climate mitigation scheme applied to all sectors, such as a global carbon tax, could have a serious impact on agriculture and result in far more widespread hunger and food insecurity than the direct impacts of climate change.
More Climate Change News and Climate Change Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.