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| Dry, cracked Earth that used to be under Lake Mead, the largest reservoir in the United States, illustrates how water resources are shifting due to climate change and human activity. A new analysis using satellite data has identified more than 30 regions on Earth where the amount of stored water on the landscape has increased or decreased by an amount greater than the 32 billion ton storage capacity of Lake Mead. Justin Sullivan/GETTY IMAGES |
By combining 14 years’ worth of
satellite data, scientists have captured a startling portrait of the
world’s water supply undergoing rapid transformation. The new analysis
points to areas where there is increasing potential for conflict as a
growing demand for water collides with the impacts of climate change. In
Canada, the maps shows shifting water supplies that include wetter,
more flood-prone regions in many areas of the country but a general
drying out in the western sub-Arctic.
“This
is an eye-opener,” said Roy Brouwer, an economist and executive
director of the University of Waterloo’s Water Institute who was not
involved in the analysis. “It raises awareness that things are changing
and that in some areas something has to happen to counter and anticipate
some of the catastrophes that may be waiting for us in the not-so-far
future.”
The analysis is based on
data from the Gravity Recovery and Climate Experiment, or GRACE, a
NASA-led mission launched in 2002 that involved two satellites circling
the globe in tandem about 220 kilometres apart. A microwave link between
the two satellites allowed scientists to precisely monitor minuscule
changes in their separation down to a distance of 10 microns, or about
one-tenth the width of a human hair.
The
setup created a sort of flying weight scale that mean the satellites
could be used to measure slight regional variations in Earth’s
gravitational pull. Many of those variations are due to geological
features, such as mountain ranges, that do not vary over time. But by
taking measurements over many years, the satellite also picked up
changes that are largely due to the movement of massive amounts of water
at or near Earth’s surface.
Researchers
have published many results based on GRACE data but the new analysis,
published Wednesday in the journal Nature, marks the first time all
available observations from the mission, from April, 2002, to March,
2016, have been analyzed and assembled to provide a comprehensive map of
water trends around the world. Those trends encompass changes in where
water is stored across Earth’s surface, including groundwater, soil
moisture, glaciers, snow cover and surface water. The result suggests a
water landscape that is changing fast on a global scale, in large part
due to human activity and climate change.
“The
human fingerprint is all over what we see in the map,” said Jay
Famiglietti, a water-resource expert affiliated with NASA’s Jet
Propulsion Laboratory in Pasadena, Calif., and the incoming director of
the University of Saskatchewan’s Global Institute for Water Security.
Dr.
Famiglietti, a co-author on the Nature study, has played a central role
in interpreting data from the GRACE mission over its lifetime. He added
that the new analysis pointed to profound changes in the Earth’s water
resources that should serve as a wake-up call for policy makers.
“There
are implications in that map for food security, for water security and
for human security in terms of things like conflict and climate
refugees,” he said.
In total, Dr.
Famiglietti and his colleagues identified 34 regional trends in water
storage observed by GRACE. Some are likely due to natural variations
over the time that the observations were taken. For example, the Amazon
basin looks like it’s getting wetter because the area has been
recovering from a drought. The same is likely the case for a region
centred on the Canadian Prairies and parts of the United States. Over
the long term, those trends may fade away.
The
most obvious changes are clearly due to climate change and relate to
ice loss in the polar regions and in some mountainous areas such as
Alaska and the southern portions of the Andes in South America. Others
show places where humans have directly affected water storage.
One
example is a large swatch of diminishing water supply across parts of
the Middle East, including Syria and Iraq. The shortage is related to
dam building in Turkey and overuse of groundwater, both of which have
exacerbated an already complex and volatile political situation in the
region.
Similar shortfalls in India
reflect the impact of subsidized electricity, which has created a
“perverse incentive” that makes it inexpensive to pump out more
groundwater than can be replenished, said Dr. Brouwer.
Overall,
the map shows how the world’s water is increasingly moving from natural
storehouses such as glaciers to human-built reservoirs, a change that
comes with plenty of political fallout when that water crosses
international boundaries, said Aaron Wolf, an expert in water-related
conflict at Oregon State University.
“This kind of data really helps us identify hot spots in advance of real crises,” he said.
Support
for the GRACE mission officially ended last fall and the last of the
satellites burned up as its orbit decayed in mid-March. A follow-up
mission with two new satellites that will continue the gravity
measurements is currently set for launch this Tuesday from Vandenberg
Air Force Base in California.
Watching The Water Flow
Satellite data accumulated over a 14-year period reveals dramatic changes in the world’s water supply, partly due to natural variation but also because of human activity and climate change
Global Water Storage Trends
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Ivan Semeniuk, John Sopinski And Murat Yükselir/The Globe And Mail
Source: Emerging Trends In Global Freshwater Availability, doi.org
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