The Colorado River Basin lost nearly 53 million
acre feet of freshwater over the past nine years, according to a new study based
on data from NASA’s GRACE mission. This is almost double the volume of the
nation's largest reservoir, Nevada's Lake Mead (pictured).
Image Credit:
U.S. Bureau of Reclamation
A new study by NASA and University of California, Irvine, scientists finds
more than 75 percent of the water loss in the drought-stricken Colorado River
Basin since late 2004 came from underground resources. The extent of groundwater
loss may pose a greater threat to the water supply of the western United States
than previously thought.
This study is the first to quantify the amount that groundwater contributes
to the water needs of western states. According to the U.S. Bureau of
Reclamation, the federal water management agency, the basin has been suffering
from prolonged, severe drought since 2000 and has experienced the driest 14-year
period in the last hundred years.
The research team used data from NASA's Gravity Recovery and Climate
Experiment (GRACE) satellite mission to track changes in the mass of the
Colorado River Basin, which are related to changes in water amount on and below
the surface. Monthly measurements of the change in water mass from December 2004
to November 2013 revealed the basin lost nearly 53 million acre feet (65 cubic
kilometers) of freshwater, almost double the volume of the nation's largest
reservoir, Nevada's Lake Mead. More than three-quarters of the total -- about 41
million acre feet (50 cubic kilometers) -- was from groundwater.
The Colorado River Basin (black outline) supplies
water to about 40 million people in seven states. Major cities outside the basin
(red shading) also use water from the Colorado River.
Image Credit:
U.S. Bureau of Reclamation
"We don't know exactly how much groundwater we have left, so we don't know
when we're going to run out," said Stephanie Castle, a water resources
specialist at the University of California, Irvine, and the study's lead author.
"This is a lot of water to lose. We thought that the picture could be pretty
bad, but this was shocking."
Water above ground in the basin's rivers and lakes is managed by the U.S.
Bureau of Reclamation, and its losses are documented. Pumping from underground
aquifers is regulated by individual states and is often not well documented.
"There's only one way to put together a very large-area study like this, and
that is with satellites," said senior author Jay Famiglietti, senior water
cycle scientist at JPL on leave from UC Irvine, where he is an Earth system
science professor. "There's just not enough information available from well data
to put together a consistent, basin-wide picture."
Famiglietti said GRACE is like having a giant scale in the sky. Within a
given region, the change in mass due to rising or falling water reserves
influences the strength of the local gravitational attraction. By periodically
measuring gravity regionally, GRACE reveals how much a region's water storage
changes over time.
The Colorado River is the only major river in the southwestern United States.
Its basin supplies water to about 40 million people in seven states, as well as
irrigating roughly four million acres of farmland.
"The Colorado River Basin is the water lifeline of the western United
States," said Famiglietti. "With Lake Mead at its lowest level ever, we wanted
to explore whether the basin, like most other regions around the world, was
relying on groundwater to make up for the limited surface-water supply. We found
a surprisingly high and long-term reliance on groundwater to bridge the gap
between supply and demand."
Famiglietti noted that the rapid depletion rate will compound the problem of
short supply by leading to further declines in streamflow in the Colorado
River.
"Combined with declining snowpack and population growth, this will likely
threaten the long-term ability of the basin to meet its water allocation
commitments to the seven basin states and to Mexico," Famiglietti said.
The study has been accepted for publication in the journal Geophysical
Research Letters, which posted the manuscript online Thursday. Coauthors
included other scientists from NASA's Goddard Space Flight Center, Greenbelt,
Maryland, and the National Center for Atmospheric Research, Boulder, Colorado.
The research was funded by NASA and the University of California.
For more information on NASA's GRACE satellite mission, see:
and
GRACE is a joint mission with the German Aerospace Center and the German
Research Center for Geosciences, in partnership with the University of Texas at
Austin. JPL developed the GRACE spacecraft and manages the mission for NASA's
Science Mission Directorate, Washington.
NASA monitors Earth's vital signs from land, air and space with a fleet of
satellites and ambitious airborne and ground-based observation campaigns. NASA
develops new ways to observe and study Earth's interconnected natural systems
with long-term data records and computer analysis tools to better see how our
planet is changing. The agency shares this unique knowledge with the global
community and works with institutions in the United States and around the world
that contribute to understanding and protecting our home planet.
To learn more about NASA's Earth science activities in 2014, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
[PDF 67KB]
