A new satellite study finds more than 75% 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.
|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. Credit: U.S. Bureau of Reclamation. Click to enlarge.|
This study is the first to quantify the amount that groundwater contributes to the water needs of western states. According to the US 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 study has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
The research team, led by NASA and University of California, Irvine, scientists, 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.
We don’t know exactly how much groundwater we have left, so we don’t know when we’re going to run out. This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking.—Stephanie Castle, lead author
Water above ground in the basin’s rivers and lakes is managed by the US 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. There’s just not enough information available from well data to put together a consistent, basin-wide picture.—senior author Jay Famiglietti
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.
Famiglietti noted that the rapid water 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.—Jay Famiglietti
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.
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.
Stephanie L. Castle, Brian F. Thomas, John T. Reager, Matthew Rodell, Sean C. Swenson and James S. Famiglietti (2014) “Groundwater Depletion During Drought Threatens Future Water Security of the Colorado River Basin,” GRL doi: 10.1002/2014GL061055