The Colorado River Basin supplies water to 40 million people in seven states (Arizona, Colorado, Utah, Wyoming, California, New Mexico and Nevada) and irrigates approximately 4 million acres of farmland.
The new study on the region, published in the journal Geophysical Research Letters and conducted by scientists from NASA and the University of California, Irvine, used data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission. Prior to the GRACE data, only surface water loss in the area was well documented. From 2004-2013, the satellite measured the gravitational pull of the Basin as it rose and fell over time, denoting changes in the subterranean water reserves.
The scientists determined that, since 2004, over 75 percent of the water loss in the region was from groundwater (underwater resources). Moreover, the total amount of water loss is nearly double the volume of the nation’s largest reservoir, Lake Mead, which last week reached its lowest water level in its history.
“This is a lot of water to lose,” says the study’s lead author Stephanie Castle, a water resources specialist at the University of California, Irvine. “We thought that the picture could be pretty bad, but this was shocking.”
“We don’t know exactly how much groundwater we have left,” she added, “so we don’t know when we’re going to run out.”
According to the U.S. Bureau of Reclamation, the entire Colorado Basin has suffered severe drought since the year 2000. The largest state, California, is in the midst of a three-year drought that is estimated to cost its economy $2.2 billion in 2014 and may require mandatory water restrictions.