Drought, combined with well pumping in the past decade, has drained Colorado River Basin groundwater at an alarming rate, according to a new study by NASA and University of California, Irvine scientists.
The implications could be severe for 40 million people in the seven states that depend on Colorado River Basin water, including New Mexico.
“The take-home message is we have depleted a lot of groundwater already,” said Stephanie Castle, a water resources specialist at the University of California, Irvine, and the study’s lead author. “We aren’t managing groundwater as carefully as our reservoirs, and it is our strategic supply during times of drought. We really don’t know how much we have or how much we are using.
“It would be really scary if groundwater dried up and we didn’t have that as a backup during drought,” Castle said during an interview Thursday.
Still, New Mexico’s share of Colorado River Basin water isn’t likely to be affected by groundwater depletion in the short term, said Kevin Flanigan, Colorado River Bureau chief for New Mexico’s Interstate Stream Commission. The groundwater depletion primarily affects the lower Colorado River Basin states of California, Nevada and Arizona, he said.
New Mexico’s share of the Colorado River Basin is largely from the San Juan-Chama Project, which brings water from the San Juan River through a tunnel to New Mexico. The San Juan-Chama Project water is a major supply source now for Santa Fe and Albuquerque.
In addition, there is little groundwater use in the New Mexico portion of the Colorado River Basin. “In the San Juan, there’s not that much of a groundwater resource to go after,” Flanigan said.
Water managers see groundwater as a resource bank that can supply water as streamflows and lakes dwindle under withering drought. But the recent study, accepted for publication in the journal Geophysical Research Letters, found the basin had lost 41 million acre-feet of groundwater between 2004 and November 2013, accounting for the majority of all water depleted in the region. The total water depleted equals almost two Lake Meads.
“This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking,” Castle said in a statement.
Water levels at Nevada’s Lake Mead, the largest reservoir in the nation, and Lake Powell, the primary storage sites for the Colorado River, have been declining steadily. The study found groundwater was being depleted at a rate much greater than the reservoirs. “It’s disappearance may threaten the long-term ability to meet future allocations to the seven Basin states,” the study says.
“The Colorado River Basin is the water lifeline of the Western United States,” said Jay Famiglietti, who worked on the study and is a senior water cycle scientist at the Jet Propulsion Laboratory while on leave from UC-Irvine.
“With Lake Mead at its lowest level ever,” he said, “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.”
Groundwater stored in the West’s aquifers are primarily recharged through snowmelt. The decline in snowpack in the last several years means groundwater isn’t restored as it is pumped out by utilities, cities and farmers. The Colorado River Basin groundwater tapped by thousands of wells has been there for centuries or millennia and isn’t easily replaced.
The Colorado River Basin water was divided up between seven Western states through a compact negotiated in 1922 at Bishop’s Lodge in Santa Fe. The compact split the basin into upper states and lower states. The lower basin states of California, Arizona and Nevada use more water than the upper states, which include New Mexico.
Between all the users, the Colorado River Basin streamflows are now “the most over-allocated in the world,” the study says.
The study, “Groundwater Depletion During Drought Threatens Future Water Security of the Colorado River Basin,” was released Thursday. It is based on a new technology using two satellites to measure the loss of water mass from above and below ground in the Colorado River Basin. As water mass shrinks or grows, the gravitational pull on the satellites is altered, a change scientists can measure.
The two satellites, part of NASA’s Gravity Recovery and Climate Experiment, travel one behind the other in orbit, reacting to the water in snowpack, reservoir levels and groundwater.
“We can isolate changes in groundwater,” Castle said. “The two [satellites] are looking at each other and not at the Earth. The distance between the two satellites and the dance that they do is what we measure.”
Researchers from UC-Irvine, the NASA Jet Propulsion Laboratory, the NASA Goddard Space Flight Center and the National Center for Atmospheric Research collaborated on the study.
Castle said the Rio Grande Basin through the heart of New Mexico is large enough to be a candidate for a similar groundwater study. “I would be interested in doing it if there’s a need,” she said.
Contact Staci Matlock at 986-3055 or email@example.com. Follow her on Twitter @stacimatlock.