New Mexico, already being sued by Texas over Rio Grande water, will have an increasingly difficult time in coming decades meeting its legal obligation to deliver water to its downstream neighbors, according to a new federal study.
Higher temperatures are bringing a double whammy, reducing water supplies through evaporation from reservoirs and rivers while increasing water consumption by gardens, farms and the Rio Grande’s riverside forests, according to a new analysis by the U.S. Bureau of Reclamation and Sandia National Laboratories.
“The supplies are going down, and the demands are going up,” said Sandia’s Jesse Roach, one of the study’s authors.
Scientists have repeatedly projected decreased river flows in the region as a result of rising temperatures, which are driven by increasing greenhouse gases. The new study is the most detailed effort to date to tease out the water policy implications.
The scientists found that if New Mexico water use patterns are not changed, the state will run an increasing deficit in its legal obligation under the Rio Grande Compact to deliver water to Texas. The study comes as Texas is in court, asking the U.S. Supreme Court to take up a dispute over whether current New Mexico water practices are illegally depleting the Rio Grande’s flow before it reaches the New Mexico-Texas state line.
The study, lead by Dagmar Llewellyn at the Bureau of Reclamation’s Albuquerque office, is part of the agency’s West Wide Climate Risk Assessment, an effort to determine water supply risks basin-by-basin across the western United States. The full study is scheduled for release later this summer, but Llewellyn and Roach have begun presenting their results at scientific conferences, including a meeting of the American Geophysical Union last month in Washington, D.C.
Llewellyn will make the first major public presentation on the team’s research this evening in a talk at the New Mexico Museum of Natural History and Science in Albuquerque.
The goal of the study, Llewellyn said in an interview this week, is to provide data needed to foster a community conversation among New Mexicans about allocation of the state’s increasingly scarce water. “A lot of it’s going to be just figuring out our priorities,” she said.
The study plugs data from climate simulations into “URGSiM,” Sandia’s Upper Rio Grande Simulation Model, to determine how changes in river flows would affect the dams and diversions used by the valley’s farms and cities. The only way to meet water needs as river flows decline, the study found, is to shortchange deliveries of water to Elephant Butte Reservoir. But those deliveries are mandated by law to provide a share of the water to farmers and cities in southern New Mexico, Texas and Mexico.
Llewellyn and Roach also concluded that supplies of water imported for use in Santa Fe and Albuquerque via the San Juan-Chama project are vulnerable to more frequent shortages as a result of climate change.
In interviews and their scientific presentations, Llewellyn and Roach cautioned that their findings include significant uncertainties.
The core finding, however – less water in New Mexico in the future as a result of rising temperatures – remains consistent across a range of different assumptions.