This year marks the 100th anniversary of the construction of Elephant Butte Reservoir on the Rio Grande in south-central New Mexico. It was one of the first reservoirs built in the 20th century in an attempt to overcome the critical limitation of water availability on where, when, and how humans could settle the American West. Elephant Butte is the largest reservoir in New Mexico, with the ability to store more than 2.2 million acre-feet of water. An acre-foot is equivalent to 325,851 gallons and is enough to supply water to a family of four for one year. While this reservoir was a marvel in 1916—at the time the largest irrigation reservoir in the world—its utility in the 21st century is now called into question due to rising temperatures and a stark reduction in the Rio Grande’s flows due to human consumption and climate change.
Elephant Butte Reservoir is in the Chihuahuan Desert five miles north of Truth or Consequences, New Mexico. This massive reservoir is approximately four miles wide and 40 miles long. Due to its size and vast surface area, it evaporates 250,000 acre-feet of water per year when it’s full. The evaporation at Elephant Butte far exceeds that of any of the other reservoirs in the Rio Grande Basin and is nearly double that of other high-elevation reservoirs on the Rio Chama in northern New Mexico.
The current evaporation from Elephant Butte Reservoir will only increase as the climate warms. Average annual temperatures in the Basin increased by 2.5 degrees Fahrenheit (ºF) from 1971 to 2012 (0.7ºF per decade). The U.S. Bureau of Reclamation predicts that by the end of the 21st century, temperatures will increase an additional 5ºF to 7ºF, and precipitation will decrease.
Flow declines will result from such rises in temperatures. By 2100, it is predicted that flows in the Rio Grande overall will decrease by at least one-third and could decrease by 50 percent in southern New Mexico and Texas. Such flow changes will have a significant impact on the amount of water available for storage in and evaporation from the reservoirs in the Upper Rio Grande Basin, especially those located at lower elevations, like Caballo and Elephant Butte reservoirs.
Storing water in a low-elevation reservoir like Elephant Butte is extremely inefficient and wasteful and will only become more so, especially given the predicted temperature increases in the Basin. A feasible alternative is to store water upstream in the four high-elevation reservoirs on the Rio Grande and Rio Chama, including Heron, El Vado, Abiquiu, and Cochiti.
Storing Rio Grande Project water in high-altitude reservoirs, even in a dry year like 2013, could save about 40,000 acre-feet of water from evaporating. In an average-rainfall year, like 2010, the savings would be far greater, an estimated 85,000 acre-feet. The conserved water would help offset the impacts of climate change and, if managed wisely, could create significant environmental benefits for the Rio Chama and the 175-mile segment of the Middle Rio Grande between Cochiti Dam and Elephant Butte Reservoir.
Implementing our vision of conserving water in the 21st century by moving reservoir storage upstream and managing our reservoirs in an integrated fashion will require navigating both institutional and legal challenges. Congressional reauthorization will be required in some instances to change how and where water is stored and released. Further, the Rio Grande Compact Commission (representing the three Basin states) will need to approve many of the necessary changes in water storage and management in the Basin.
The looming water scarcity associated with climate change is predicted to sink the Rio Grande Basin into a permanent drought. The solutions of the past century will not serve us in the future. Just as the construction of Elephant Butte Reservoir 100 years ago began a new era of water development, the next 100 years will require us to think equally boldly and to act to overcome the institutional and legal hurdles that currently prevent these necessary solutions from being implemented.
A long-overdue comprehensive evaluation of the reservoirs in the Middle Rio Grande in New Mexico is necessary to bring this idea to fruition. The requested congressional direction and funding mechanisms are already in place in the New Mexico Drought Preparedness Act of 2015, introduced by Senator Tom Udall (D-NM). The concept is sound and with the right backing and implementation could serve as one of the key solutions to ensure water for existing users as well as to ensure environmental flows to protect a living Rio Grande for centuries to come.