A new, U.S.-Mexico agreement provides more Colorado River water to both countries, will require both countries to share inevitable river shortages and offers more certainty as to how much river water will be available for both countries.

That’s how negotiators, federal officials and Arizona water officials see the upshot of the pact that was signed this week at a Santa Fe, New Mexico, ceremony following years of negotiations. The agreement, known as Minute 323, is aimed at establishing ground rules for managing the river for the two countries through 2026. It succeeds an earlier, somewhat less far-reaching agreement, known as Minute 319, that expires this year.

The new agreement also calls for a major cooperative water-saving effort in which the U.S. government and three Lower Colorado River Basin states, including Arizona, agree to invest $31.5 million in lining irrigation canals and improving the efficiency of other agricultural water infrastructure in Mexico.

In return, Mexico will deliver the 220,000-acre-feet of water saved through those conservation measures to Arizona and other Lower Basin states to the Colorado River Delta for environmental restoration and to the river system as a whole to help stabilize the declining Lake Mead.

Besides offering certainty and continued environmental restoration, “Most important, it offers a binational, water scarcity contingency plan,” said Chuck Cullom, Colorado River program manager for the 336-mile-long Central Arizona Project canal system.

The binational plan will kick in when and if Arizona, California and Nevada finally settle on their own plans to reduce water deliveries from the river to stave off future, catastrophic shortages.

Overall, the agreement can be seen as a binational climate adaptation effort, although the phrase “climate change” doesn’t appear in it. It’s aimed at helping preserve river flows and Lake Mead at a time of drought and climate change.

Lake Mead has dropped significantly since it was last full in 1999, and average annual river flows were cut by 19.3 percent from 2000 to 2014, a major study found this year. The river ran strong this year, but authorities have warned this largesse can’t be expected to last forever.

Perhaps even more importantly, many observers say, is that Mexico and the U.S. reached an agreement amid the tension that has dominated their relationship since President Trump took office. He ran on a platform of cracking down on undocumented Mexican immigration and building a border wall costing up to $21 billion.

“Minute 323 is the result of many rounds of technical discussions involving a broad group of stakeholders from both countries. This agreement puts us on a path of cooperation rather than conflict as we work with Mexico to address the Colorado River Basin’s many challenges,” said Edward Drusina, a U.S. commissioner for the International Boundary and Water Commission, in a news release.

While there had been considerable concern that negotiations would suffer, “in my view there have been no changes,” said Tom Buschatzke, director of the Arizona Department of Water Resources.

“I went back to meet with administration officials in Washington in February and explained the importance of Minute 323 to the seven river basin states,” he said. “I came out of that meeting feeling very confident that we had the support of those high-level officials of the Department of the Interior.”

Specifically, the new agreement says:

  • There will be a one-shot allotment of 109,000 acre-feet of river water to the CAP, Southern California’s giant Metropolitan Water District, the Imperial Irrigation District in that state’s Imperial Valley and the Southern Nevada Water Authority. The entities will equally split the water from savings realized by the Mexican conservation projects.
  • Under the drought contingency plans, the Lower Basin states and Mexico will both shave up to 16.7 percent of their river deliveries during shortages, depending on the scale of the shortages.
  • During times of surplus flow — if they occur again — Mexico could take anywhere from 40,000 to 200,000 acre-feet of river water above and beyond the 1.5 million the country is already guaranteed each year under a 1944 treaty. An acre-foot will serve about two homes for a year across the Southwest and more homes in Tucson, whose per-person water use is much lower than the regional average.
  • The two countries will set aside 210,000 acre-feet of water over nine years for environmental restoration work in the Colorado River Delta.

The 27,000 acre-feet that would go to CAP will come after the Mexican conservation projects kick in, CAP’s Cullom said

“When folks in the CAP system need the water, we can release it to them. I don’t know when,” he said. “If the drought contingency plan is implemented, it can be used in normal years or in a shortage year.”

For the much longer term, perhaps the most tantalizing part of the agreement for some water users is a commitment for the countries to set up a group to immediately start preparing for a detailed study of a desalination plant.

The plant could be on the Pacific Coast, along the Gulf of California off the Sonoran coast or near the New River in Baja California.

For the study to begin, money would have to be raised for it.

“I can’t tell you when that study will occur, but we know there is a strong interest in this by the Arizona-Mexico Commission in this work,” said Sally Spener, the U.S. secretary of the international water commission, a binational governmental organization. “That’s why the scope of work is going to be done.”

CAP’s Cullom said he’s optimistic that the study could start as soon as six months from now.

“It’s an opportunity to increase water supply to benefit both countries. We recognize it will take a very long time to develop, but the time to start that work is now,” Cullom said.

But all parties to the agreement are also aware that the plant, besides offering new water for existing and future users, will likely be controversial due to a high cost, significant energy use and potential environmental impacts.

Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. On Twitter@tonydavis987