In this Aug. 13, 2020, file photo a bathtub ring of light minerals delineates the high water mark on Lake Mead at the Lake Mead National Recreation Area, near Boulder City, Nev. (AP Photo/John Locher, File)

Arizona may be facing its first official declaration of water shortage next year, a move that would trigger water cutbacks of 512,000 acre-feet — almost 20% of Arizona’s Colorado River entitlement — affecting mainly agricultural users.

The 24-Month Study on the Colorado River system, released this month by the Bureau of Reclamation, projects that in June water levels in Lake Mead will fall below 1,075 feet for the first time, which would put the state in a Tier 1 shortage.

A Tier 1 shortage, which is highly likely for 2022 and 2023, would mean a reduction of about 30% of the Central Arizona Project’s delivery supply, but the shortage wouldn’t be declared until officials see the August 24-Month Study, which they use to make water allocation decisions.

The state is currently operating in Tier 0, where CAP takes a 192,000 acre-foot reduction to its water supply. One acre-foot, enough water to cover an acre a foot deep, provides three Phoenix area households with water a year.

Most of the burden for the potential cutbacks would fall on CAP and agricultural water users in central Arizona due to CAP’s “junior” status among states using the Lower Basin and CAP’s priority system, which protects water used by municipal, industrial and tribal users.

Arizonans shouldn’t panic though, water officials say. The cutbacks wouldn’t take away from water supply to high-priority parties like cities and tribes. Experts have repeatedly emphasized that the report, while significant, is not a surprise.

“Generations of Arizonans have anticipated a day of shortage and planned accordingly. We should be immensely proud of the foresight of literally generations of Arizona leaders,” CAP board member Terry Goddard said at the Arizona Capitol Times Morning Scoop April 20. “Arizona is prepared, Arizona water managers have long understood the risks, and had been planning for them for decades.”

According to CAP Colorado River Program Manager Chuck Cullom, about 70% of Arizona’s Colorado River supply goes to agriculture. In a normal year, CAP delivers about 1.6 million acre-feet of water to urban, tribal and agricultural users in Maricopa, Pinal and Pima counties, where 80% of Arizona’s population resides.

Other deliveries go to users along the Colorado River from Yuma to Mohave County. More than 90% of water supply to on-river users goes to agriculture, but because on-river agriculture has senior priority within CAP, it will not be impacted by a Tier 1 shortage.

“The agricultural users in Pinal County, the non-tribal users are going to suffer this significant reduction, they’re going to lose two–thirds of their water supply,” Cullom said. “In contrast, the lettuce growers in Yuma will have a full supply. So central Arizona agriculture, because of their priority, is heavily impacted by Colorado River shortages, whereas the on-river communities are not.”

Water flows through this canal Saturday, June 27, 2020, in Laveen, Ariz. Central Arizona has been booming — more people, more houses, more need for water. There’s also a long-term drought, and less water to buy from the Central Arizona Project canal system. (AP Photo/Ross D. Franklin)

This will call for collaboration between urban and agricultural communities to mitigate the impact of those shortages on central Arizona agriculture.

Cullom said agricultural users have been working for many years to develop their groundwater capacities in preparation for reductions. In 2022, many central Arizona cities will share a portion of their surface water supply with central Arizona agriculture so they have at least one-third of their original supply, he said.

“I don’t think it’s been done before, it’s pretty unique, and it was developed to soften the impact of this abrupt reduction in supply to agriculture in central Arizona,” Cullom said.

According to Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, three main reasons have contributed to the anticipated cuts in water supply: over two decades of drought in the Colorado watershed; over–allocation of available water; and what climate experts and hydrologists think is a long-term aridification of the system.

“Running out of water is not on the table. I mean, we don’t think that snow is not going to fall in the Rockies,” she said. There is still a lot of give in the system, and water can be allocated from other areas that aren’t experiencing shortages, she said. “Surface water tends to be renewed. It’s just we may permanently have less available.”

Porter said the initial planning for water allocation in the Colorado River Lower Basin, which dates to the creation of the upper and lower basins in 1922, is part of the reason why the state faces an increasing “structural deficit” — when more water is allocated to users than is available in an average year.

In that planning process, evaporation and system losses, which occur as water is moved place to place, weren’t factored into how much water would be available for use, Porter said.

For many years, people didn’t worry about the failure to account for evaporation and system losses because users didn’t take all the water allocated to them, Porter said, but that has changed over time.

“If when all those allocations were made, the people doing the allocating … had built in evaporation and system losses, we would have different allocations. Less water allocated, but we wouldn’t have this built-in problem of a declining Lake Mead,” she said.

Future measures to further mitigate shortage include more local conservation efforts, widening a dam to reduce water spillage, treating wastewater to make it potable, desalination, enhancing current water reclamation projects and direct customer outreach to help teach water efficiency, water managers said.

Cullom said Arizona water managers have long understood the risk to the Colorado River supply and have taken proactive measures that have been largely successful.

“We have been storing water underground in our water banking programs, we have been storing water in Lake Mead, as a means to provide a resource when we have to suffer these reductions,” Cullom said. “So, the fact that there’s a reduction is an expected outcome, and there’s still a significant amount of Colorado River coming to Arizona, and it will serve on-river agriculture and central Arizona cities and tribes for many years to come.”