(CN) — With Arizona farmers expecting to take hit next year on their allocation of Colorado River water, water planners, managers, and researchers statewide are keeping a close eye on models that show the shortage could hit cities and towns in the next few years.
Arizona would lose 512,000 acre-feet under a Bureau of Reclamation Tier 1 shortage expected next month, but the reduction would not affect average Arizonans, said Thomas Buschatzke, director of the Arizona Department of Water Resources.
“No municipal providers, no one in their house, is going to lose any of their water,” Buschatzke said. “It’s really agriculture that’s taking a hit.”
If Lake Mead’s surface dips below 1,075 feet elevation, Reclamation will declare a Tier 1 shortage and Arizona will lose about a fifth of its 2.8 million allocation, Buschatzke said.
One acre feet is 326,000 gallons, enough water for about 3.5 average households, according to ADWR.
Planning for this day started almost a century ago.
In 1922, Arizona, California, Colorado, New Mexico, Nevada, Utah and Wyoming agreed to share what they thought would be 15 million acre-feet of water per year. A dividing line at Lee’s Ferry, Arizona split the states into upper and lower basins. Arizona, which except a small portion near Lee’s Ferry, falls in the lower basin with California, and Nevada.
In 1928, Congress authorized Boulder (now Hoover Dam) near Las Vegas to store water for the lower basin. That law also gave California 4.4 million acre-feet of water, Arizona received 2.8 million, and Nevada received 300,000 acre-feet, the current allocation. Later, Glen Canyon Dam in Marble Canyon created Lake Powell in Utah.
In Arizona, about half of the river water is pumped uphill from Lake Havasu through Phoenix to Tucson in a 336-mile canal started in 1973 and completed in 1993. The Central Arizona Project, launched by President Lyndon Johnson in 1968 and completed under President Bill Clinton, supplies farms and cities along the state’s central population centers.
The system includes 14 pumping stations and six recharge sites, where the water is allowed to trickle down into the aquifer. Lake Pleasant, a boating Mecca north of Phoenix that is filled with CAP water, serves as an emergency backup for the Phoenix metropolitan area.
In June, Bret Esslin, an ADWR Colorado River engineer, told Pinal County groundwater users, mainly agricultural users, that even if inflow to the Colorado system is 100% of normal for the rest of the year — a highly unlikely scenario — the river’s water intake will only be 73% of normal.
The lakes on the river, where the Bureau of Reclamation dams retain the water for later use, were at a combined 41% of normal in June. Last summer, they were at 50%. Lake Mead, the largest reservoir in the nation, was 37% full by June. Lake Powell was just 34% full, Esslin said.
Also in June the Arizona Department of Water Resources Post-2025 committee looked at long-term solutions to the drought and potential for worse days ahead. Current models show that demand will start to outstrip supply sometime in the 2030s, according to ADWR chief hydrologist Jeff Inwood.
Most of that unmet demand will be in central Arizona’s Pinal County, where large scale farmers grow cotton, alfalfa, corn and other crops.
Although half of Arizona’s water comes from the Colorado River, the other half comes from surface water, largely runoff from the Salt and Verde rivers, or groundwater pumping. Groundwater pumping is a touchy subject in Arizona, where agricultural users have pumped so much groundwater that the ground sank by more than 20 feet in some places in Pinal County between Phoenix and Tucson.
Now farmers offset groundwater pumping by using CAP water, but if the Colorado River shortage continues and they pump more groundwater, that will run short too, Inwood said.
Until 2019, Arizona had “excess” Colorado River water. That water, much of which goes to municipal customers of the CAP, is banked underground. The state’s Water Banking Authority, an arm of ADWR, manages storage for water users. Buschatzke chairs the commission that leads the authority.
The state has stored more than 4 million acre-feet of water. Those water “credits” likely won’t be tapped until a Tier 3 shortage, Buschatzke said.
Cities, towns and tribes won’t lose any of their CAP allocations for several years, but the state’s largest city, Phoenix, has been planning for such times for more than a century, said the city’s water resource management advisor Cynthia Campbell.
“We live in a hot, dry climate. It was a hot dry climate before climate change, and it may be a hotter, drier climate after climate change,” Campbell said. “For over 100 years the city of Phoenix has been in an environment that is sometimes subject to drought and is always subject to water scarcity.”
The city evolved to use an array of water sources — the Colorado River (40%), the Salt and Verde rivers (60%) and groundwater (about 1%) make up the lion’s share. A robust water reclamation operations adds to the bucket, and Phoenix has banked water in aquifers for years, Campbell said.
“We have enough water banked to supply all of our customers that are using Colorado River water for at least a year,” she said.
Water in the Salt and Verde rivers is not as depleted as the Colorado. Last year, the main storage on the system, Roosevelt Lake, was 100% full, and now it’s at 70% capacity, Campbell said.
Sharon Megdal, director of the University of Arizona Water Resources Research Center, has been studying the Colorado River system since the early 1990s. At that time, the biggest worry in Arizona was using all of the water. Any unused water would run downstream where California can claim it, Megdal said.
Banked water will continue to increase for now, but could be tapped soonto make up for further shortages, she said.
“Come 2024, we could be looking at a Tier 3,” Megdal said. “That affects cities. That affects the tribal priority water, and that’s where the Water Banking Authority comes in to mitigate.”
Megdal thinks Arizonans will evolve with their environment. Communities will put existing drought plans into effect, people will make personal choices that save water and agriculture will change. She cites the Salt River Project, which supplies Phoenix, as an example.
Originally 90% of that water went to agriculture; now just 10% does, Megdal said.
“I think we’ll adapt. I don’t think we’ll run out of water,” she said.
Ultimately it’s the residents who use the water from the Colorado River, and they don’t just drink it.
John Keegan, 49, lives in Flagstaff about two hours away from the Colorado. He makes his living from a short-term rental in the mountain city, and he considers the river a treasure.
“I try kayak and camp on the Colorado a few times a year,” Keegan said. “It’s the perfect way to escape. Time stands still, stress melts off your back, and nature’s art takes over. It’s a perfect way to refresh, and I’m lucky that it is literally in my backyard.”
The Bureau of Reclamation is expected to announce the Tier 1 shortage Aug. 16.
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