Jason Tucker’s job title is facility manager at the Glen Canyon Dam. But you could also say he’s also a kind of banker.

Colorado River water flows into his bank – the reservoir behind the dam. He can then loan it out to create electricity. Some even call the dam here a kind of “savings account,” tapped as needed to replenish Lake Mead and the Hoover Dam, which lie past the Grand Canyon to the west.

But the currency here is, of course, water – a lifeblood of any community and particularly precious here in the arid American West. Mr. Tucker marvels when ponders the role that this one river plays.

“When I look at this itty bitty strip of water and the fact that it is supporting life in the Southwest for tens of millions of people – that little span right there is all the water for the southern Southwest. It just blows my mind,” Tucker says while standing on a bridge above Glen Canyon Dam, nestled into the red rock holding back Lake Powell and all its tourist-filled house boats.

Now, though, the analogy of Lake Powell as Lake Mead’s safety net has been coming under increasing doubt. Last year, the agency that oversees federal dams was projecting a near 50-50 chance that in 2018 Lake Mead would for the first time fail to deliver enough water to the states that depend on it.

Snows and rainfall this winter have eased that worry, but the long-term threat of water shortages is real, as climate change and population growth create new pressures on supplies. Stakeholders here are responding, with potential answers that range from better management of dams to new conservation efforts.

One contentious proposal is to tear down Glen Canyon Dam, allowing the river to flow straight to Lake Mead. In all likelihood, though, states that rely on the river will continue a recent pattern of negotiation that contradicts the basin’s reputation for “water wars.”

Negotiators are aiming to reach two separate deals across seven states and Mexico, and the agreements could encourage water users to proactively curtail how much they pull from the river in order to stave off more drastic, automatic shortages in the future.

“It’s often referred to as the most litigated river in the world. That might have been true in the 1960s, but I think in the last 20 years it’s become a model for compromise and shared-sacrifice among the states,” says John Entsminger, general manager of the Southern Nevada Water Authority. “The real question is what’s the next iteration of that cooperative partnership?”

Climate forecast

Climate change is drawing that question into sharper focus. Scientists’ models predict a drier, more drought-prone Southwest. And warmer temperatures promise to increase evaporation rates at reservoirs, further challenging the dams.

Jacob Turcotte/staff The Colorado River Basin spans much of the American Southwest – and the river represents a vital water supply for the region. Stories in this series of articles were reported in cities highlighted on this map, as well as in Scottsdale, Ariz., which is in the greater Phoenix area.

Already, conditions at these huge lakes have changing. Lake Mead hit a record low in 2015, and outflows have exceeded inflows by more than 9.2 million acre-feet, or nearly 3 trillion gallons of water. Much like the previous two years, Lake Powell began 2017 near the 2005 record low of about 50 percent capacity, though the snowy winter indicate water levels could top two-thirds of storage capacity by 2018.

Here’s where things can get tricky.

If Lake Mead were to fall for the first time ever below 1,075 feet elevation from sea level, that would trigger a delivery shortage that largely hits Arizona. The region barely avoided a shortage in 2016, as Lake Mead sat just shy of 1,081 feet.

Though far off, a “deadpool” scenario looms that would threaten hydropower production. If Lake Mead falls below 895 feet, Hoover Dam turbines would suck in air, rendering them inoperable.

“Continuing to conserve water is not going to be enough. Perhaps sooner or later you’ll actually have to take the shortages outlined,” predicts Tom Buschatzke, director of the Arizona Department of Water Resources. “Hope for rain and snow is not a plan.”

At the bargaining table

The three lower basin states – California, Arizona and Nevada – have begun to address the issue.

In a deal that's been under negotiation for some time, and with talks still under way, the states would voluntarily reduce the water they take from the Colorado River to avoid more severe reductions later. They want to save 1.2 million acre feet, a big deal for states that have a total allocation of 7.5 million acre feet per year.

Zack Colman/The Christian Science Monitor View from the top of Glen Canyon Dam near Page, Ariz. The Glen Canyon Dam and its reservoir, Lake Powell, act as a sort of savings account in times of scarce water resources for Lake Mead, further west on the Colorado River.

Arizona, and especially its farmers, could face the steepest water cuts. In a 1968 deal for water, the state agreed to a “junior” rights, meaning every other state must get their water before Arizona can get a drop. The state is agreeing to curb consumption from the Colorado River by at least 7 percent, if Lake Mead is below 1,090 feet elevation. The cuts would jump to nearly 25 percent in a worst-case scenario in which Lake Mead drops 45 feet or more below that.

Nevada would take a 10-percent reduction in a worst-case scenario.

Perhaps the biggest potential concession would involve California forgoing some of its Colorado River water for the first time. The state has senior rights, meaning it gets all of its water first. A proposal by state representatives, would leave 4.5 percent to as much as 8 percent of the state’s 4.4 million acre-feet of water in Lake Mead, if trigger levels of 1,045 feet or 1,030 feet are breached.

“If everyone is intransigent and does nothing, then we all lose,” says Jeffrey Kightlinger, general manager with the Metropolitan Water District of Southern California, a big water user that serves the Los Angeles area.

The incentive to cooperate

Each state has reasons to deal because the federal government can order cuts in the event of a shortage, making supplies uncertain. Congress also could butt in, which is a tantalizing proposition for some Western lawmakers – especially non-California ones – who might seek a greater slice for their states than today’s 95-year-old water-sharing pact affords.

“The lower basin states wanted to control their own destiny rather than have to take an order from the secretary of the Interior or a judge,” says Mr. Buschatzke in Arizona.

But even beyond the negotiations, federal and state actors are are trying to extend the life and water supplies of Lake Powell and Lake Mead.

The federal Bureau of Reclamation, which manages the two big dams, is funding retrofits that would make turbines more efficient in low-water conditions. The enormous waterwheels at Glen Canyon Dam have been rusting, the corroded stainless carbon steel blades creating a drag as water flowed through them to spin the turbines. Tucker says the eight new turbines will improve hydropower efficiency enough to pay off the $400 million upgrade in eight years.

“As you know, we’re limited by how much comes in. But how we manage it and use it – that can change,” Tucker says.

At Lake Mead, meanwhile, the Southern Nevada Water Authority was worried enough about the water levels that it paid $817 million to install a third intake at lake-bottom, to help safeguard water customers from the risk of falling lake levels. The intake, funded by a 9-percent rate increase for customers over three years, was finished in late 2015.

Tear down a big dam?

But despite all the bargaining and investments, some observers argue that conditions are changing too drastically to sustain both big lakes.

“Fill Mead First” is the slogan of those who want to remove a dam and let Lake Powell flow directly into Lake Mead. The plan’s proponents, led by the Glen Canyon Institute, contend climate change means that Lakes Powell and Mead are unlikely to ever refill.

On top of that, they say a significant amount of water escapes Lake Powell through porous sandstone. They contend combining Lake Powell and Lake Mead would reduce water loss due to evaporation.

The proposal is contested by state and federal water officials, among others.

“I think it is scientifically dubious, legally implausible and politically suicidal,” says Mr. Entsminger in Nevada.

While federal dam operators don’t deny there’s a structural imbalance for Southwestern water, they question some of the science behind “Fill Mead First.” They say water lost through Lake Powell leakage hasn’t been proven and that evaporation would increase if all the water was stored in Lake Mead, which is in a hotter climate. On top of that, Lake Powell holds back sediment that would considerably reduce storage capacity in Lake Mead if its northeastern neighbor didn’t exist.

The drive for efficiency

If authorities are opposed to “Fill Mead First,” they can’t afford to sit on their hands. The realities on the river are changing faster than they ever believed possible. That’s largely due to climate change.

“The situation is more dynamic and moves faster,” says Mr. Kightlinger in Southern California. “Here we are essentially a decade later trying to update those shortage guidelines,” reached in 2007.

“We’ll probably be in a world where we have to update this every decade,” Kightlinger says. He quickly reevaluates. “I think we’ll be lucky if we only have to do it once a decade.”

For him and others, there’s hope in the imperatives of continued negotiation and a drive for efficiency. Already cities like Los Angeles are using less water than had been predicted a generation ago.

It might sound like a risky strategy to hope that conservation and efficiency outpace the reduction in water supplies, but Buschatzke in Arizona says there’s more coordination on the Colorado River than people realize.’

“I can think of a bunch of radical ideas that are not in the realm of the possible,” he says. “If we can do these incremental additions and achieve the same goals with a lot less pain, we’re going to do that.”

Reporting for this story was supported by a fellowship at the Bill Lane Center for the American West, at Stanford University.

This is the sixth and final article in a series on solving water challenges in the American West.

Part 1: West's challenge is still water scarcity, wet winter or not

Part 2: In arid Southwest, cities expand but use less water

Part 3: America's biggest water users – farmers – learn to use less of it

Part 4: How water swaps help the West manage a precious resource

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Part 5: Why solar panels bloom in Southwest's land of hydropower

Part 6: For water users on Colorado River, a mind-set of shared sacrifice