From The Economist:

The effects of climate change are being exacerbated by a century of bad policy

There are two main reasons water shortages loom. The first is climate change. Both reservoirs straddle the Colorado River as it meanders from its headwaters in the Rocky Mountains down through the desert south-west to northern Mexico (see map). Warmer winters caused by rising greenhouse-gas emissions have diminished the snowpack that melts into the river each spring. In addition, parched soils have soaked up some of the runoff before it can reach Mead and Powell. Since 2000, when the so-called “Millennium Drought” began, the river’s annual flow has shrunk by nearly 20%. Multiple studies in the past five years have attributed up to half of that decline to human-caused climate change.

Second, poor policy choices 100 years ago all but guaranteed that the water available to westerners could never meet expectations. After laws such as the Homestead Act encouraged white settlers to move West in the second half of the 19th century, the federal government financed the dams and pipelines needed for cities and agriculture to thrive in the desert. “By moving water around from more water-rich areas to water-poor areas, we sort of enabled these people to migrate and settle,” says Newsha Ajami of Stanford University. “Regardless of the fact that it’s dry, or it’s hot—if the water is flowing, you think anything is possible.”

Boosterism for shiny new reclamation projects in the early 1900s led to dubious decision-making. The Colorado River Compact, which divvied up the river in 1922, used data from historically wet years to estimate the average annual flows. John Fleck, the director of water resources at the University of New Mexico, says a government scientist was ignored when he testified in the 1920s that the river could not meet its projected demands. The compact and its addendums, known as “the law of the river”, hold that the seven states and Mexico are to split 20.4bn cubic metres of water each year (or in American terms 16.5 million acre-foot of water, where an acre-foot is the amount of water it would take to submerge one acre of land one foot deep.) The river has not lived up to those aspirational figures, says Brad Udall, a climate scientist at Colorado State University. Between 1906 and 1999 annual flows averaged 15.2m acre-feet; since 2000 the river has mustered only 12.4m.

Drought almost seems too puny a word to describe the water scarcity that the south-west is experiencing. “In some ways drought implies that it’s ephemeral,” says Kristen Averyt, Nevada’s climate policy coordinator. But the region’s future could be hotter and drier still, according to the most recent report from the Intergovernmental Panel on Climate Change. When discussing the outlook for Las Vegas, John Entsminger, who runs the Southern Nevada Water Authority (SNWA), prefers to talk in terms of aridification, or the long-term drying of the region. “I’m past talking about droughts,” he says.

The region’s rich cities have been planning for this. Los Angeles, San Diego, Phoenix and Las Vegas all get water from the Colorado River—and all have diversified their water supplies. Investing in conservation, recycling programmes and desalination technology has allowed south-western metros to save water even while their populations have soared.

Perhaps no place is more spooked by Lake Mead’s decline than the Las Vegas valley, which gets 90% of its water from the nearby reservoir. That dependence has spurred innovation. All water that goes down a drain is recycled, according to SNWA, and the city has ripped out grass in favour of desert landscaping. These measures, along with water restrictions and incentives, helped the valley cut its water use by 23% since 2002 while adding about 800,000 residents to its population. “People always assume that population growth and water consumption is more or less a one-to-one correlation,” says Mr Entsminger. But “you can add more people to the equation and simultaneously use less water.”

But cities only account for a fraction of water use on the Colorado. Irrigated agriculture slurps up about 70% of the river each year. Cuts to the water supply may push farmers to grow different crops, fallow fields or return to pumping groundwater to get by. Pumping isn’t a sustainable option either. Years of overuse have depleted aquifers in parts of Arizona and California.

Meanwhile, some demands on the river are growing. Thanks to generations of neglect, many Native American households do not have access to clean drinking water. Tribes also lack the plumbing needed to take the water they already have rights to. The bipartisan infrastructure bill that passed the Senate last week includes $6bn to help remedy that. As the river shrinks, will such attempts to right enduring wrongs go down the drain?

From AZCentral.com (Joanna Allhands):

Opinion: A Tier 1 water shortage on Lake Mead might sound scary, but it’s not the problem we should be worrying about.

There’s a lot of freaking out about the first Tier 1 water shortage at Lake Mead, which is expected to be announced on Aug. 16.

There has been breathless coverage for weeks in the national press about how bad things are now for those of us who rely on the Colorado River.

But that’s the thing. A Tier 1 shortage is far from a crisis.

Oh, this level of shortage will be painful, especially for farmers in Pinal County who are losing their only source of renewable water. They have no option other than to turn back to groundwater, which already has dwindled to the point that it cannot meet the long-term demands of all Pinal users. Some farmers are already beginning to make tough choices about which fields to fallow and which of their most productive lands are worth saving.

But cities in metro Phoenix will not yet feel any ill effects of a Tier 1 shortage (and few will notice the impacts of a deeper Tier 2 shortage, a growing possibility for 2023). And those with the highest priority on-river water are even more insulated from pain, even if things get worse than that.

A Tier 1 shortage isn’t our problem now

Arizona has known for years that this day would come. We planned for it in a statewide implementation plan, which provides a complex web of temporary water supplies and compensation to help those who must shoulder these cuts. The plan gets progressively more painful, especially once we hit a Tier 3 shortage that will impact even the largest cities in metro Phoenix, but it’s all spelled out.

If anything, the measured progression of cuts provides a bit of certainty in the chaos of the hotter, drier, more unpredictable future we face.

So, while I know everyone will be talking about this first shortage because it’s new, and for those who haven’t been following the situation, reading the words “water shortage” will seem scary, forgive me if I view it as old hat.

The Tier 1 declaration isn’t our problem. It’s the other numbers contained in the reports that also will be released on Aug. 16, which have turned grim with a speed that has surprised even the experts. The upstream Lake Powell is dropping quickly, thanks to already low lake levels and near-record low runoff this year. The lower Powell falls, the less water Lake Mead gets.

That’s our problem.

It’s likely that we are in for multiple years of 7.48 million acre-feet releases, down from the 8.23 million acre-feet (or more) releases on which we have come to rely. This is consequential, considering that until now we’ve only had one 7.48 million acre-feet release in 2014, when Lake Mead was nowhere near shortage levels.

Lake levels never recovered from that lower release.

Less water from Lake Powell is driving the tank

And now Mead, which is V-shaped, is significantly lower in elevation – meaning it takes progressively less water to lower lake levels. Multiple years of 7.48 million acre-feet releases will cause lake levels to plummet (the forecast already says two in a row are likely, and that there’s a decent chance of them continuing through 2025).

In fact, the latest modeling suggests there may be nearly a 40% chance of Lake Mead reaching a Tier 3 shortage – the most severe for which we have planned – by 2025.

And if the projections hold, the states that rely on Mead could be meeting as soon as November to decide what other actions we can take (likely, it’ll be even more cuts) to keep the lake from falling below a critically low level of 1,020 feet of elevation. The modeling suggests that if we do nothing additional, the lake could drop to near 1,000 feet in a worst case by 2025.

Consider that. Arizona could take its worst-case 720,000 acre-feet of cuts in a Tier 3 shortage and still the lake could tank.

We must conserve – and by “we,” I don’t just mean Arizona. Demand certainly drives part of the equation for why Mead is dropping, which means we all need to use less. Permanently.

But so does supply, and if the lake could get 750,000 acre-feet less than usual for several years – or maybe from here on out, in an effort to keep Lake Powell from tanking – this can’t just fall on Arizona’s shoulders, even if we are the state with the junior-most water rights.

Whatever we do, it must be a shared sacrifice

The good news is that other basin states seem to recognize this, that if the lakes have any hope at sustainability, it’s going to require an additional shared sacrifice to get them there.

What that sacrifice looks like is anyone’s guess. Everyone knows it will be painful, which also will make it hard for everyone to swallow. The name of the game will be to choose actions that everyone can live with, not one that everyone likes.

Because we’ve entered a new era of shortage. This is our reality, our new normal – and, in fact, it probably won’t be long before we consider a Tier 1 shortage as a time of excess.

It can and probably will get worse from here, and yes, we’re planning for that, too. So that when that day arrives, we can say we’ve got this.

It’s going to hurt. But there is no need to freak out.

Reach Allhands at joanna.allhands@arizonarepublic.com. On Twitter: @joannaallhands.