Click the link to read the article on the Grist website (Jake Bittle & Daniel Penner):

California and Arizona are currently fighting each other over water from the Colorado River. But this isn’t new — it’s actually been going on for over 100 years. At one point, the states literally went to war about it. The problem comes down to some really bad math from 1922.

To some extent, the crisis can be blamed on climate change. The West is in the middle of a once-in-a-millennium drought. As temperatures rise, the snow pack that feeds the river has gotten much thinner, and the river’s main reservoirs have all but dried up. 

But that’s only part of the story: The United States has also been overusing the Colorado for more than a century thanks to a byzantine set of flawed laws and lawsuits known as the “Law of the River.” This legal tangle not only has been over-allocating the river, it also has been driving conflict in the region, especially between the two biggest users, California and Arizona, which are both trying to secure as much water as they can. And now, as a massive drought grips the region, the law of the river has reached a breaking point.

The Colorado River begins in the Rocky Mountains and winds its way southwest, twisting through the Grand Canyon and entering the Pacific at Baja California. In the late 19th century, as white settlers arrived in the West, they started diverting water from the mighty river to irrigate their crops, funneling it through dirt canals. For a little while, this worked really well. The canals made an industrial farming mecca out of desert that early colonial settlers viewed as “worthless.”

Even back then, the biggest water users were Arizona and California, which took so much water that they started to drain the river farther upstream, literally drying it out. According to American legal precedent, whoever uses a body of water first usually has the strongest rights to it. But other states soon cried foul: California was growing much faster than they were, and they believed it wasn’t fair that the Golden State should suck up all the water before they got a chance to develop. 

In 1922, the states came to a solution — kind of. At the suggestion of a newly appointed cabinet secretary named Herbert Hoover, the states agreed to split the river into two sections, drawing an arbitrary line halfway along its length at a spot called Lee Ferry. The states on the “upper” part of the river — Colorado, Utah, Wyoming, and New Mexico — agreed to send the states on the “lower” end of the river — Arizona, California, and Nevada — what they thought was half the river’s overall flow, 7.5 million acre-feet of water each year. (An acre-foot is enough to cover an acre of land in a foot of water, about enough to supply two homes for a year.)

This agreement was supposed to prevent any one state from drying up the river before the other states could use it. The Upper Basin states got half and the Lower Basin states got half. Simple.

But there were some serious flaws to this plan. 

First, the Law of the River overestimated how much water flowed through the river in the first place. The states’ numbers were based on primitive data from stream gauges placed at arbitrary points on the waterway, and they took samples during an unusually wet decade, leading to a very optimistic estimate of the river’s size. The river would only average about 14 million acre-feet annually, but the agreement handed out 15 million to the seven states.

While the states weren’t able to immediately use all this water, it set in motion the underlying problem today: The states have the legal right to use more water than actually exists in the river.

And you’ll notice that the Colorado River doesn’t end in the U.S. — It ends in Mexico. Initially, the Law of the River just straight-up ignored that fact. Decades later, Mexico was squeezed into the agreement and promised 1.5 million acre-feet, further straining the already over-allocated river.

On top of all of this, Indigenous tribes that had depended on the river for centuries were now forced to compete with states for their share of water, leading to these drawn-out lawsuits that took decades to resolve.

But in the short-term, Arizona and California struck it rich — they were promised the largest share of Colorado River water and should have been primed for growth. For Arizona, though, there was a catch: The state couldn’t put their water to use.

The state’s biggest population centers in Phoenix and Tucson were hundreds of miles away from the river itself, and it would take a 300-mile canal to bring the water across the desert — something the state couldn’t afford to build on its own. Larger and wealthier California was able to build all the canals and pumps it needed to divert river water to farms and cities. This allowed it to gulp up both its share and the extra Lower Basin water that Arizona couldn’t access. California’s powerful congressional delegation lobbied to stop Congress from approving Arizona’s canal project, as the state wanted to keep the Colorado River to itself.

Arizona was furious. And so, in 1934, Arizona and California went to war — literally. Arizona tried to block California from building new dams to take more water from the river, using “military” force when necessary.

Arizona sent troops from its National Guard to stop California from building the Parker Dam. It delayed construction, but not for very long because their boat got tangled up in some electrical wire and had to be rescued.

For the next 30 years, Arizona and California fought about whether Arizona should be able to build that canal. They also sued each other before the Supreme Court no fewer than 10 times, including one 1963 case that set the record for the longest oral arguments in the history of the modern court, taking 16 hours over four days and involving 106 witnesses.

That 1963 case also made some pretty big assumptions: Even though the states now knew that the initial estimates were too high, the court-appointed expert said he was “morally certain that neither in my lifetime, nor in your lifetime, nor the lifetime of your children and great-grandchildren will there be an inadequate supply of water” from the river for California’s cities.

A few years after that court case, in 1968, Arizona finally struck a fateful bargain to ensure it could claim its share of the river. California gave up its anti-canal campaign and the federal government agreed to pay for the construction of the 300-mile project that would bring Colorado River water across the desert to Phoenix. This move helped save Arizona’s cotton-farming industry and enabled Phoenix to eventually grow into the fifth-largest city in the country. It seemed like a success — Arizona was flourishing! 

But in exchange for the canal, the state made a fateful concession: If the reservoirs at Lake Powell and Lake Mead were to run low, Arizona, and not California, would be the first state to make cuts. It was a decision the state’s leaders would come to regret.

In the early 2000s, as a massive drought gripped the Southwest, water levels in the river’s two key reservoirs dropped. Now that both Arizona and California were fully using their shares of the river, combined with the other states’ usage, there suddenly wasn’t enough melting snow to fill the reservoirs back up. A shrinking Colorado River couldn’t keep up with a century of rising demand.

Today, more than 20 years into the drought, Arizona has had to bear the biggest burden. Thanks to its earlier compromise decades earlier, the state had “junior water rights,” meaning it took the first cuts as part of the drought plan. In 2021, those cuts officially went into effect, drying out cotton and alfalfa fields across the central part of the state until much of the landscape turned brown. Still, those cuts haven’t been enough.

This century, the river is only averaging around 12.4 million acre-feet. The Upper Basin states technically have the rights to 7.5 million acre-feet, but they only use about half of that. In the Lower Basin, meanwhile, Arizona and California are gobbling up around three and four million acre-feet respectively. In total, this overdraft has caused reservoir levels to fall. It’s going to take a lot more than a few rainy seasons to fix this problem.

So, for the first time since the Law of the River was written, the federal government has had to step in, ordering the states to reduce total water usage on the river, this time by nearly a third. That’s a jaw-dropping demand!

These new cuts will extend to Arizona, California, and beyond, drying up thousands more acres of farmland, not to mention cities around Phoenix and Los Angeles that rely on the Colorado River. These new restrictions will also put increased pressure on the many tribes that have used the Colorado River for centuries: Tribes that have water rights will be pressured to sell or lease them to other water users, and tribes without recognized water rights will face increased opposition as they try to secure their share.

And Arizona and California are still fighting over who should bear the biggest burden of these new cuts. California has insisted that the Law of the River requires Arizona to shoulder the pain, and from a legal standpoint they may be right. But Arizona says further cuts would be disastrous for the state’s economy, and the other five river states are taking its side.

Either way, the painful cuts have to come from somewhere, because the Law of the River was built on math that doesn’t add up.

Click the link to read the article on the Sibley’s Rivers website (George Sibley):

As you no doubt already know, if you follow Colorado River news, the Bureau of Reclamation and Department of Interior have issued a ‘Near-term Colorado River Operations: Supplemental Environmental Impact Statement’ (SEIS) analyzing two alternatives for making massive cuts in the consumptive use of the Colorado River’s waters, beginning in 2024. The SEIS analyzes strategies for cutting use by two million-acre feet (maf) next year, with cuts up to four maf in following years if the water supply in storage continues to decline – roughly a third of the total volume of the river as it has run since the turn of the century.

​The alternatives discussed in the SEIS will look familiar to those who have followed the river news for the past couple months; they are similar to the plans for large reductions created by the seven River Basin states: one plan by six of the states, the other by the seventh, California. One of the Bureau’s ‘action alternatives’ divides the big cuts equitably among the three states based on the size of their allotments, like the six states’ plan; the other adheres mostly to priority of water rights in dishing out the cuts, like the California plan.

If there is anything to be learned for the future from the past, it should be noted now that this sudden dramatic need for really major cuts in consumptive use in the lower part of the river basin is the consequence of problems that could have been dealt with gradually – intelligently, one might say, far-sightedly – over at least the past 30 years, if not the whole last century since the discovery that the Colorado River Compact was based on false numbers.

​But through the 1940s and 50s, there was a lovely sense of abundant water in the Lower Basin. The four states of the Upper Basin were considerably slower in developing than the three in the Lower Basin, so a lot of the river was still flowing freely to the desert states below the canyons and eventually being ‘wasted’ to the ocean, then regarded as a sad end for freshwater.

​Even before Hoover Dam was completed, the Californians, with Bureau permission, decided to borrow some of that water to grow on – with really no firm plan about what to do when the Upper Basin developed its water. They did not really know how much (or how little) water the river really carried, and the spirit of the times decreed that the engineers would figure something out to solve the problems of the future. California’s 1931 ‘Seven Parties Agreement’ divvied up more than 900,000 af  of borrowed water – and built their permanent systems large enough to carry that along with their legal allotment.

The Lower Basin states were also, kind of semiconsciously, depending on that ‘surplus’ water to cover all of the substantial ‘system losses’ in the Lower Basin – evaporation and conveyance losses – and also the Lower Basin’s 750,000 af share of the commitment to Mexico: all told, at least 2 maf of water for which the Lower Basin states were accountable, but none of which was deducted from their allotments as set by the Boulder Canyon Project Act. They developed their 7.5 maf Compact allotment to the max, and this ambiguous but very real 2 maf became known as ‘a structural deficit,’ as though it were just inherent in the structure of the system and nothing could be done about it, not unlike an Act of God.

​But the Upper Basin states eventually got up to around 4 maf of consumptive use (including Upper Basina system losses) late in the century, with big out-of-basin projects like the Colorado-Big Thompson, San Juan-Chama, Dillion Reservoir, Homestake, and Arizona’s big Central Arizona Project came on line in 1993 – and everyone knew by then how little water the river actually carried, with no big river augmentation projects on the horizon…. Common sense would seem to dictate that, at least by the 1990s, the Californians would have begun a schedule for weaning themselves from the borrowed water, and all three Lower Basin states would have begun figuring out how to deal with the ‘structural deficit.’ But that kind of sense was of course completely contrary to the naive energies of the Early Anthropocene that still prevailed in the Basin, and the Lower Basin states – graciously enabled by the Bureau – continued using consumptively somewhere around 800,000 af of borrowed Upper Basin water in addition to their full 7.5 maf Compact allotments, and ignoring any responsibility for the 2 maf structural deficit.

​The water, by then, was no longer flowing freely through the canyons to the Lower Basin, but was being released by the Bureau from Powell Reservoir, requiring some complex definitions of ‘surplus’ – possibly trying to disguise its decline – and some big water years in the 1980s and 90s allowed them to continue to cover the profligate release of more than 10 maf to cover Lower Basin’s legal allotments, plus borrowings, plus ignored system losses.

But the climate and the river turned against them with the turn of the century. For the five water years 2000-2004, inflows into Powell Reservoir averaged a measly 6 maf, less than two-thirds the 20th-century average inflows. Meanwhile, however, the Bureau continued to release more than 8 maf annually from Powell to Mead, and then the usual Compact allocation plus borrowings from Mead to the desert states with no accounting for the system losses: basically, 6 maf in, and 10+ maf out of the system. Predictably enough, storage took a dive in both reservoirs, and everyone realized that something different needed to be done soon.

​The first thing done was in 2003; Interior Secretary Gale Norton, mustered the gumption to tell California that it was time to stop borrowing no-longer-existing surplus water. To the surprise of all the Caliphobics, California complied, and began to work its way back to its 4.4 maf allotment. But nothing was said then about the ‘structural deficit,’ so between their full consumptive use of their 7.5 maf Compact allotment, and the 2 maf of system losses and Mexican obligations for which they continued to decline responsibility, the Lower Basin states were still consuming between nine and ten million acre-feet annually; storage was still declining and something really different still needed to be done.

For two years representatives from the seven states and other stakeholders met with the Bureau, to address that need, and the result was a 2007 agreement called ‘Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead.’ This was essentially an attempt to try out some ideas for more carefully coordinating the use of the two big reservoirs while encouraging Lower Basin users to cut their use and leave some of their water in Mead (‘Intentionally Created Surpluses), making it possible to draw less from Powell. The ‘interim’ for these temporary guidelines was the 20 years to 2026, at which time, according to plan or hope, the Bureau and the seven states would have developed a new longterm management regime that actually incorporated the realities of a desert river.

​The Interim Guidelines rely on a ‘balancing’ of the water in the two reservoirs, to keep both reservoir levels high enough so the generation of electric power can continue – an elevation of 3,490 feet (above sea level) for Powell Reservoir and 1,000 feet for Mead Reservoir. And if that proved to be impossible in an extended period of aridification, then the last-ditch effort would be to keep levels above each reservoir’s outlet works – an elevation of 3,370 feet in Powell and 895 feet in Mead. If the reservoirs fell below those outlet levels for either dam, then it would be impossible to convey any water at all beyond the dam. Dead pool.

A complex table of ‘Lake Powell Operational Tiers’ is the heart of the Interim Guidelines, defining the various levels at which releases from Powell should increase or decrease depending on both the level in Powell and how the level in Mead was increasing or (generally) decreasing. And if levels continued to decline (which they have), the grinding gut of the Interim Guidelines is a set of ‘shortage conditions’ – levels at which delivery cuts will be imposed on the Lower Basin states. In 2022, the Bureau finally acknowledged the reality of the situation and declared the first level of cuts, on Arizona and Nevada.

​Why not California too? More history: Back in 1968, when Arizona was lobbying desperately for approval of the legislation that would finally enable the CAP, California had said that it would only support the project if Arizona would accept a junior status for the CAP to all of California’s Colorado River water rights. For Arizona, even in the late 1960s, that seemed like a gamble worth taking; who could imagine water shortages that might shut down Hoover Dam and the vast array of urban-industrial development it watered? So the Arizonans agreed to California’s condition – and half a century later the unimaginable happened.

But California did not entirely employ the Shylock gambit; they reluctantly agreed in a neighborly way to accept some Interim Guideline cuts before Central Arizona was completely dried up; their cuts begin at about the fourth level of escalating cuts for Arizona and Nevada.

​Everywhere in the Colorado River region today, it is entirely too easy to get lost in the numbers, all those abstract thousands and millions of acre-feet. Suffice it to say for now that under the Interim Guidelines, by the time the balanced levels of Powell and Mead Reservoirs dropped to within 30-40 feet of the power generation cutoff levels, central Arizona would be giving up 720,000 af, Nevada 30,000 af, and California 350,000 af, for a total of 1.1 maf. Substantial pain – but only about half of the 2 maf structural deficit, the number to keep in mind for this unfolding melodrama. Because there is simply no way, short of constant climate miracles, to avoid an eventual dead-pool situation if the Lower Basin continues ignoring the structural deficit, with inflows to Powell way below the outflows plus system losses from the Lower Basin storage and distribution systems.

What about the Upper Basin states? They get a bye on this round. For one thing, the federal government does not control their water supply, nature does; and they are also way under their 7.5 maf Compact allotment. Also since the beginning of the drought period, the Bureau had already let more than 10 maf of ‘their’ water flow down to Mead above and beyond the Compact requirement. They also have no ‘structural deficit’; their usage includes their system losses – although the half-million acre-feet, plus or minus, evaporated out of Powell should probably be included in the unaccounted-for reservoir system losses since it occurs after the measured inflow. But people in the Upper Basin know their opportunity to participate in the reductions will come.

Even as the first level of shortages was being executed on Arizona and Nevada in 2022 (with the second level promised for this year), Powell was in its third consecutive year of inflows of 6 maf or less with outflows and system losses from Mead still in excess of 9 maf, and the Bureau realized that even the Interim Guidelines reductions might not get them all the way to 2026. Facing that, the Bureau and Interior Secretary issued a somewhat desperate announcement that it would be necessary to quickly implement much heavier cuts – at least two and maybe four million acre-feet. The Bureau Director and Interior Secretary asked the seven states to come up with a plan for how that might happen – and said that if the states did not come up with a plan, they would impose one of their own.

​They actually said this twice, midsummer in 2022, and midwinter in 2023; the first time I think the states were too stunned to respond, and no plans emerged from either the states or the Bureau. But now, after the second call, there are four alternatives on the table, two from the states and two from the Bureau. Two of these alternatives argue for using the foundational ‘Law of the River,’ the appropriation doctrine, to distribute the necessary cuts; a big faction (mostly those with senior water rights) believes appropriations law can and should resolve every issue involving water in the arid West.

The other two alternatives seem to see the 2 maf structural deficit as a foundational mistake that needs to be corrected outside or below the rules governing the use of the river’s water; the structural deficit is water that isn’t there to use, and therefore shouldn’t be dealt with through the laws for the use of water. It thus makes the most sense to share those ‘structural’ losses out proportionally among the three states rather than trying to apply the use-allocation law to them.

​It is clear enough that the resolution will have to involve a middle ground, similar to that arrived at in the Interim Guidelines, when California’s priority was acknowledged but the state conceded to take some cuts before completely drying up the CAP. The Bureau’s second alternative comes closest to seeking that middle ground. If it were implemented, that accommodation to seniority would be carried forward with reduced assessments to California despite their use of more than half the Lower Basin’s water. In getting to the 2.083 maf goal, Arizona would take the hardest hit (1.087 maf), more than a third of their 2.8 maf allotment; and California would lose 927,000 af, only a fifth of their 4.4 maf allotment. Nevada would lose 69,000 af, about a fourth of their 300,000 af allotment.

Ultimately something along those lines has to sound better to California than going to court on principle for the usual decade, and driving the river into a dead-pool status under which they would get no water at all much of the year. Laws that can’t bend or open up to fit changing situations eventually break under the stress.

​And then – well, the 20-year interim period for the water mavens to figure out what to do for the next century has shrunk to three years. And the last I heard, they are still trying to figure out who does and doesn’t get to sit at the table to figure it out the future.

​The Bureau encourages comments on the SEIS, by May 30: Crinterimops@usbr.gov.