The U.S. Western states are in a megadrought that scientists don't expect to end for another 700 years or so, if history repeats itself. Here's a story from an expert writing for Quora who explains how the west made a mistake with water rights.
(Images: As of August 22, 2021, Lake Mead was filled to just 35 percent of its capacity. The low water level comes at a time when 95 percent of the land in nine Western states is affected by some level of drought (64 percent is extreme or worse). It continues a 22-year megadrought that may be the region’s worst dry spell in twelve centuries. These natural-color images were acquired in August 2000 and August 2021 by Landsat 7 and Landsat 8. The tan fringes along the shoreline in 2021 are areas of the lakebed that would be underwater when the reservoir is filled closer to capacity. The phenomenon is often referred to as a “bathtub ring.” Credit: NASA)
Source; Quora.com July 7, 2022
Most of the trouble the Colorado River watershed is facing is because of a bad guess made one hundred years ago.
In 1922 the states of California, Nevada, Utah, Wyoming, Colorado and New Mexico made an agreement to to manage Colorado River water. They needed a definite number to peg the average annual flow of the river to, and chose to set it at 15 million acre-feet per year. They based this on flow gauges that had measured at least 17 million acre-feet a year since 1890.
But that was an overestimate; the Colorado watershed happened to be going through a wet spell. The actual reliable number for the 20th century was more like 13 million acre-feet (about 500 cubic meters per second).
In 1944 Mexico got Congress to ratify a treaty guaranteeing it 1.5 million acre-feet of Colorado River water. They had been trying ever since the 1922 agreement, but 1944 was a good year to press Congress since it was a wartime year and the US needed Mexican cooperation in shipping defense. The state of Arizona took the opportunity to claim a share of the 15 million acre-feet of the 1922 agreement, partly to assure they wouldn’t later lose water to California. The total committed flow of the Colorado was now 16.5 million acre-feet — on paper. Actual use ranged closer to 6 million acre-feet, mostly by California.
For most of the early 20th century the Colorado seemed inexhaustible; nobody was using their full share of water and everyone had a comfortable margin in case of drought.
Come the 1950s though, new plans to exploit the river’s water to within a tenth of assumed capacity were put forth: the 1956 Colorado River Storage Project.
Like its sibling the 1957 Interstate Highway Project, this plan would create vast new infrastructure encouraging settlement of America’s West. New dams and reservoirs, new canals and powerlines would “reclaim” arid land for agriculture and urbanization, after the fashion of California’s Los Angeles basin development but bigger.
There was just one problem: that inflated flow number was baked into the plan.
For the next 24 years everyone worked on the assumption they were dividing up 16.5 million acre-feet of water a year, even as evidence mounted that the river couldn’t supply that. Phoenix grew into a major city surrounded by cheap salad — so much lettuce now grew in Arizona that it pushed longtime growers in other parts of the country out of business.
Then in the 1990s the region got a wakeup call.
There had been severe droughts over the decades. Seeking the cause of those droughts, water planners had stumbled onto the weird world of tree ring analysis and Carbon-14.
All living things absorb Carbon-14 then mostly stop absorbing it when they die. Carbon-14 is radioactive and steadily decays to Nitrogen-14. Measuring how much Carbon-14 remains in dead organic matter can tell you how long it’s been dead — if you know how much Carbon-14 that dead thing was absorbing when alive. That includes knowing how quickly it grew.
In order to make their Carbon-14 dating accurate, paleontologists had to study ancient climate going back over 15,000 years. Part of this was accurately charting temperature and moisture fluctuations in order to estimate how quickly plants grew.
There was no one indicator in the geologic record, but an important early indicator were growth rings in a strange little tree called the Bristlecone Pine.
This tree, a stubborn holdover from Ice Age times, grows in isolated pockets throughout the Southwest and can live for over three thousand years. The pines lay down thousands of annual growth rings in their wood that are wider in wet warm years and thinner in dry cool years.
In a supreme feat of detective work, researchers matched patterns of thin and thick rings in these pines to similar patterns found in wood of known ages across America, some of it long dead, and then extended this to study of even older semi-fossilized wood as well as lake floor sediments and other indicators.
And as they did so they also wrote computer programs that modeled the factors controlling wood growth and adjusted them until they matched the paleontological record. By the 1990s these programs were reliable enough to predict growing conditions in any location in the American West in the past 15,000 years, and could even be run forward to predict future conditions.
And as they did this it was noticed that the Colorado watershed undergoes long cycles of damp to dry conditions. Nothing as neat as a calendar, but generally an 800-year cycle from dry to wet to dry again.
1922 had been near the peak of the damp side of the cycle. And ever since then the watershed had been getting drier.
Here in 2022 the watershed is well on the way into a longterm drying that hasn’t hit bottom yet.
Ironically, if we hadn’t massively ramped up consumption in the 1950s through 1980s we’d be sitting pretty right now. Lake Mead would be almost full, there would be no calls for drastic conservation measures. Our 6 million acre-foot 1950 level of consumption wouldn’t have been reached yet today.
But it offended our Fifties sensibilities to waste all that water and all that land. Why let extra spill into the sea? Postwar world population was on a sharp 22%-a-decade growth trend, so everyone knew the population would would at least double within forty years. A popular book dubbed this The Population Bomb.
How could we ever feed so many new mouths without drastic expansion of farmland, of irrigation? If not for US need but world need, we felt a duty to expand food production to the limit.
Thing is, the land put under irrigation mostly wasn’t suitable for basic foodstuffs like maize or wheat or potatoes. You could grow them but they cost more to produce and ship than they’d bring at market. It was truck vegetables, the tomatoes and lettuce and cucumbers and spinach that paid to grow there.
But these already grew well elsewhere, so to create a market for Colorado watershed veggies the US government helped crush the competition.
“Crush” my seem a strong word but all over America, existing grow operations that hadn’t already been outcompeted by California vegetables found their best customers, the supermarket chains turning to Arizona sources with federal encouragement.
The Colorado River Storage Project needed to show a benefit to fulfil its congressional mandate, and this way it did…for a while.
And now? The water consumption is at clearly unsustainable levels, mostly to support unnecessary agriculture. Those farms support jobs, but no more than regional growers would have before Arizona forced them off the market. World food production has kept pace after all, and with 8 billion people we now have less hunger than in 1950 when we had 2.5 billion to feed.
For Lake Mead to remain a lake those truck farms have to be closed and replanted with native vegetation to hold the soil—soon.
But that would take political will that Arizona is still lacking, thanks to strong lobbying by present water consumers, present land developers. In the present political climate, state government is stuffed with people stubbornly refusing to face facts or make plans, eager to deflect and deny, all to give a few big investors a chance to make some more money before it all hits the fan.
Well, this is the decade it all hits the fan.
The numbers tell us that Lake Mead runs effectively dry by 2030 if nothing changes. Before then the farms all fail and turn to dustbowls, and Phoenix and Las Vegas will disappear under the ensuing dust.
This decade. Now. Unless we act.
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