Researchers who warned of the Great Salt Lake’s 5-year demise neglected a major water source. Read Part 2.

Editor’s note • This is the second installment of a three-part series in partnership with Utah Public Radio exploring a widely publicized warning about the health of the Great Salt Lake and whether the two wet winters that followed have rescued the body of water from harm’s way. Read Part 1 here.

Part 2 • ‘Where does the water come from?’

The way Paul Brooks sees it, the people who live, love, work and play in the Salt Lake Valley are in exceptional company.

“If you go to the Yellow River, the Tigris and Euphrates, the Indus, the Ganges, the Brahmaputra,” said Brooks, a hydrologist and biogeochemist at the University of Utah, “all of the locations where people started coming together in large groups, and we had division of labor to agriculture and banking and arts and seamstresses and shoemakers and all sorts of different things — where a lot of people live together, it was in these snowmelt-fed river valleys.”

While most Utahns might not think of themselves in such epochal ways, Brooks said, most do easily recognize that — just like in those other civilizations — the water that is absolutely paramount to any society comes from the mountains by way of rainwater runoff and snowmelt.

In the Salt Lake Valley, that water often arrives within days of rainfall and within months of a snowstorm as it makes its way toward the Great Salt Lake. But Brooks said that’s not, in fact, where most of the water goes. Not at first, at least.

“It doesn’t run off the surface,” he said. “Most of the water goes into the ground.”

And there it stays, in the soil and porous rocks, hundreds and even thousands of feet under the surface, often moving toward the lake at just inches a day. At these rates, it can take years and even decades for a water molecule that once fell from the sky to reemerge in the lake, evaporate, and begin the cycle anew.

But when a Brigham Young University-led team of scientists and activists issued a much-publicized warning in early 2023 that the Great Salt Lake could potentially dry up in five years, the authors expressly acknowledged that their inflow estimates, based on direct precipitation and runoff, didn’t include groundwater.

That exclusion wasn’t trivial. And it wasn’t the only way that the authors’ extrapolations — which team members say were evaluated by many other scientists but were not subjected to a formal peer-review process — may have inadequately reflected a larger picture about the lake and its potential futures.

‘The role of groundwater becomes huge’

To understand why groundwater is such an important variable for the future trajectories of the Great Salt Lake, a good starting point is the U.S. military’s detonation of nuclear weapons in the Nevada desert, starting with the Jan. 27, 1951, airdrop of a Mark 4 nuclear bomb about 65 miles northwest of Las Vegas, an effort that was originally called “Operation Faust.”

That name was befitting of the ambiguous bargain between power and risk that came with nuclear testing. But the federal Atomic Energy Commission, which oversaw the tests, initially downplayed the dangers, asserting that perilous radiation levels were limited to areas within a few miles of the blasts.

In the decades to come, however, it became clear that the same westerly winds that reliably carry moisture from the Pacific Ocean to Utah’s mountains also carried the radioactive dust from these tests into communities far from the detonation sites. The fallout unleashed by these and other nuclear tests continue to circulate across the globe today.

Among these radioactive particles is an isotope called tritium, which enters the global water cycle as water vapor and precipitation and diminishes over time at a steady rate. That gives scientists like Brooks the ability to track how long it takes for the rain and snow that fall on Utah’s mountains to reach a catchment like the Great Salt Lake.

“We can’t track every water molecule, so we can only track the average age,” he said. “And the average throughout the western U.S., from all the sites that we’ve looked at, is 6.9 years.”

Kip Solomon, a University of Utah geologist who helped develop the process for using tritium to age and trace groundwater, said early estimates had 3% of the water in the Great Salt Lake coming straight through the ground to the lake’s boundaries. More recent estimates, based on tracing isotopes, suggested that number was actually about 15%.

But Solomon said that much of the water that ends up in the tributaries that feed the lake — the Bear, Weber and Jordan rivers — was also first held in the soil and rocks of the watershed, often for many years.

“Now, all of a sudden,” Solomon said, “the role of groundwater becomes huge, because, easily, something like half of all of that water, and potentially even more, has spent considerable time in the ground.”

While what happens to snowpacks in any given year — or even several years in a row — can have a substantial and nearly immediate impact on the Great Salt Lake, that’s not the only variable affecting the lake’s volume over time. How much is in the ground matters, too.

‘Salinity decreases as volume increases’

The effect of the slow movement of underground water can be seen through the rising and falling levels of wells in the region around the lake. When lake levels are up over periods of multiple years, wells in the watershed tend to be elevated, too. And when lake elevations are down, wells tend to be more depleted.

That correlation could be handy.

There is currently no model that shows what could happen to the Great Salt Lake itself under different climate warming scenarios — it may be possible to do, but scientists have focused their efforts elsewhere. The connection between groundwater and the lake, however, might offer another way to peer into Utah’s future.

It’s impossible to know whether a simulation will be right years on, so climate scientists test computer models by running the simulations backward to see how accurate they are at reflecting what actually happened in the past. And for groundwater, one of these simulations, the Community Earth System Model, has tracked closely with the measurements of water in the wells, and thus has mirrored the actual gradual decline of the lake over the past 50 years.

Run that simulation forward from 2020 on, and the model offers a range of possibilities for the lake’s future, including a small outlying chance of almost complete desiccation by 2030. That would be in line with the warning that got so much attention in 2023.

But the most likely scenarios the model simulated — far and away the most probable outcomes — suggest that the lake levels wouldn’t fall that far or that fast.

While the chances are exceptionally slim, according to the model, the most probable time frame for complete desiccation would begin around 2045, and that could happen simply as an outcome of global warming — irrespective of whether diversions for cities, industry and agriculture are curtailed.

More likely, according to the model, is that the lake’s decline could slow and level off in the latter part of this century.

Those outcomes echo the findings of Ibrahim Mohammed, a hydrologist and former NASA researcher who began modeling potential Great Salt Lake trajectories as a graduate student at Utah State University nearly 20 years ago.

“Salinity decreases as volume increases and vice versa,” Mohammed explained, noting that salt water evaporates slower than fresh water. As a result, he said, evaporation — the only significant place for water to go once it reaches the closed-basin lake — would likely slow down if the lake receded, making total desiccation even less likely.

‘Saved by a change in the weather’

The writers of the 2023 report that warned of the potential total desiccation of the Great Salt Lake had many recommendations for what state leaders could do to reduce that risk — and also plenty of advice for what not to do.

Among the “counterproductive interventions” they advised against was to simply “wait for rain.”

“The last time the lake almost hit rock bottom, we were saved by a change in the weather,” the authors noted, referencing a series of abnormally wet years in the early 1980s that increased runoff. But, they surmised, that wasn’t likely to happen again.

“Climate change has altered weather patterns,” they wrote, “decreasing precipitation throughout the American Southwest.”

To support that argument, the report’s authors cited a peer-reviewed study from the journal Geophysical Research Letters that revealed a decrease over the past 40 years in how often the atmosphere sets up in ways that tend to create cold and wet weather.

That study, however, was focused on the western United States as a whole — not the basins that feed the Great Salt Lake. Zooming in on the region surrounding the lake itself reveals a more nuanced picture: The same models that suggested a slight decrease in precipitation across the West also showed the Great Salt Lake basin with a mixed bag of wet and dry years.

Even when looking at the West as a whole, though, the study cited didn’t suggest high-precipitation years would stop altogether. Rather, it simply concluded that such years had been slightly less frequent over the past few decades.

It’s true that, at the time the authors published their report, it had been a while since there had been an exceptionally wet winter in the Great Salt Lake basin.

By some measurements, the two years preceding their stark warnings represented the most extreme period of drought in about a century, but the Great Salt Lake’s watershed has experienced droughts that were nearly so bad in the past. These periods usually last one or two years before giving way to wetter spans of time.

While it was certainly possible that a big snow year could have failed to materialize, and that an acute drought could have continued for five more years, it was not at all probable.

‘Good years following good years’

The overwhelming majority of Americans believe that climate change is happening, accept the broad scientific consensus that it is human-caused, and worry that it will harm future generations. That’s despite the fact that most Americans aren’t sure they have personally been affected by it yet.

Even in staunchly conservative Utah, according to surveys from the Yale Climate Opinion Maps project, 68% of adults agree that climate change is happening, and 64% believe it will harm future generations.

And, like most Americans, a majority of Utahns also agree global warming is primarily caused by human activities. But also like most Americans, Utahns appear to be more hesitant to conclude that they have been impacted — about 39% of adults in the Beehive State feel as though they have already been affected by global warming.

That may reflect the fact that, even as temperatures rise overall and other weather outcomes shift as a result, the extremes of weather generally change by fractions, not factors.

Heat records are often broken by tenths of degrees. Rainfall deficits are often measured in fragments of an inch. Changes in humidity, wind, cloud cover and other weather variables that have been connected to global warming increase and decrease over historical records by a little here and a little there.

As a result, the perceptible effect of climate warming can be hard for any person to distinguish. And even what might seem to be an extreme shift in any one instance may fall within underlying variability — the broad range of meteorological possibilities that have always occurred, even before humans released so many greenhouse gasses into the atmosphere.

The same is true of drought in the Mountain West. Research, such as a 2020 study from a team from Utah, Arizona, Colorado, Nevada and Montana, strongly suggests that warming has caused — and will likely continue to cause — more severe and possibly longer periods of acute drought. But few if any studies have suggested that natural variability would cease to be the dominant force driving yearly and multiyear fluctuations.

It’s thus no surprise that the drought that came ahead of the 2023 BYU report had lasted as long as it did. But it would not have simply been historic if it had lasted five more years — it also would have obliterated the old record beyond recognition.

It’s not that the climatological factors influencing snowpacks and resultant water levels in the Great Salt Lake hadn’t changed at all. They had.

“You know, back in the ‘80s, we had good years following good years, and that really fills in the lake when that happens,” said Craig Miller, the hydrology and modeling manager for the Utah Division of Water Resources. “The last couple of decades, whenever we have a great water year, the next year is just so-so.”

Although the general trend over the past few decades has been fewer back-to-back wet winters, Miller noted, the one-and-done good water years haven’t disappeared altogether. Indeed, two of the top 10 water years on record in Salt Lake City came in the 2010s, according to the National Weather Service.

It cannot be said that the region surrounding the Great Salt Lake was “overdue” for a big year — because that’s not how probability works. It was nonetheless likely that, sooner or later, the random forces at play would send a big winter to the mountains surrounding the lake.

And that’s what happened in the weeks and months immediately after the release of the five-year warning.

None of this means that continued diversions — which the writers of the much-publicized report warned were responsible for the lake’s potential desiccation — don’t matter. Clearly, the lake’s likely long-term recession could speed up if water continues to be wasted, whether it is pulled from streams and rivers, thus affecting the lake immediately, or it is drawn from the ground, thus impacting the lake years later.

What it does mean, however, is that the Great Salt Lake’s fate is not purely in the hands of the Utahns who control how much water is diverted. Its future is also dependent on whether greenhouse gas emissions around the world are curtailed, by how much, and by how soon.

Coming in Part 3 • In a world where climate changes by fractions, not factors, would a more nuanced warning about the Great Salt Lake have stirred action?

Editor’s note • This story is available to Salt Lake Tribune subscribers only. Thank you for supporting local journalism.

Matthew D. LaPlante is a climate scientist and associate professor of journalism at Utah State University. He is a former staff reporter for The Salt Lake Tribune and the host of the science-themed program “UnDisciplined” on Utah Public Radio. The show will release three episodes to accompany this series.

LaPlante is the co-author, along with Piyush Dahal, Shih-Yu Simon Wang, Kirsti Hakala, and Avik Mukherjee, of the peer-reviewed study “A ‘nuclear bomb’ or just ‘a joke’? Groundwater models may help communicate nuanced risks to the Great Salt Lake,” which was published in the journal Water on Aug. 6. None of the individuals quoted in this series was involved in the study.