In the second half of the 20th century, the Aral Sea – once the fourth largest lake in the world by surface area – began visibly shrinking as the rivers entering the central Asian saline lake, which straddles the border between Kazakhstan and Uzbekistan, were diverted to irrigate agriculture. Today, the Aral Sea is all but gone, in one of Earth’s most dramatic hydrological transformations of recent times.

Now the same thing may be happening to Utah’s Great Salt Lake. The inland sea, which in places is eight times saltier than the ocean, fell to its lowest level in recorded history in November 2016, and now contains just the half the water it did in 1847, according to an analysis published in October in the journal Nature Geoscience. This loss of volume corresponds to an 11ft (3.3m) drop in the lake’s surface elevation and an approximately 50 percent decline in surface area from historic levels, according to the research.

The analysis found human use of water to be the cause of the lake’s decline. It lends weight to ongoing calls from environmentalists to slow diversions from the lake’s inflow rivers, which supply farmland and millions of people with water.

A Shrinking Lake

As with rivers in just about every developed part of the world, those that enter Great Salt Lake are used by farmers and cities in the surrounding basin. According to the recent Nature Geoscience research – which was led by Wayne Wurtsbaugh, a Utah State University professor of watershed sciences – this demand for water has significantly reduced input from Great Salt Lake’s three primary supply rivers, the Bear, Jordan and Weber.

As a result, evaporation from the lake’s surface is considerably outpacing river inflow. As the lake shrinks, wildlife habitat is disappearing and airborne dust from the exposed, dried lakebed threatens the health of the two million people in the surrounding area, including Salt Lake City, according to Wurtsbaugh and his co-authors.

The scientists analyzed tree-ring data and other indicators of local historical climate and found neither climate change nor natural hydrological cycles to be responsible for the diminishing of the lake. This, they concluded, puts the onus on water managers to strike a sustainable water budget among urban and agricultural users in the lake’s basin to prevent the level from dropping further.

Co-author Sarah Null, an associate professor of watershed sciences at USU, argues that some level of impact to lakes like the Great Salt Lake is unavoidable in developed areas.

“I do not think that it is feasible for saline lakes to be completely unaffected by humans and water development,” she said in an email. “However, it is feasible to develop lake levels that are compromises between maintaining lake ecosystems and developing water.” She and her colleagues have recommended increasing river flows into Great Salt Lake by 29 percent to stabilize its surface elevation.

Competing Interests

It is unclear how this objective is compatible with proposed plans to build several dams on the Bear River, Great Salt Lake’s largest feeder stream. The dams could annually divert 220,000 acre-feet, or more, of water that would otherwise reach the lake. That would reduce the already impacted inflow by another 20 percent.

Zachary Frankel, executive director of the Utah Rivers Council, says this project’s potential impacts have been grossly underestimated by state officials and scientists. Frankel believes a widely repeated forecast of the lake declining by 8.5 inches if the dams are built – an estimate from the Utah Division of Water Resources – is an underestimate.

“That number is a wishful fallacy,” said Frankel, who worries the diversions could cause several feet of surface elevation loss. That, he warns, would devastate the wetland habitat used by 8-10 million migrating birds every year.

But Craig Miller, an engineer with the division who helped calculate the project’s impacts on the lake, says much of the water diverted from the Bear River will be used for indoor urban use and irrigation, and most of that will return to the lake eventually. He told Water Deeply that only 85,000 to 86,000 acre-feet of water would be lost to evaporation each year because of the project.

Frankel, skeptical of these numbers, alleges that private interests – especially engineering companies and water districts – are promoting the project, which could cost $2 billion.

Officials have said Utah’s population – forecast to almost double to 5.5 million by 2065 – calls for new water development projects, though Frankel believes the state’s Division of Water Resources (DWR) has not adequately pursued conservation. Utah currently boasts one of the highest rates of domestic water use per capita in the country. Data from the United States Geological Survey shows Utah residents using 167 gallons per person per day in 2010. Only Idaho is higher at 168 gallons per person per day.

However, Utah’s Office of the Legislative Auditor General released an audit in 2015 that questioned the accuracy of water use statistics, especially state projections that residents would use 220 gallons per day decades into the future. The audit noted that conservation efforts would likely draw down consumption significantly. The audit also noted that trends of developing farmland would free a great deal of water currently used for irrigation, which the DWR has reported amounts to 82 percent of Utah’s total water use.

“We aren’t running out of water,” said Frankel, who agrees with the auditor’s criticisms. “There’s no need for this project. Special interests are pressuring legislators to build it.”

But Marisa Egbert, the DWR’s Bear River development planning manager, said the need for water was very real. While conservation and agricultural-to-residential conversions would ease demand, that would only delay what was probably inevitable. “Our numbers are showing that there is an eventual need for water,” she said.

Egbert said the deadline for the project, based on projected demand, “keeps getting pushed back,” thanks to conservation efforts and farmland retirement. In the 1990s, she said, water managers thought the project would be needed by 2015. “Well, here we are two years later, and now they’re saying 2050.”

Disappearing Saline Lakes

Saline lakes around the world are giving way to the pressures of human demand. The Aral Sea may be the most dramatic example, with at least 90 percent of the lake’s historic surface area gone and 75 percent of its total volume sacrificed to intensive agricultural production. Today, barren sand dunes in the Aral basin are strewn with abandoned boats and decaying fishing gear. Lake Urmia in Iran has been similarly affected by diversions.

In California, the Salton Sea, fed by agricultural runoff, has rapidly shrunk after a large water transfer diverted the Colorado River from nearby farm fields to urban areas in San Diego County. Salinity levels have spiked, and fish and shorebird numbers have plunged. According to the California Air Resources Board, hazardous particulate concentrations in the air are three to four times above safe levels in the Salton Sea basin.

A similar health threat has taken shape in the eastern Sierra Nevada, where dry, dusty flats surround the shallow briny remnants of Owens Lake, which was drained to divert water to Los Angeles in the early 20th century.

In the Great Salt Lake basin, air quality is bad and growing worse. Derek Mallia, a researcher with the USU’s Department of Atmospheric Sciences, has calculated that airborne concentrations of harmful particulates could jump nearly 300 percent in some locations during dust storms if the Bear River development proceeds as planned. In an email, he said not going ahead with the diversion project “is the only plausible way of not exacerbating the dust issue.”

In their Nature Geoscience article, Wurtsbaugh, Null and their co-authors estimate that runoff in the Great Salt Lake basin will decline by 11–20 percent by the middle of this century as a result of climate change. (Since 1847, net inflows have already dropped by about 40 percent, according to the researchers.)

The long-term outlook for Great Salt Lake is not good. Still, it is not exactly facing a death sentence. In a 2016 white paper Wurtsbaugh, Null and others explain how, as a saline lake’s level falls, its surface area decreases, reducing the capacity for evaporative losses. Salinity also increases, which further slows evaporation. All principles of physics considered, the scientists predicted that “if there was a 25 percent decrease in streamflow to the lake, its elevation would slowly drop and, after 15 years, equilibrate at an elevation about 2.2 feet lower.”

On the other hand, Null said, reduced human use of water in the order of 29 percent would actually increase the level of the lake, and “protect most lake ecosystems.”