Utah’s Great Salt Lake has lost half its water, thanks to thirsty humans

The world’s saltwater lakes are drying up and scientists have long suspected climate change was to blame. Now, a study reveals another potential culprit: thirsty humans. According to more than 170 years of water records and a comparison of how much water flows in and out of the lake, consumption of freshwater is likely to blame for the shrinking of Utah’s Great Salt Lake—and of similar lakes around the world.

Since 1847, the Great Salt Lake has steadily shrunk, reaching its lowest recorded level in 2016. Today, the lake is 3.6 meters below its 1847 level and just half its original volume. Previously, many researchers thought the decline—here and in other saltwater lakes—was caused by wet and dry cycles related to climate change, says Wayne Wurtsbaugh, a limnologist at Utah State University in Logan.

To test that notion, Wurtsbaugh and his colleagues recreated the climate around the Great Salt Lake for 170 years, based on historical precipitation, stream level records, and tree ring data. The records showed that precipitation and temperature patterns had hardly fluctuated during the period, meaning that the amount of water flowing into the lake from nearby streams is likely the same today as it was in 1847. Next, the team did some hydrological accounting, creating what’s known as a water balance. They compared the amount of water flowing into the lake from rivers, precipitation, and groundwater to the amount evaporating out of the lake; if the lake stayed the same size, the water in and out should balance. It didn’t.

Why? Every year, people living in the region (which includes rapidly growing Salt Lake City) divert 3.3 trillion liters of water, not from the lake itself, but from the handful of streams feeding it. With climate staying relatively stable, the team concluded that humans are triggering the decline by consuming streamwater before it replenishes the lake, they reported last week in Nature Geoscience . Although some of that water returns to the lake (for example, by soaking into the ground after irrigation), Wurtsbaugh says the new calculations show that the overall amount fell 39% from 2003 to 2012. This, in addition to long-term stream records, suggests that climate change isn’t the culprit.

“This type of work is great to understand what’s changing and why,” says Hilary McMillan, a hydrologist at San Diego State University in California who was not involved with the study. She adds that the study “proves twice over” how much of the change is due to climate change versus human consumption—vitally important for helping water managers predict water needs. Conservation scientist Stephanie Januchowski-Hartley at Paul Sabatier University in Toulouse, France, agrees.She says that typically, policymakers report natural variations as the main reason for decreasing water. “From a policy perspective, this paper will have implications.”

Those policies could have an outsize impact on public health. As dry lakebed is exposed, salts and sediments can go airborne, causing respiratory and cardiovascular problems, says Maura Hahnenberger, an atmospheric scientist at Salt Lake Community College. She says that dust storms in Salt Lake City have typically blown in from distant lakebeds like the Bonneville Salt Flats, about 170 kilometers away. But as the Great Salt Lake declines, “the [pollution] source is very close to the population centers.”

Humans aren’t the only creatures affected. Saltwater lakes, which account for nearly a quarter of such water bodies around the world, create unique ecosystems for plants and animals like brine shrimp and the endangered peregrine falcon. They also provide habitats for migrating birds, many of which bulk up on brine shrimp before and during their long journeys.

Wurtsbaugh says that the key to preserving saltwater lakes (including Iran’s Lake Urmia) is to strike a balance between human consumption and conservation. The team concludes that inflows to the Great Salt Lake will need to increase 24% to 29% to maintain its health and stability. Wurtsbaugh adds that with the population of Utah set to double by 2050, long-term conservation and planning is crucial. “We need to be thinking 50, 100, 200 years out.”