Climate Change is Drying out Lakes Faster than Scientists Thought

By Dan Stillman / The Washington Post

16:19 JST, May 20, 2023

Water loss in large lakes around the world was more widespread during the past three decades than previously thought, according to a study of nearly 2,000 such lakes published in the journal Science on Thursday. A warming climate and human water consumption drove at least half of the decline in natural lakes, the study found. Reservoirs, or artificial lakes, also showed substantial drops.

The drying of lakes and reservoirs around the world is increasingly stressing water supplies for drinking and agriculture, endangering habitats for plants and fish, reducing the capacity to generate hydropower, and threatening marine recreation and tourism. The study said accurate tracking of lake water trends and identification of factors contributing to water loss can help guide water-management strategies affecting up to 2 billion people.

Record-low water levels in some of the world’s largest lakes have been well-documented in recent years, but the authors say previous studies have been limited by looking at only a small number of lakes or by gaps in lake water data. That resulted in an underestimation of the global drying trend and poor understanding of what’s driving it.

“Our findings suggest that drying trends worldwide are more extensive than previously thought, certainly with respect to lake volume and storage,” Fangfang Yao, the lead author of the study, said in an email. Differentiating between the human and natural contribution “helps us understand human alteration of the water cycle and also helps identify management solutions.”

The study found that 53 percent of the world’s largest lakes experienced significant declines from 1992 to 2020, with a global decline of 19 to 24 gigatons per year (a gigaton is a billion metric tons), equivalent to the total amount of water used in the United States in one year. The decline was found in both arid regions prone to drought and humid regions prone to heavy rainfall, both of which are expected to become more frequent and intense in a warming world.

Yao said that while previous studies suggested a “dry-get-drier and wet-get-wetter” pattern, he and his colleagues found that even in humid regions, “an intensified water cycle in a warming climate may not result in increased water storage” due in part to increased evaporation and potentially longer drought recovery times.

The study, which analyzed 1,972 lakes representing 95 percent of the world’s total volume of lake water, used 28 years’s worth of satellite observations to estimate lake water volume trends and a water model to quantify the separate contributions to water loss of natural variability, climate change and human water consumption.

“A thorough understanding of water supply drivers is critical to effectively managing reservoirs and river systems. The better we understand anthropogenic affects on our water supply, the better prepared we as water managers will be,” said Bart Leeflang, the Colorado River program manager for the Central Utah Water Conservancy District, who was not involved in the study. “We will face fewer crises, like we have been facing on the Colorado River over the last 20 years, and we will have resilient and reliable water supplies.”

Climate warming and human water consumption accounted for 47 percent to 65 percent of natural lake volume decline, the study found. In a further breakdown, about 36 percent of the decline is attributed to climate warming, which increases the amount of water evaporated into the atmosphere, while about 20 percent is attributed to human water consumption. Scientists have previously established that most climate warming since preindustrial times is due to human activities.

The study also analyzed water-level changes in reservoirs, or artificial lakes created by dams. It found a significant decline in almost two-thirds of them, largely because of sedimentation, which is the deposition of rock fragments, soil or dissolved material at the bottom of a body of water due to erosion. This reduces a body of water’s capacity, since these sediments take up space.

Yao said these reservoirs “will become less reliable for freshwater and hydroelectric energy supply” as additional sediment builds up as they age.

Many of the lakes in decline were in highly populated regions including the United States, Central Asia, the Middle East, western India, eastern China, northern and Eastern Europe, northern Canada, southern Africa, most of South America and Oceania, which includes Australia, New Zealand and Papua New Guinea. The 24 percent of large lakes that saw significant gains in water storage were largely in remote or underpopulated regions of the world.

In the United States along the Colorado River, both Lake Powell and Lake Mead, the nation’s two largest reservoirs, have dipped to dangerously low levels in recent years because of a historic drought that began in 2000 and years of water overuse. Utah’s Great Salt Lake has also seen a dramatic drop, losing more than 70 percent of its water since 1850; it reached a record low in November.

Water levels in all three lakes have been rising in recent weeks because of melting of this year’s record-setting snowpack in the West. That has allowed the U.S. Bureau of Reclamation to release extra water from Lake Powell into Lake Mead, which supplies water to about 25 million people in the Southwest. Experts say the relief is limited and temporary, though, with Lake Powell forecast to rise to only 30 percent of its capacity by this fall.

California, Arizona and Nevada are reportedly close to agreeing on a plan to conserve enough Colorado River water in the next three years to sustain water supply for drinking and farming, maintain hydroelectric power generation and avoid the ultimate catastrophe of “dead pool,” which occurs when a reservoir’s water level drops too low to flow downstream or generate electricity.

Understanding what factors are driving water loss is important for developing such water-management strategies, Yao said.

“For drying lakes dominated by overconsumption, effective water conservation efforts can help save these water bodies,” Yao said. “For drying lakes attributable to climate warming, climate mitigation [reducing greenhouse gas emissions] can help alleviate the more long-term impacts on these lake systems.”