More than 50% of the world’s largest freshwater lakes are storing less water annually, according to researchers at the University of Colorado Boulder, and human activity is cited as the key cause of the global net decline.

For a new study reported in Science, researchers from CU Boulder’s Cooperative Institute for Research in Environmental Sciences, Kansas State University, France and Saudi Arabia surveyed 250,000 satellite snapshots of Earth’s largest lakes between 1992-2020.

Out of 1,972 lakes surveyed, 53% showed a decline in water storage over the three-decade period.

“This is the first comprehensive assessment of trends and drivers of global lake water storage variability based on an array of satellites and models,” said Fangfang Yao, lead author and visiting fellow for CIRES, in a news release.

Researchers found that the global net lake water storage loss accumulated to 17 times the United States’ largest reservoir, Lake Mead. While arid regions proved to more commonly and more drastically experience drying trends, humid regions showed water decline that was more extensive than previous studies found.

Direct and indirect human activity accounted for most of the global lake volume decline. Over-consumption of drinking water and hydroelectricity and rising temperatures elevating evapotranspiration put humans and climate change at the forefront of the issue.

“I think some implications for management of water bodies, as the climate becomes more arid, it is crucial that lakes integrate other resources,” Yao said. “Arid bodies are particularly vulnerable to warmer temperatures.”

The study estimates that 2 billion people, roughly a quarter of the 2023 global population, live in basins where these lakes are experiencing significant declines.

“A quarter of the global population is receiving water from drying lakes; this highlights the importance of improvements in water management,” Yao said.

These lakes account for 87% of Earth’s liquid surface fresh water. The survey provides water managers with data on global trends to begin water conservation efforts.

“On a global scale, you need reliable estimates of lake levels and volume,” said co-author and CIRES fellow Balaji Rajagopalan. “With this novel method…we are able to provide insights into global lake level changes with a broader perspective.”

In the future, Yao says that researchers can repeat this survey’s methodology using satellite typography to maintain a database of lake water storage levels.

In March, the National Aeronautics and Space Administration began to receive images from the new international Surface Water and Ocean Topography mission. According to Yao, surveys of global water volume will be able to get much more localized for conservation planning with these new images.

“Surface Water and Ocean Topography, that satellite can provide images to repeat the methodology not only for big lakes but also small lakes that are important locally,” Yao said. “So that’s one success from this study.”