Over half of world’s largest lakes dwindle, threatening water security

A recent study has revealed that over half of the world’s largest lakes and reservoirs are shrinking, jeopardising global water security’s future. Climate change and unsustainable consumption have been identified as the primary causes of this alarming trend.

“Lakes are in trouble globally, and it has implications far and wide,” said Balaji Rajagopalan, a professor at the University of Colorado Boulder and co-author of the paper, which was published in Science. He also noted that around two billion people, or 25% of the world’s population, live in lake basins that are experiencing a decline in water levels.

Lakes have not been as closely monitored as rivers, despite their critical importance for water security. However, high-profile environmental disasters in large water bodies like the Caspian Sea and the Aral Sea have prompted researchers to investigate the issue further. The study involved scientists from the United States, France, and Saudi Arabia, who examined the Earth’s 1,972 largest lakes and reservoirs using satellite observations from 1992 to 2020.

The results were concerning. 53% of lakes and reservoirs experienced a decline in water storage, at a rate of about 22 gigatonnes per year. Over the entire period, 603 cubic kilometres of water were lost, which is equivalent to 17 times the amount of water in Lake Mead, the United States’ largest reservoir, reported Bangkok Post.

To determine the causes behind these trends, the researchers used statistical models that incorporated climate and hydrologic trends. They found that climate warming and human water consumption were major factors contributing to the net loss of water in natural lakes.

“The climate signal pervades all factors,” Rajagopalan said. Lead author Fangfang Yao, a visiting fellow at the University of Colorado Boulder, added: “Many of the human and climate change footprints on lake water losses were previously unknown, such as the desiccations of Lake Good-e-Zareh in Afghanistan and Lake Mar Chiquita in Argentina.”

Interestingly, the study found that lakes in both wet and dry regions of the world are losing volume. This challenges the commonly held belief that climate change causes dry areas to become drier and moist areas to become wetter. Losses were discovered in humid tropical lakes in the Amazon as well as Arctic lakes, indicating a more widespread trend than previously anticipated.

While the majority of global lakes are shrinking, nearly a quarter of them have experienced significant increases in water storage. Some of these lakes are located in the Tibetan Plateau, where glacier retreat and permafrost thawing have driven alpine lake expansion.

Hilary Dugan, a scientist who studied freshwater systems at the University of Wisconsin-Madison and was not involved in the study, praised the research for advancing scientific understanding of lake volume variability. “It is unique in that it focuses on specific lakes, and reports the amount of water as a volume,” she said. However, she also pointed out that many water supplies come from smaller lakes and reservoirs, which should be considered in future research.

With freshwater lakes and reservoirs storing 87% of the Earth’s liquid freshwater, the study highlights the urgent need for new strategies to promote sustainable consumption and climate mitigation. “If a good chunk of freshwater lakes are drying, then you’re going to see the impact come to you one way or the other, if not now in the not-too-distant future,” Rajagopalan warned. “So it behoves all of us to be good stewards.”