More than half of the world’s lakes are drying up, says study – 05/18/2023 – Environment

More than half of the world’s largest lakes and reservoirs are drying up, putting humanity’s water future at risk, says a study published this Thursday (18), which points to unsustainable consumption and climate change as the main culprits.

“Lakes are in trouble around the world and this has implications everywhere,” Balaji Rajagopalan, a professor at the University of Colorado at Boulder, in the United States, and co-author of the research, published in the journal Science, told AFP.

“It really caught our attention that 25% of the world’s population lives in a lacunar basin that is on a declining trend,” he added, meaning that around two billion people are impacted by these discoveries.

Unlike rivers, which tend to monopolize scientists’ attention, lakes are not well monitored despite their critical importance to water security, Rajagopalan said.

But large-scale environmental disasters in vast bodies of water like the Caspian and Aral Seas have shown scientists a broader crisis.

To systematically track the issue, the team of researchers, which includes scientists from the United States, France and Saudi Arabia, observed the Earth’s 1,972 largest lakes and reservoirs, using satellite data from 1992 to 2020.

They focused on vast bodies of freshwater because of the greater accuracy of satellites for recording larger scales, and also because of their importance to humans and wildlife.

‘Climate permeates all factors’

Its database gathered Landsat images, the oldest active Earth observation program, with information on the height of the water surface, obtained by satellite altimeters, to determine how the lacunar volume varied over almost 30 years.

The result was that 53% of lakes and reservoirs are experiencing a decline in water storage at a rate of approximately 22 gigatons per year.

Over the period studied, 603 cubic kilometers of water were lost, 17 times the volume of water in Lake Mead, the largest reservoir in the United States.

To uncover the causes of this loss, the team of researchers used statistical models incorporating climatological and hydrological trends to identify natural and man-made factors.

In the case of natural lakes, much of the net loss was attributed to both global warming and human water consumption.

Higher temperatures brought on by global warming led to evaporation, but may also have decreased precipitation in some places.

“The weather signal permeates all factors,” said Rajagopalan.

Fangfang Yao, lead author of the study and visiting fellow at the University of Colorado, added in a note: “Many of the human and climate change impacts on water loss from lakes were previously known, such as the desiccation of Lake Good-e-Zareh, in Afghanistan, and the Mar Chiquita, in Argentina”, which despite its name is a lake in Córdoba (central-north).

Losses also in humid regions

One surprising aspect was that both lakes in dry and wet regions are losing volume, suggesting that the “dry gets drier, wet gets wetter” paradigm, often used to summarize how climate change affects regions, does not always hold true. keeps.

Losses were recorded in both humid tropical lakes in the Amazon and in the Arctic, demonstrating a more widespread trend than anticipated.

In addition, the loss of storage in reservoirs in the drying process was identified as responsible for the accumulation of sediments.

But while most of the world’s large lakes are drying up, nearly a quarter have seen a significant increase in their water storage.

Among them is the Tibetan Plateau, “where retreating glaciers and melting permafrost were partly responsible for the expansion of the alpine lake,” the article noted.

Hilary Dugan, a scientist who studies freshwater systems at the University of Wisconsin at Madison and who was not involved in the study, told AFP that the research advanced scientific understanding of lacunar volume variability, which is “of paramount importance”.

It is “unique in that it focuses on specific lakes and records the amount of water as volume,” he said.
But he also pondered: “It’s important to keep in mind that many sources of water supply are lakes and small reservoirs” and that new research needs to consider them as well.

Globally, lakes and reservoirs store 87% of the planet’s fresh water, which reinforces the urgency of adopting new strategies for sustainable consumption and the mitigation of climate change.

“If most freshwater lakes are dying, then we’re going to see the impact come one way or another, if not now then in the not-too-distant future,” Rajagopalan said. “So it’s up to all of us to be good stewards.”