Highlights: More than half of the world's largest lakes have declined over the past three decades. Main causes of the decline in water reserves: human activity, but also climate change, including the lack of precipitation and rising temperatures that accelerate the evaporation of resources. The drying up of natural lakes or reservoirs is all the more worrying because they represent 87% of the liquid fresh water available on earth. "Clearly, the footprint of climate change is already there," says the researcher who led the study.

According to a study published Thursday, May 18 in the prestigious journal Sciences, more than half of the world's lakes are emptying because of climate change and human activity. This alarming finding...

Environment: half of the world's lakes and reservoirs in sharp decline in water

A boat docks on a completely dry stretch of Lake Alhajuela, in Colon province, 50 kilometers from Panama City, April 21, 2023. © Luis Acosta / AFP

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According to a study published Thursday, May 18 in the prestigious journal Sciences, more than half of the world's lakes are emptying because of climate change and human activity. This alarming finding highlights the threat to a vital source of freshwater.

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The bottom of Lake Titicaca in Bolivia is dry. In France, the alpine lake of Serre-Ponçon now reveals new banks, ditto for the lake of Vouglans, in the Jura. The drying up of natural lakes or reservoirs is all the more worrying because, even if these water reserves cover only 3% of the surface of the globe, they represent 87% of the liquid fresh water available on earth.

In total, a quarter of the world's population has settled around a lake or reservoir that is now drying up, reveals the study, which also carries an interactive map. Initially, with the aim of better exploiting them for human consumption, agriculture or electricity production.

More than half of the world's largest lakes have declined over the past three decades.

Nearly one-quarter of the world's population resides in a basin with a drying lake, which underscores the importance of management solutions. Learn more in Science: https://t.co/Z3Nb6rFqDu pic.twitter.com/T3scUHC4KJ

— Science Magazine (@ScienceMagazine) May 18, 2023

Main causes of the decline in water reserves: human activity, but also climate change, including the lack of precipitation and rising temperatures that accelerate the evaporation of resources.

Previous work has already looked at the decline of larger lakes individually. But this study is the first to offer a detailed view of global trends, and the causes of the observed changes, thanks to satellite observations.

In total, the researchers studied 1,972 bodies of water, representing the vast majority of natural lakes (focusing on those larger than 100 km2) and reservoirs. Over the almost 30-year period studied (from 1992 to 2020), the study concludes that they were emptied of the equivalent of all water consumption in the United States in 2015.

A graph on the evolution of the volume of water in lakes across the globe, according to a study published in the journal Science on May 18, 2023. © Science review

« The footprint of climate change is already there »

What worries researchers who warn about the snowball effect of the drying up of lakes. Indeed, when they disappear, they can no longer exercise their role of carbon storage, which also accelerates global warming. Like the oceans, lakes also store carbon, and no longer play this role when they disappear, in turn aggravating global warming.

The study has an unexpected result: lakes lose water not only in drylands, but also in humid regions. "It is generally considered that when the climate warms, arid regions dry out even more, and humid regions become wetter," says Rajagopalan. But even in the latter, "the lakes are declining", which is "surprising", he stressed, giving the example of India.

For natural lakes, they attribute about half of water losses to human activities and rising temperatures, which cause increased evaporation – the latter factor being linked to climate change.

But another important factor, the lack of rainfall, "can also be attributed to climate change in some places," Rajagopalan said. In addition, humans or herds may have to consume more water because of higher temperatures. "Clearly, the footprint of climate change is already there," says the researcher.

The two graphs on the volume of water in lakes across the globe show that the number of water reservoirs that have decreased in volume is much greater than those that have seen an increase, according to a study published in the journal Science on May 18, 2023. © Science review

« It's not too late to intervene »

The researchers' message is not fatalistic: on the contrary, they seek to raise awareness. Faced with such an observation, scientists encourage people to change their uses and better manage their water consumption.

For some lakes, "it's not too late to intervene," says Rajagopalan. Policymakers are now "armed with information".

The authors of the study call for more control and monitoring, especially smaller lakes receiving less attention, and for management at the regional level, considering several lakes at the same time, on the model of river management by several jurisdictions at the same time.

Finally, they stress the importance of preventive measures, such as transferring to another water source if the threshold of a lake reaches a critical level.

► " READ ALSO – Groundwater and drought in France: seven questions to understand

Environment: half of the world's lakes and reservoirs in sharp decline in water

Environment: half of the world's lakes and reservoirs in sharp decline in water

« The footprint of climate change is already there »

« It's not too late to intervene »

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