Half of the world’s largest lakes and reservoirs are drying up

More than half of the largest lakes and reservoirs in the world are shrinking and endangering the water security of humanity, being the climate change and unsustainable consumption the main culprits, according to an academic study published on Thursday.

“Lakes are in danger all over the world, and this has large-scale implications,” Balaji Rajagopalan, a professor at the American University of Colorado Boulder and co-author of the study, published in the scientific journal Science, told AFP.

“It really struck us that 25% of the world’s population lives in a lake basin that is on a downward trend,” he continued, meaning some 2 billion people are affected by the findings.

Unlike rivers, which tend to hog scientific attention, lakes are not well monitored, despite their critical importance to water safety, Rajagopalan said.

However, environmental catastrophes in large bodies of water such as the sea Caspian and the sea de Aral signaled to investigators the existence of a larger crisis.

To study the issue systematically, the team, which included scientists from United States, France and Saudi Arabiaanalyzed the 1,972 largest lakes and reservoirs on Earth, using satellite observations between 1992 and 2020.

They focused on the larger freshwater bodies because of the higher precision of large-scale satellites, as well as their importance to humans and wildlife.

603 cubic kilometers less water

Their data set combined images from Landsat, the longest-running Earth-observing program, with the height of the water surface taken by satellite altimeters, to determine how the volume of the lakes varied over nearly 30 years.

The results: 53% of the lakes and reservoirs experienced a decrease in water storage, at a rate of approximately 22 gigatons per year.

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

To find out what caused these phenomena, the team used statistical models that incorporated climatic and hydrological trends and distinguished natural factors from those of human origin.

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

Increased temperatures caused by climate change favor evaporation, but may also reduce precipitation in some places.

“The climatic signal affects all factors”, Rajagopalan stated.

Lead author Fangfang Yao, a visiting professor at the University of California at Boulder, added in a statement: “Many of the human and climate change traces in lake water losses were unknown until now, such as the drying up of Lake Good-e-Zareh in Afghanistan and Lake Mar Chiquita in Argentina.”

Losses also in humid regions

One surprising aspect was that lakes in both wet and dry regions of the world are losing volume, suggesting that the paradigm of “The dry becomes drier, the wet more humid”, which is often used to summarize how climate change affects regions, is not always true.

Losses were detected in humid tropical lakes in the Amazon region, as well as in Arctic lakes, demonstrating a more widespread trend than expected.

Yet while most of the world’s lakes were shrinking, almost a quarter saw their water storage increase significantly.

This encompasses the Tibetan Plateau, “where the retreat of glaciers and the melting of permanently frozen soils partially promoted the expansion of alpine lakes”according to the study.

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

Is “unique because it focuses on specific lakes and reports the amount of water as a volume”said.

But added: “It is important to note that many water supplies come from small lakes and reservoirs” and future research should also consider them.

Globally, freshwater lakes and reservoirs store 87% of the planet’s liquid freshwater, underscoring the urgency of new strategies for sustainable consumption and climate change mitigation.

“If a good part of the freshwater lakes are drying up, the impact will come to you one way or another, if not now, it will be in the not too distant future,” concluded Rajagopalan.

Source: AFP