Half Of World's Lakes And Reservoirs Drying Up, Says Study

Over half of the world's lakes and reservoirs are drying up and putting humanity's water security at risk, with climate change and unsustainable consumption the main culprits, a study said on Thursday.

Balaji Rajagopalan, a professor at the University of Colorado Boulder and co-author of the study, told AFP that lakes are in trouble globally, which has far-reaching implications. According to him, 25% of the world's population is living in a lake basin that is on a declining trend.

Unlike rivers, lakes aren't well-monitored, despite being crucial for water security, he said. High-profile environmental disasters in large water bodies, such as the Aral and Caspian Seas, signalled a wider crisis to researchers.

Comprised of scientists from the US, France, and Saudi Arabia, the team looked at Earth's biggest 1,972 lakes and reservoirs, using observations from satellites from 1992-2020.

Their focus was on larger freshwater bodies because of the better accuracy of satellites at a larger scale and their importance for humans and wildlife.

The researchers' database merged images from Landsat, with water surface height acquired by satellite altimeters, to determine how lake volume varied over nearly three decades.

The results showed that 53% of lakes and reservoirs witnessed a decline in water storage at a rate of approximately 22 gigatonnes per year.

Climate Warming & Decline In Water Storage

Over the entire period studied, 603 cubic kilometres of water was lost, 17 times the water in Lake Mead, the largest reservoir in the United States.To discover what drove the trends, the researchers used statistical models incorporating hydrologic and climate trends to tease out natural and human-driven factors.

As for natural lakes, most of the loss was attributed to climate warming and human water consumption.Rise in temperatures from climate change results in evaporation but can also decrease precipitation in some places.

Lead author Fangfang Yao said many human and climate change footprints on lake water losses were previously unknown.

One surprising aspect was that lakes in both dry and wet regions are losing volume. Losses were found in humid tropical lakes in the Amazon and Arctic lakes, demonstrating a trend more widespread than predicted. Accumulation of sedimentation was blamed for storage loss in drying reservoirs.

Although most global lakes were drying, nearly a quarter witnessed a significant rise in their water storage.

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

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