More than 50% of the world’s largest lakes are losing water

53% of the world’s largest lakes are in decline and store less water than they did three decades ago, according to a study published today by the journal Science. These natural reservoirs contain 87% of the Earth’s surface liquid fresh water. Furthermore, they provide essential ecosystem services and are a key component of global biogeochemical processes.

According to the authors, led by the CIRES institute at the University of Colorado at Boulder (USA), this decrease is mainly due to climate change -due to increased temperatures and reduced flows that cause evaporation-, human consumption and sedimentation in reservoirs.

53% of the world’s largest lakes are in decline and hold less water than three decades ago

“This is a kind of ‘progressive disaster’ as it occurs over years and decades. The result of sedimentation, for example, will be that reservoirs will be able to store less, making them less reliable for supplying fresh water and hydroelectric power, especially in countries with quite old reservoirs,” said Fangfang Yao, researcher, to SINC .Visitor of CIRES, currently at the University of Virginia (USA).

Sediment flushing can aid in its removal. Reservoir sedimentation rates accelerate with climate change, due to increased extreme rainfall, as well as land disturbances such as wildfires, landslides or deforestation. “If we take measures on these aspects, we can mitigate the impact of climate change on the reservoirs”, argues the scientist, who was motivated to carry out this research due to the drying up of the Aral Sea between Kazakhstan and Uzbekistan.

Innovative technology and interactive map

The study focused on water storage in lakes and reservoirs with data from nine different satellites, using an innovative technique to reconstruct past water storage data. With this new methodology, the authors intend to give water resource managers and communities an idea of ​​how best to protect these water sources, which are essential for regional ecosystems. Furthermore, they provide a interactive map with global lake water storage trends and drivers.

Among the bodies of water studied there are 17 peninsular lagoons, 13 of them in Spanish territory. “Approximately half (between 40% and 60%) of the large lakes on the Iberian Peninsula were losing water. In general, Western European lakes are in decline. But two recently filled reservoirs, the Baixo Sabor and Alqueva lakes in Portugal, show an increase in water storage. Lake Alarcón, in Spain, also shows an increase in water storage”, points out the researcher.

About half (between 40% and 60%) of the large lakes on the Iberian Peninsula were losing water

Fangfang Yao (CIRES)

The results of the work highlight the importance of taking these effects into account in future surface water resources management strategies. Direct human activities such as dam building and water consumption, as well as ongoing climate change, increasingly threaten these essential water resources.

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Human activities such as dam construction and water consumption, along with climate change, threaten these essential water resources.

“You have to be careful with the use of water in dry years. If farmers worry too much about crop failure and use too much water for irrigation, it can increase drought and cause low levels in downstream lakes.

Raising awareness and informing about water use will help prevent environmental disasters in lakes during dry years,” continues Yao.

Huge amount of satellite images

For the new work, the team used 250,000 photos of the lake area taken by satellites between 1992 and 2020 to study the surface of 1,972 of the largest lakes on Earth. They collected water levels with nine satellite altimeters and used long-term water data to reduce any uncertainty.

To carry out the research, 250,000 snapshots of the lake area captured by satellites between 1992 and 2020 were used.

For lakes without long-term records, they used water measurements taken with newer instruments on satellites. Combining level measurements with long-term surface indicators is what allowed them to reconstruct the volume of lakes decades ago.

“Water loss from lakes is prevalent in major regions of the world such as West Central Asia, Middle East, West India, East China, North and East Europe, Oceania, United States, North Canada, South Africa and most of part of South America. ”, says the expert.

Water loss also in reservoirs

Yao and his team also looked at storage trends in reservoirs. And they found that nearly two-thirds of the largest experienced significant water losses.

“Sedimentation dominated the overall decline in storage in existing reservoirs,” says Ben Livneh, another member of CIRES.

While most of the world’s lakes are shrinking, 24% have experienced significant increases in water storage. Those that are growing tend to be in sparsely populated areas in the interior of the Tibetan Plateau and the Great Plains of North America, as well as in areas with new reservoirs such as the Yangtze, Mekong and Nile river basins.

A quarter of the world’s population, 2 billion people, live in a lake basin that is drying up.

The authors estimate that about a quarter of the world’s population, 2 billion people, reside in a dry lake basin, indicating an urgent need for sustainable management of water resources.

“If human consumption is an important factor in the decline of water storage in the lake, we can adapt and explore new policies to reduce large-scale depletion,” concludes Livneh.

Reference:

Fangfang Yao and others. “Satellites reveal widespread decline in global water storage in lakes”. Science2023

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