() — More than half of the world’s largest lakes and reservoirs have lost significant amounts of water in the past three decades, according to a new study, which largely blames climate change and excessive water use.
Approximately a quarter of the world’s population lives in the basin of a lake that is drying up, according to a study by an international team of scientists, published Thursday in the journal Science.
Although lakes only cover about 3% of the planet, they contain almost 90% of its fresh surface liquid water and are essential sources of drinking water, irrigation and energy, as well as providing vital habitats for animals and plants.
But they have problems.
Lake water levels fluctuate in response to natural weather variations of rain and snow, but are increasingly affected by human action.
Around the world, major lakes are experiencing sharp declines. The Colorado River’s Lake Mead in the southwestern US has receded dramatically amid a megadrought and decades of overdrafting. The Caspian Sea, between Asia and Europe, the world’s largest inland body of water, has been shrinking for some time due to climate change and water use.
The decline in the size of many lakes is well documented, but the extent of the change and the reasons for it have not been as thoroughly examined, says Fangfang Yao, the study’s lead author and a visiting professor at the Cooperative Research Institute for Environmental Sciences at the University of Colorado at Boulder.
The Caspian Sea is receding rapidly due to climate change and human activity. Credit: NASA
The researchers used satellite measurements of nearly 2,000 of the world’s largest lakes and reservoirs, which together account for 95% of Earth’s total lake water storage.
By examining more than 250,000 satellite images spanning from 1992 to 2020, along with climate models, they were able to piece together the history of the lakes going back decades.
The results were “shocking,” according to the report’s authors.
They found that 53% of lakes and reservoirs had lost significant amounts of water, with a net decrease of about 22 billion metric tons a year, an amount the report authors compared to 17 times the volume of Lake Mead.
According to the report, more than half of the net loss of water volume in natural lakes can be attributed to human activities and climate change.
A boat submerged on the dry bed of Lake Mead on June 14, 2022. Credit: Roger Kisby/The Washington Post/Getty Images
The report found losses in lake water storage everywhere, including in the humid tropics and the cold Arctic. This suggests that “worldwide desiccation trends are broader than previously thought,” Yao said.
Different lakes have been affected by different causes.
According to the report, unsustainable water use is the predominant reason for the wilting of Uzbekistan’s Aral Sea and California’s Salton Sea, while changes in rainfall and runoff have fueled the decline of Utah’s Great Salt Lake.
In the Arctic, lakes have been shrinking due to a combination of changes in temperature, precipitation, evaporation, and runoff.
“Many of the human and climate change traces of lake water losses were unknown until now,” Yao said, “such as the drying up of Lake Good-e-Zareh in Afghanistan and Mar Chiquita in Argentina.”
Dust rising from the Chiquita sea, Argentina, in July 2022. Water levels are now consistently lower than they were in the 1980s and 1990s, due to drought and water withdrawals. Credit: NASA
Climate change can have various impacts on lakes. The most obvious, according to Yao, is increased evaporation.
According to the study, shrinking lakes may contribute to the “aridification” of the surrounding basin, which in turn increases evaporation and accelerates its decline.
In lakes in the coldest parts of the world, winter evaporation is an increasing problem, as warmer temperatures melt the ice that usually covers them, exposing the water to the atmosphere.
These changes can have cascading effects, including decreased water quality, increased toxic algae blooms, and loss of aquatic life.
“An important aspect that is often unrecognized is the degradation of lake water quality due to warmer weather, which places a strain on the water supply of the communities that depend on them,” Yao explained.
The exposed bed of the Aral Sea on May 5, 2018 near Muynak, Uzbekistan, which used to be the fourth largest lake in the world. Credit: The Asahi Shimbun/Getty Images
In the case of reservoirs, the report finds that the main factor behind their decline is sedimentation, which causes sediment to flow into the water, clogging it and reducing its space. This is a “progressive disaster,” Yao explains, occurring over years and decades.
Lake Powell, for example, the second largest man-made reservoir in the United States, has lost nearly 7% of its storage capacity due to sediment buildup.
Sedimentation may be affected by climate change, he added. Forest fires, for example, growing more intense as the world warms, burn forests and destabilize the soil, contributing to increased sediment flow into lakes and reservoirs.
“The result of siltation will be that reservoirs will be able to store less water, making them less reliable for supplying fresh water and hydroelectric power, especially for us here in the US since our nation’s reservoirs are quite old,” says Yao.
According to the report, not all lakes are declining, as about a third of the declines are offset by increases elsewhere.
Some lakes have grown, with a 24% significant increase in water storage. According to the report, these are usually lakes located in less populated regions, such as the Great Plains of North America and the interior of the Tibetan plateau.
The traces of climate change are present in some of these rises, as melting glaciers fill the lakes, posing a potential risk to people living downstream.
As for reservoirs, while nearly two-thirds experienced significant water loss, overall there was a net increase as more than 180 reservoirs recently filled, according to the report.
Catherine O’Reilly, a professor of geology at Illinois State University, who was not involved in the study, said this new research provides a useful set of long-term data that helps tease out the relative importance of the factors driving the decline. of the lakes
“This study highlights the impact of climate in a very close way: how much water do we have access to and what are the options to increase its storage?” he told .
“It’s a bit scary to see how many freshwater systems are unable to store as much water as before,” he added.
As many parts of the world become hotter and drier, lakes need to be managed properly.
Otherwise, climate change and human activities “may cause them to dry out sooner than we think,” Yao said.
