More than half of the world's major lakes and dams have experienced significant water reductions over the course of over the last 30 years, as revealed by a recent study released by the journal Science on Thursday (18).
This situation is largely attributed to climate change and the overexploitation of water resources.
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The research also points out that approximately a quarter of the global population resides in areas affected by droughts in lake beds.
Although lakes cover only about 3% of the planet's surface, they hold nearly 90% of the world's liquid fresh water supply.
Consequently, these water bodies play an essential role as sources of drinking water, irrigation and power generation, as well as providing crucial habitats for animals and plants.
More details on what's happening to the world's largest lakes
Water level fluctuations in lakes are influenced by natural climatic variations, especially rainfall and snowfall.
However, even these natural phenomena are being increasingly impacted by human activities.
On a global scale, major lakes have experienced a significant drop in water levels.
An example of this is Lake Mead, located on the Colorado River in the southwestern United States, which has its lowest level in decades.
The Caspian Sea, which stretches between Asia and Europe and is considered the largest continental water reserve in the world, has been shrinking over time due to climate change and water consumption.
Fangfang Yao, climatologist responsible for the study, points out that the reduction in water levels in the large lakes has been observed for years, however, until now, no study had investigated this phenomenon in a comprehensive way. embracing.
"The shrinkage of many lakes has been well documented, but the extent of the change - and the reasons behind it - have been examined less closely," Yao said.
The study methodology
By analyzing more than 250,000 satellite imagery records between 1992 and 2020, combined with climate models, the researchers in charge of this new study managed to reconstruct the trajectory of the lakes from decades ago.
The results revealed that 53% of the lakes and reservoirs suffered significant water losses, amounting to a net loss of approximately 22 billion tons annually.
To illustrate the magnitude of this volume, the scientists compared the amount to the equivalent of 17 Lake Meads.
Furthermore, the report highlighted that the reduction in water storage occurred in lakes in all regions of the globe, including the tropics and the Arctic.
These data alert to the scope of the problem, as Fangfang Yao points out, indicating that drying trends worldwide are broader than previously assumed.
More and more lakes affected by drying
Two other huge lakes affected by the drying process are the Aral Sea in Uzbekistan and the of Salton, California, USA, as well as the Great Salt Lake, located in Utah, another state North American.
In these three cases, the scientists identified a strong correlation between the exorbitant demand for water and the phenomenon of the reduction of lakes, since they are all located close to large centers urban.
According to the study, as the lakes decrease in size, the acidity of the surrounding watersheds increases, which in turn intensifies evaporation and accelerates their decline.
In lakes located in colder regions of the world, winter evaporation becomes an increasing challenge, because the higher temperatures cause the ice that usually covers them to melt, exposing the water to atmosphere.
In Arctic lakes, for example, the decline is related to a combination of changes in temperature, precipitation, evaporation and runoff.
These transformations can trigger chain effects, including a deterioration in water quality, an increase in toxic algal blooms, and an increase in the loss of aquatic life.
“An important aspect that is often not recognized is the degradation of lake water quality due to a warmer climate, which decreases the water supply for the communities that depend on them,” said FangFang Yao.
Water reservoirs are also shrinking
In the case of reservoirs, according to the report, the main cause for the decline is sediment deposition. These sediments are carried into the water, clogging it and reducing its available space.
An example of this is Lake Powell, the second largest freshwater reservoir in the United States, which suffered a decrease of almost 7% in its storage capacity due to the accumulation of sediments.
Sedimentation can be influenced by climate change, wildfires and other problems that intensify as the planet warms.
There is still hope
Despite the worrying data, the study highlights that not all of the world's major lakes are experiencing declines in their water levels.
On the contrary, approximately one-third of the reductions in lake water levels were offset by increases in other regions. As a result, some lakes have seen growth, with an average increase of 24% in their water storage.
These expanding lakes are located primarily in less densely populated areas, including regions in the Northern Great Plains of North America and in the interior of the Tibetan Plateau.
Climate change also plays a role in this increase in volume in certain lakes, as melting glaciers contribute to the increase in water in their basins.
FangFang Yao also emphasized the importance of adopting a conscientious management of water resources, highlighting the need to act responsibly towards fresh water.
“As many parts of the world become hotter and drier, lakes must be managed properly. Otherwise, climate change and human activities could lead to their drying up sooner than we think.”
