Lakes store 87% of the Earth's freshwater, making them a valuable resource for humans and terrestrial ecosystems. Unlike rivers, which are not well monitored, lakes provide water for a large percentage of humans, a percentage that even exceeds that of rivers.

However, according to a new study published in the journal Science on May 18 of this year,, more than 50 percent of the world's major lakes and water bodies are experiencing declines in water volume due to unsustainable human consumption and global warming.

The researchers devised a technique to monitor changes in water levels in nearly 2,000 of the world's large lakes and reservoirs - which account for 95 percent of the water stored in all lakes on Earth.

This innovative technique combines 30 years of satellite monitoring processes with models to track and interpret changes in lake storage on a global scale.



First assessment of its kind
The motivation for conducting this study lies in the environmental crisis that researchers have observed occurring in some of the largest waters on Earth, such as the drying up of the Aral Sea, located at the border of Kazakhstan and Uzbekistan.

As such, the team believes that this assessment is the first of its kind, based on a combination of satellites and models, to comprehensively assess trends in global lake water storage changes and their drivers.

The study's co-author, Balaji Rajagopalan, professor of hydrology and civil engineering at the University of Colorado in Boulder, USA, explained in a statement to Al Jazeera that prior to this study, the research community still lacked a clear understanding of long-term trends in water level changes, but now, based on the results produced by the team, "we are now able to use these findings and the methods underlying the research process to gain a broader perspective on the changes occurring in global lake levels.

To illustrate these trends in natural lakes, the team took advantage of recent advances in water use and climate modeling. They concluded that climate change and human water use are the main causes of the net decrease in the area of natural lakes worldwide and the loss of water from nearly 100 large lakes.

Rajagopalan noted that to reach these conclusions presented in the study, the team used nearly 250,000 images of lake areas taken by satellite between 1992 and 2020 to survey the area of the world's largest 1,972 lakes. Thereafter, the team combined recent water level measurements with area measurements of the region over a long period of time to reconstruct lake volumes from decades ago.


Globally, lakes are shrinking in size in both arid and wet areas (social networking site)
Worrying results
The study's co-authors note, "In fact, the results from our study are worrying. About 53 percent of the world's lakes are losing water storage. This water loss is 17 times the amount of water stored in Lake Mead, the largest reservoir in the United States."

The researchers noted that globally, the size of lakes is shrinking in both arid and wet regions, and that this loss of water, which is occurring in the humid tropics as well as in Arctic lakes, indicates that the drought trend is more widespread than previously perceived.

According to a press statement posted on the EurekAlert website, in addition to studying natural lakes, the team also looked at trends in water storage in reservoirs and found that about two-thirds of the planet's large reservoirs are experiencing significant water loss.

According to the study, sedimentation processes are one of the reasons for the current global decline in reservoir storage - the rise of lake bottoms due to the accumulation of muddy or sandy sediments. The study also found that sedimentation processes have had a greater impact than drought for reservoirs created before 1992.

However, not all lakes are shrinking - this study shows that 24 percent of the world's lakes are showing a significant increase in water storage.

These lakes are mainly located in sparsely populated areas, such as the interior of the Tibetan Plateau, the northern Great Plains of North America, and in areas with new reservoirs, such as the Yangtze, Mekong, and Nile river basins.

The authors of this study estimate that nearly 2 billion people (about a quarter of the world's population) live within these threatened or dried-up lake basins.

These statistics will provide further impetus to consider the impact of human consumption, climate change and sedimentation processes on water management strategies.