Global study of lakes enhances understanding of hydrological cycle

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Courtesy of Fluence Corporation

We now have much more robust data available on the amount of water in lakes worldwide thanks to a comprehensive database created by researchers at McGill University in Montreal.

The McGill scientists discovered the total shoreline of the world’s lakes is more than four times longer than the global ocean coastline. At 7 million kilometers, this is 10 times the distance from the Earth to the moon and back. If all the water in the world’s lakes were evenly spread over the Earth’s landmass, it would be roughly 4 feet deep.

There have been significant gaps and inconsistencies in the available global data, which is based on either lake surface area or shoreline length. Mapmakers may use varying resolutions and scales. Some small lakes are not mapped, and those spanning national borders may not be fully shown. Estimating the amount of water stored beneath a lake’s surface is even more difficult.

Satellite Measurement

The researchers used improved satellite data to obtain precise measurements of land surface elevation. They used existing lake-depth records — actual measurements of 12,000 lakes — and land elevation data, then extrapolated the calculations to all unmeasured lakes on Earth to estimate the depth of these lakes. They determined that the volume of water stored in more than 1.42 million lakes larger than 10 hectares (about 120,000 square yards) is more than 180,000 cubic kilometers. The project of making these calculations took three years.

The world’s 10 largest lakes contain roughly 85 percent of the total amount of water in lakes on Earth. The remaining 15 percent is found in more than 1.4 million lakes. Roughly two-thirds of the world’s lakes are in Canada.

Lakes and the Global Environment

This body of work should help other scientists better understand the role of lakes in the hydrological cycle as well as how they influence weather patterns and transport, and the distribution and storage of pollutants and nutrients.

Bernhard Lehner, an associate professor in McGill’s geography department and a senior author of the publication, explained:

Lakes are changing, in a changing world. […] Some are disappearing as there is less water to keep them filled, others are created or growing in regions where there is more rainfall. So we need a good inventory of the current status of lakes to understand and monitor their changes and the effects that this may have for our global environment.

The researchers said they were able to calculate the amount of time water typically “resides” in each of the lakes. On average, it’s about five years from the time water enters a lake until it flows out. For some lakes, it’s much shorter, while about 3,000 lakes have residence times estimated at 100 years or more, according to the scientists.

Mathis Messager, the study’s first author, who worked on the project as an undergraduate student in Lehner’s lab, said:

When you think of all the processes that take place at the interface of lakes and their landscapes, from providing habitat for aquatic or amphibian species to contributions to greenhouse-gas emissions, it underscores the importance of lakes in the Earth’s ecosystems.

Research Important for other Scientists

In addition to providing scientists with a current assessment of the world’s lakes and the water they contain, the data will also help climate-change researchers both forecast and assess changes over time.

Lehner adds that it is not only water scientists who are making use of the water mapping data. He told the Montreal Gazette:

I get unexpected requests. […] epidemiologists studying the global spread of water- and vector-borne diseases such as malaria; (archeologists) studying ancient travel or trade routes along water courses; (and) museums for exhibits that simply showcase the evolution of mapmaking.

The HYRDOLakes database can be accessed online. The McGill researchers say they are working to add new features, such as data on the surrounding watersheds that flow into these the lakes.

The findings — “Estimating the volume and age of water stored in global lakes using a geo-statistical approach” — were published in the journal Nature Communications.

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