Lakes are small in terms of Earth’s land surface but are key sites for biogeochemical activity. They significantly contribute to atmospheric carbon dioxide and methane levels, influencing the global carbon cycle.
Counting the number of lakes in the world until recently was more of a guessing game than an exact science. Accurately estimating the number and size of lakes worldwide has been difficult due to incomplete or inaccurate data. This has limited understanding of their role in global carbon cycles.
Traditional Methods for Counting Lakes
Current lake estimates rely on map compilations and statistical models. While map databases like the Global Lake and Wetland Database (GLWD) include large lakes, they often miss smaller ones. To fill this gap, statistical models extrapolate data to estimate the number of small lakes, but these models can be error-prone and overestimate lake numbers.
Advanced technology for counting the number of lakes
A recently study published in Geophysical Research Letters used satellite data to remotely sense the number of lakes larger than 0.002 square kilometers.
An automated algorithm called GWEM (GeoCoverTM Water bodies Extraction Method) was used on cloud-free Landsat satellite imagery to extract information about the number and size of lakes around the world, excluding the world’s largest inland water body, the Caspian sea, Antarctica, and the glaciated areas of Greenland.
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Researchers found that there are 117 million lakes larger than 0.002 km2 in the world which collectively cover 3.7% of Earth’s nonglaciated land area. The results of the study were used to create the GLObal WAter BOdies database (GLOWABO).
Previous estimates and inaccuracies for counting the number of lakes in the world
Previous counts extrapolated the number of the lakes based on computer models that have turned out to be inaccurate. In 2006, a study used a global model based on the Pareto distribution to estimate that there are 304 million lakes covering 4.2 million km2 in area, a calculation that turned out to grossly overestimate the number of lakes.
Geographic Distribution of Lakes
In the region between 60°N and 56°S, where elevation data is available, there are over 22 million water bodies larger than 0.01 km². Together, these water bodies cover 1.4 percent of the world’s non-glaciated land surface.
There are around 5 million lakes in an area with a greater lake surface area north of 60°N or south of 56°S. The latitudes of the boreal and arctic regions (45°-75°N) have the highest density of lakes (Figures a, c, and e in the graph below from the research).
Elevation also affects the size and abundance of lakes, with 85% of lakes, 50% of the total lake area, and 50% of the total lake perimeter located at elevations below 500 meters above sea level (Figures b, d, and f).
Key findings about the world’s lakes
- Number of lakes: About 117 million lakes.
- Total surface area of lakes: Approximately 5 million square kilometers, covering 3.7% of the Earth’s non-glaciated land.
- Dominant lake sizes: Large and medium-sized lakes make up most of the total lake surface area.
- Comparison with previous estimates: GLOWABO reveals fewer lakes than earlier models but a larger total surface area.
Advancements in limnology
The GLOWABO database significantly improves the accuracy of global lake counts and size distribution, providing essential data for environmental scientists studying the impact of lakes on global carbon cycles and other biogeochemical processes. This new method represents a major step forward in the field of limnology.
References
Verpoorter, C., T. Kutser, D. A. Seekell, and L. J. Tranvik (2014), A global inventory of lakes based on high-resolution satellite imagery, Geophys. Res. Lett., 41, doi:10.1002/2014GL060641.
Downing, J. A., et al. (2006), The global abundance and size distribution of lakes, ponds, and impoundments, Limnol. Oceanogr., 51, 2388–2397, doi:10.4319/lo.2006.51.5.2388.
