GLOWABO – Remotely Sensed Inventory of the World’s Lakes

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Up until now, there have only been estimates of how many lakes there are in the world.  Four researchers from France, Sweden, Estonia, and the United States have attempted to answer long-standing question of, “how many lakes in the world” using remote sensing techniques.

The team applied an automated algorithm called GWEM (GeoCoverTM Water bodies Extraction Method) to inventory the world’s lakes larger than 0.002 km2 in size.  The inventory collected information about lakes including abundance, size (i.e., area and perimeter), geographical distribution, elevation, and morphometric characteristics such as the shoreline development index (SDI) into a database called GLObal WAter BOdies (GLOWABO). Satellite imagery from Landsat’s GeoCover dataset was used to extract water bodies. Elevation data used in the model was from the Shuttle Radar Topography Mission digital elevation model (SRTM-DEM).

Overview of GLOWABO computations showing the data set inputs used (grey boxes), the data set outputs generated (white boxes), and the methodology used (GWEM). From Verpoorter et al, 2014.

Overview of GLOWABO computations showing the data set inputs used (grey boxes), the data set outputs generated (white boxes), and the methodology used (GWEM). From Verpoorter et al, 2014.

Before this study, there was no accurate count of how many lakes there are in the world.  A paper from 2006 estimated the number of lakes to be 304 million lakes (Downing et al, 2006).  In contrast, this study calculated 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 study excluded the world’s largest inland body of water, the Caspian Sea which has a surface area of 371,000 km2 (143,200 sq mi) as well as Antarctica and the glaciated areas of Greenland.  90 million lakes in the smallest size bin (0.002 to 0.01 km2) only collectively represent only 0.27% of the nonglaciated land surfaces.  Therefore, the researchers concluded that large and intermediate lakes dominate the total surface area of lakes.

The researchers found that lakes are not distributed equally around the world.  About 22 million water bodies larger than 0.01 km2 are located between 60°N and 56°S which is the area where elevation data is available and collectively represent 1.4% of the world’s nonglaciated surface.  A greater surface area of lakes exists north of 60°N or south of 56°S where there are about 5 million lakes.  The greatest concentration of lakes (Figures a, c, e) can be found at the boreal and arctic latitudes (45°–75°N).  Elevation also plays a role in lake size and abundance with 85% of lakes, 50% of lake area, and 50% of total lake perimeter being located at elevations lower than 500 m above sea level (Figures b, d, and f ).


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Graphs showing the geographic distribution of lakes by abundance, total area, and total area.  Source: Verpooter et al, 2014.

Graphs showing the geographic distribution of lakes by abundance, total area, and total area. Source: Verpoorter et al, 2014.

The GLOWABO dataset is a snapshot in time and is not set up to track changes in lakes.  The researchers note that: “Because of time required to compile global cloud-free imagery, regional-scale analyses are better suited to tracking changes in lake abundance.”

There are future plans, according to David A. Seekell, one of the co-authors, to make the data freely available.

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.


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