Thursday, May 31, 2012

How much water?

How much water is there on Earth?    A graphic just posted by the USGS offers a startling view.

The following is taken from the USGS website.  Read the rest of the story at

If you took all the water on earth – in oceans, ice caps, lakes, rivers, groundwater, the atmosphere, and living things – and wrapped it into a sphere, it would have a diameter of about 860 miles. That 860-mile-high sphere is represented by the largest bubble in the picture, which stretches from Salt Lake City, Utah to Topeka, Kan. It has a volume of over 332 million cubic miles. If you popped this bubble with a giant pin, the resulting flow would cover the lower 48 states to a depth of about 107 miles.

The graphic shows various blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth. These images attempt to show three dimensions, so each sphere represents "volume." Overall, it shows that in comparison to the volume of the globe the amount of water on the planet is very small - and the oceans are only a "thin film" of water on the surface.

 Spheres representing all of Earth's water, Earth's liquid fresh water, and water in lakes and rivers

The largest sphere represents all of Earth's water, and its diameter is about 860 miles (the distance from Salt Lake City, Utah, to Topeka, Kansas). It would have a volume of about 332,500,000 cubic miles (mi3) (1,386,000,000 cubic kilometers (km3)). The sphere includes all the water in the oceans, ice caps, lakes, and rivers, as well as groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant.

 Liquid fresh water

How much of the total water is fresh water, which people and many other life forms need to survive? The blue sphere over Kentucky represents the world's liquid fresh water (groundwater, lakes, swamp water, and rivers). The volume comes to about 2,551,100 mi3 (10,633,450 km3), of which 99 percent is groundwater, much of which is not accessible to humans. The diameter of this sphere is about 169.5 miles (272.8 kilometers).

Water in lakes and rivers

Do you notice that "tiny" bubble over Atlanta, Georgia? That one represents fresh water in all the lakes and rivers on the planet, and most of the water people and life of earth need every day comes from these surface-water sources. The volume of this sphere is about 22,339 mi3 (93,113 km3). The diameter of this sphere is about 34.9 miles (56.2 kilometers). Yes, Lake Michigan looks way bigger than this sphere, but you have to try to imagine a bubble almost 35 miles high—whereas the average depth of Lake Michigan is less than 300 feet (91 meters).

The data used on this page comes from Igor Shiklomanov's estimate of global water distribution, shown in a table below.

Credit: Howard Perlman, USGS; globe illustration by Jack Cook, Woods Hole Oceanographic Institution (©); Adam Nieman.

Data source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York).

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