martes, 30 de julio de 2013

How much water is on Earth?


If the big bubble burst:

If you put a (big) pin to the larger bubble showing total water, the resulting flow would cover the contiguous United States (lower 48 states) to a depth of about 107 miles.

The drawings below show 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).

Sphere representing all of Earth's water

If you just want an image of all water on, in, and above the Earth, here it is.
One estimate of global water distribution
Water sourceWater volume, in cubic milesWater volume, in cubic kilometersPercent of
Percent of
total water
Oceans, Seas, & Bays321,000,0001,338,000,000--96.54
Ice caps, Glaciers, & Permanent Snow5,773,00024,060,00068.61.74
Soil Moisture3,95916,5000.050.001
Ground Ice & Permafrost71,970300,0000.860.022
Swamp Water2,75211,4700.030.0008
Biological Water2691,1200.0030.0001
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).
Note: Percentages may not sum to 100% due to rounding.

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