Deserts of the World

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Earth from Apollo 8

This photograph shows the continent of Africa and the Arabian Peninsula. The Sahara, Kalahari, and Arabian deserts (as well as southwestern Madagascar) are clearly visible as brown-colored areas. Clouds cover much of central Africa. The dark band immediately to the south of the Sahara is known as the Sahel, the Arabic word for "shore." When Arab merchants and soldiers arrived in North Africa around 650 a.d., shortly after the Islamicization of Arabia, they became aware that the Sahara's southern boundary advanced and receded like oceanic tides.

Deserts are Dry

In what way are Antarctica and the Sahara similar? Both can be called "deserts." Desert climates are dry, but a lack of precipitation is not the end of the story. For a region to be a desert, the annual potential evaporation must be greater than the annual precipitation. In fact, it is better to refer to deserts as drylands. The drylands of the world can be classified along a continuum ranging from subhumid to hyperarid, as the figure below shows.

Half the countries on earth lie partly or entirely in the arid and semiarid zones, which cover one-third of the planet's land surface, 44 percent when the subhumid zone is included. In 1950, the population of these countries was 76 million; in 1985, population reached 205 million. The forecast for 2000 is for 300 million people to be living on the Earth's drylands.

The correct citation for this chart is:
Milich, L., 1997. Deserts of the world. http://ag.arizona.edu/~lmilich/desert1.html.

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Desert Locator Maps with Climate Classifications

Desert geomorphology

Cryptic Life
This site last updated October 30, 1998.