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Cacti dominate the Sonoran Desert
vegetation near Tucson, Arizona.
(Photograph by Peter Kresan)
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Approximately one-third of the Earth's land surface is desert, arid land with meager
rainfall that supports only sparse vegetation and a limited population of people and
animals. Deserts--stark, sometimes mysterious worlds--have been portrayed as
fascinating environments of adventure and exploration from narratives such as that of
Lawrence of Arabia to movies such as "Dune." These arid regions are called deserts
because they are dry. They may be hot, they may be cold. They may be regions of sand
or vast areas of rocks and gravel peppered with occasional plants. But deserts are
always dry.
Deserts are natural laboratories in which to study the interactions of wind and
sometimes water on the arid surfaces of planets. They contain valuable mineral
deposits that were formed in the arid environment or that were exposed by erosion.
Because deserts are dry, they are ideal places for human artifacts and fossils to be
preserved. Deserts are also fragile environments. The misuse of these lands is a
serious and growing problem in parts of our world.
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Ripples on a dune in
the Gran Desierto, Mexico.
(Photograph by Peter Kresan)
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There are almost as many definitions of deserts and classification systems as there
are deserts in the world. Most classifications rely on some combination of the number
of days of rainfall, the total amount of annual rainfall, temperature, humidity, or
other factors. In 1953, Peveril Meigs divided desert regions on Earth into three
categories according to the amount of precipitation they received. In this now widely
accepted system, extremely arid lands have at least 12 consecutive months without
rainfall, arid lands have less than 250 millimeters of annual rainfall, and semiarid
lands have a mean annual precipitation of between 250 and 500 millimeters. Arid and
extremely arid land are deserts, and semiarid grasslands generally are referred to as
steppes.
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Distribution of non-polar arid land
(Click on image to see full map)
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This page is <https://pubs.usgs.gov/gip/deserts/what/>
Maintained by Publications Service Center
Last modified 12/18/01 (krw)