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Desert
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For the food course, usually served after dinner, see dessert.
Desert view in Saudi Arabia. The vast majority of the kingdom is sand desert, with distinct features and characteristics that clearly
differ between one area and another.In geography, a desert is a landscape form or region that receives little precipitation.
Generally deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 inches). The
terminology used to define deserts is complex. 'True deserts' where vegetation cover is exceedingly sparse, correspond to the
'hyperarid regions of the earth, where rainfall is exceedingly rare and infrequent. Deserts are however part of a wider classification
of regions that, on an average annual basis, have a moisture deficit (i.e they can potentially loose more than is received). These
areas are collectively called 'drylands' and extent over almost half of the earth's land surface. Because desert is a vague term, the
use of 'dryland', and its subdivisions of hyper arid, arid, semiarid and dry-subhumid, is to be preferred, and is approved by the
United Nations. Deserts have a reputation for supporting very little life, but in many deserts this is far from the truth. Deserts often
have high biodiversity, including animals that remain hidden during daylight hours to control body temperature or to limit moisture
needs. About one-fifth of Earth's land surface is desert.
Desert landscapes have certain features. Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and
stony surfaces called Reg or hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and
reflect minimal soil development and sparseness of vegetation. Bottom lands may be salt-covered flats. Eolian (wind-driven)
processes are major factors in shaping desert landscapes. Cold deserts have similar features but the main form of precipation is
snow rather than rain. The largest cold desert is Antarctica (composed of about 98 percent thick continental ice sheet and 2
percent barren rock). The largest hot desert is the Sahara.
Deserts sometimes 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 usually have an extreme temperature range. Most deserts have a low temperature at night. This is because the air is very
dry (contains little moisture) and therefore holds little heat so as soon as the sun sets, the desert cools quickly. Also, cloudless
skies increase the release of heat at night.
In the Köppen climate classification system, deserts are classed as (BW).
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