what is a desert

 When we ask what is a desert ? This question leads us to the definition of the desert , So answer of the question "what is a desert " is a definitions of the desert .

Definitions of the term “desert” are neither static nor absolute. All over the world the term “desert” and its foreign-language equivalents are culturally and topographically specific. European words such as “desert,”“desert” and “Wüste” emphasize the sense of abandonment that is the standard Western response to the desert landscape—an idea that is also reflected in the etymology of the name of the Namib Desert in southern Africa— “the place where there is nothing.” Arabic has not one but several words for “desert,” including erg (applied to large areas of sand or “sand seas”) and hammada (applied to stony plains), as well as the more general sahra, from whose plural form—sahara—the world’s largest desert takes its name.


The Turkic kum means literally “sand,” reflecting the sandy wastes of Central Asia—hence the Kara-Kum, or “Black Sand,” of Turkmenistan and the Kyzyl-Kum, or “Red Sand,” of neighboring Uzbekistan and Kazakhstan—while the Persian dasht means “plain” as well as “desert,” in reference to the plateau deserts that dominate central Iran .

 Physical geographers and geologists must at least attempt to be more scientific in their definitions of what constitutes a desert, and they have debated and extended the possible meanings. Today they agree that the key determining factor is aridity, or the lack of plentiful and consistent rainfall—generally defined as less than 250 millimeters (10 in.) of annual precipitation. Such a definition extends the meaning of the desert well beyond its traditional confinement to the hot deserts that have so exercised the European imagination . low rainfall is a characteristic not only of the subtropical regions where most of the hot deserts—the Sahara, Arabian, and Australian deserts, for example—are located, but also of continental interiors, the western sides of continents, the leeward side of high mountain ranges, and parts of the Arctic and Antarctic regions.

A map showing the desert regions in the world

 Overleaf Map showing the world’s desert zones—yellow areas indicate
regions with hyperarid or arid levels of precipitation. 

Even this definition is by no means watertight; strict definitions always create seeming anomalies. The Kalahari in southern Africa is labeled a desert in every atlas, and its very name—meaning “the Great Thirst”—would appear to confirm this status. But most of the Kalahari receives roughly twice the amount of the annual maximum allowable precipitation and has a relatively rich vegetation, and therefore for some scholars this would-be desert falls outside the strict definition of the term. However, more complex definitions of aridity take into account the rate of evaporation as well as the amount of precipitation, and the Kalahari, despite its rainfall, has little standing water due to the dry heat that rapidly evaporates much of the land’s moisture. In their pursuit of exact definitions, experts have sometimes devised formulas to indicate a particular region’s “Index of Aridity.” One of the simplest, the Lang Rain Factor, for example, divides the annual precipitation (in millimeters) by the mean annual temperature (in centigrade). Other arid regions, while not generally called deserts and often receiving slightly more than the regulation 250 millimeters (10 in.) of rainfall, display some of the characteristics of the deserts. 

 Such borderline “semiarid” regions are often covered by the terms “semidesert” or “drylands.” The Sahel in sub-Saharan Africa is one important area of semidesert. In recent years this vast region has come under close scrutiny as its poor but locally crucial arable and pastoral lands have become degraded and the Sahara Desert has crept southward. 

Surprisingly perhaps, water plays a key role in shaping the desert terrain. This is because, when water does finally make its appearance in the desert, it usually does so in torrential form—powerful, destructive floods that rip through the land, sweeping away any debris or loose vegetation and over the centuries cutting channels—called “wadis” in North Africa and Arabia and “arroyos” in the Americas—deep into the landscape. Despite appearances, deserts are often mobile, changing landscapes, uniquely vulnerable to the often dramatic metamorphoses worked by weathering agents such as water, heat, and wind. Sand dunes slowly shift and grow; glistening salt pans become lakes and then dry hard again within weeks or days; and over millennia rocks are scoured and eroded into dramatic or bizarre forms, such as flat-topped mesas, mushroom-shaped zeugens, and awe-inspiring rock arches.

pictures of the desert in California
 A dry delta curls through eroded hills in California’s Death Valley, in the
rain-shadow of the Sierra Nevada, marking where a river ends in
achannel of sediment

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