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By definition, a desert is a large and dry area that receives an extremely low amount of precipitation. In regions defined as deserts, more water is lost by evapotranspiration than falls as precipitation. In deserts, vegetation is almost nonexistent, although desert-specific animals and plants do exist that adapt to their hostile and harsh environments. Approximately 20 percent of the Earth’s land surface is covered with areas referred to as deserts.
Although the Sahara is usually considered to be the largest desert in the world, and many school books state this fact, according to the definition given above, this is not entirely true. Here we provide information that will not only help to give a correct answer, but will also help the student to better understand the meaning and importance of applying a definition. In any situation, a student must learn to understand and apply a definition in practice, instead of accepting what he is "forced" to memorize without proper understanding.
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Due to variable environments, it is impossible to give a definition of desert that would suit every case. However, the main characteristic of all deserts is the lack of moisture that is required for plant growth. This lack of moisture occurs due to a high imbalance between evapotranspiration and precipitation. The situation is worsened by several other factors, such as strong winds, high temperatures, low atmospheric humidity and rainfall timing variability.
Annual precipitation differs significantly; therefore, there are some deserts (mainly in South America) that receive almost zero inches of annual precipitation, while on the other side, some deserts, as in Madagascar, receive approximately 23 inches of annual precipitation. Despite these differences, the majority of deserts receive below 15 inches of annual precipitation. American geographer Peveril Meigs, III, classifies deserts as:
- Extremely arid lands -“true" deserts that go 12 consecutive months without precipitation
- Arid lands - less than 10 inches of annual precipitation
- Semi-deserts - between 10 and 20 inches of annual precipitation
Regions that have such minimal precipitation can hardly contribute to the production of food.
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Hot and Cold Deserts
Hot deserts are known for their extreme temperature ranges; daytime temperatures are usually extremely high (approximately 113 F, 45 C), while temperatures during the night tend to be extremely low (32 F, 0 C and below). This occurs due to water vapor, which exists in the atmosphere and eventually traps infrared radiation from both the ground and the sun. As a result, the dry desert air is not capable of trapping the heat during the night and blocking sunlight during the day. The largest hot desert in the world is the Sahara, which covers over 3,629,360 sqare miles.
Cold deserts appear in higher latitudes and, therefore, lower temperatures characterize these areas. These deserts occur for several reasons. If a certain environment is remote from the coast or if there are high mountains separating an environment from the coast, due to lack of onshore winds, a low atmospheric humidity occurs.
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The Largest Desert in the World
Determining which desert is the largest in the world depends on which definition is used. What if one uses the definition that a desert is an area that almost completely lacks plants, including areas that are too cold to support vegetation? Considering that it has a 6-inch average precipitation each year, Antarctica, which spans an area of 5,500,000 square miles, is technically the largest desert in the world.