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Desert |
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A desert is an area of land or region that gets very little precipitation
(rain, snow, hail etc.). The "technical" definition is an area that has
either less than 250 mm of precipitation per year or loses more moisture
than actually falls. Consequently vegetation cover is very sparse. Deserts
cover about one third of the earth’s surface. Because of the lack of
moisture, the dry desert air cannot block the sun’s rays during the day or
retain heat during the night. As soon as the sun sets, the desert cools
rapidly, radiating its heat into the atmosphere. This results in huge
temperature variations between day and night, ranging from 45° C during the
day in summer to freezing point at night in winter. The largest hot desert is the Sahara, where these photographs were taken. It is larger than the whole of Australia, with an area of over 9,000,000 square kilometers and covers most of North Africa. |
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