Desert is an area where annual rainfall rate is less than 254mm.
FAR FROM BEING barren wastelands, deserts are biologically rich habitats with a vast array of animals and plants that have adapted to the harsh conditions there. Some deserts are among the planet's last remaining areas of total wilderness. Yet more than one billion people, one-sixth of the Earth's population, actually live in desert regions.
What Is a Desert?
Deserts cover more than one fifth of the Earth's land, and they are found on every continent. A place that receives less than 10 inches (25 centimeters) of rain per year is considered a desert. Deserts are part of a wider classification of regions called "drylands." These areas exist under a moisture deficit, which means they can frequently lose more moisture through evaporation than they receive from annual precipitation.
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And despite the common conceptions of deserts as dry and hot, there are cold deserts as well. The largest hot desert in the world, northern Africa's Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day. But some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica. Others are mountainous.Only about 10 percent of deserts are covered by sand dunes.
The driest deserts get less than half an inch (one centimeter) of precipitation each year, and that is from condensed fog, not rain.