Desert

Desert, dry region where life has extreme difficulty surviving. There are 2 types. In cold deserts, which cover about one-sixth of the earth's land area, water is unavailable during most of the year because it is trapped in the form of ice. Cold deserts include the Antarctic polar icecap and the barren wastes of Greenland. Warm deserts, which cover about one-fifth of the earth's surface, typically lie between latitudes 20° and 30° north and south, although they exist also farther from the equator in the centers of continental land-masses. They can be described as areas with annual rainfalls of 10 in (25 cm) or less. Plants may survive by being able to store water, like the cacti; by having tiny leaves to reduce evaporation loss, like the paloverde; or by having extensive root systems to capture maximum moisture, like the mesquite. Animals may be nomadic or spend the daylight hours underground. The best-known and largest warm desert is the Sahara.