Desert

A desert is a region where precipitation is very low compared with the amount of water that could evaporate. Many deserts receive less than 250 millimetres of precipitation a year, although there is no single limit that applies to every desert. They can be hot, such as the Sahara, or cold, as in parts of Antarctica and Central Asia.

Deserts form in several settings, including subtropical belts where descending dry air limits cloud formation, regions sheltered by mountains, continental interiors far from oceans, and polar areas where very little moisture falls. Wind can move and reshape loose sediments, while occasional heavy rain may carve temporary channels and cause sudden floods.

Their landscapes vary widely: sand dunes are common in some areas, while others are dominated by gravel plains, bare rock, salt flats or dry river channels. Desert soils often contain little organic matter because vegetation is sparse. Yet deserts are not lifeless. Plants and animals have adaptations that help them cope with limited water, strong temperature changes and, in some places, intense sunlight.

Some plants store water, develop deep or widespread roots, or reduce water loss through their leaves. Many animals avoid the hottest part of the day by being active at night or at cooler times. These adaptations allow life to persist even where water is scarce and environmental conditions can change sharply.