Deserts

A desert is any place that gets less than 250 millimetres of rain a year. Most people picture endless sand dunes under a blazing sun, but the world's largest desert is actually Antarctica, where the temperature can drop below -80 °C. About a third of Earth's land surface is desert.

• Definition<250 mm rainper year
• % of Earth's Landapprox. 33%covered by deserts
• Largest DesertAntarctica14 million km²
• Hottest Recorded56.7 °Cin Death Valley, USA
• Driest PlaceAtacamaparts had no rain for 400+ years
• Biggest Sand Dunes300 m+in Namib and Sahara

How big are the famous deserts?

The Sahara is huge, but Antarctica is bigger:

Area (million km²)

Antarc.14.0

Arctic13.9

Sahara9.2

Gobi1.3

Kalahari0.9

Atacama0.1

The Sahara, which looks gigantic on a map, would fit nearly seven times inside the Antarctic Desert. Both poles count as cold deserts because so little snow actually falls there.

What is a desert?

A desert is defined by how dry it is, not how hot it is. There are hot deserts (like the Sahara), cold deserts (like the Gobi in winter), and even polar deserts (Antarctica and the Arctic). The one thing every desert shares is a serious shortage of water.

How deserts form

Most deserts sit at around 30 degrees of latitude, north or south of the equator, where huge bands of dry air sink down from the upper atmosphere. Other deserts form in the shadow of mountains (the mountains catch the rain before it reaches the other side) or far inland where the sea is too distant to send moisture.

FactAntarctica is the world's largest desert. Even though it is covered in ice, almost no fresh snow falls there each year, which makes it drier than the Sahara.

Wildlife of the desert

Living without water is hard work. Camels can drink 100 litres in ten minutes and store the energy as fat in their humps. Fennec foxes have huge ears to shed heat. Cacti store water inside their stems. Reptiles like rattlesnakes and lizards stay still all day and hunt at night when the sand is cool.

People of the desert

People have lived in deserts for thousands of years. The Tuareg cross the Sahara on camels, the Bedouin live in the Arabian desert, the San bushmen know every plant in the Kalahari. Today over a billion people live in or near deserts.

Did you know?Deserts are growing. As Earth warms and humans cut down trees on the desert edge, an extra area of land roughly the size of Greece turns into desert every year. This is called desertification.

Deeper dive: the four types of desert

Geographers usually sort deserts into four families based on what causes the dryness.

• Subtropical deserts sit near the Tropics of Cancer and Capricorn. The Sahara, the Arabian, and the Australian deserts are all subtropical. Hot in summer, mild in winter.
• Coastal deserts form where cold ocean currents stop the air from holding water. The Atacama in Chile and the Namib in Africa are the classic examples.
• Rain-shadow deserts sit on the dry side of a mountain range. The Gobi in central Asia and the Great Basin in the USA are both rain-shadow deserts.
• Polar deserts are too cold for snow to fall in any quantity. Antarctica and the Canadian Arctic are the biggest examples.

Click any desert below to read its full fact file.