Deserts experience some of the world's highest temperatures but perhaps more suprisingly they also undergo some of the greatest temperature contrasts to be found on the planet.

The sun beating down through clear desert skies causes the temperature in the desert to soar. But when night falls there is no cloud cover to prevent the heat radiating from the ground escaping, and no moisture in the air, which in other climates acts as an insulator. So the desert traveller may experience appalling heat during the day and a cold, even frosty night.

Deserts occur when the annual rainfall is less than about 25 centimetres (10 inches), though some deserts are colder and drier than others. The most famous desert in the world is the Sahara, covering much of North Africa, and where one of the highest ever shaded temperatures was recorded 58C (136F). But there are many other deserts too like the Simpson and Great Sandy in Australia, the Gobi in central Asia, the Kalahari in south west Africa and the Sonora desert in Mexico, to name just a few.

Deserts are not simply a result of harsh climatic conditions, though this is a certainly a large factor. The impact of man plays a part too – by removing trees and protective vegetation, and introducing livestock, which destroys much of the plant life that once existed. There is also some evidence that deserts are extending, which could have ominous effects on human populations nearby.

As in the Arctic, though for very different reasons, life is a grim struggle for desert inhabitants. Many such as the Australian Aborigines and the Tuareg of North Africa have survived as nomads, wandering after food as best they can. Occasionally oases exist such as the remarkable oasis at the Gorges du Todra in Morocco where the greenness caused by a high water table is in stark contrast to the aridity around it.

Only the hardiest of plants can survive the deserts; one of these is the cactus, now a familiar house plant in this country. It has a tough outer skin to resist the heat and is able to store large amounts of water on the rare occasions when rain falls. Other plants lie dormant as seeds for long periods, month or even years, waiting for a downpour.

When rain does eventually fall they mature and bloom very quickly and shed more seeds which in turn, will lie in wait for the next rains. This sudden flowering brings about the remarkable 'Desert Bloom' when the normally barren landscape is brightened briefly by many colourful plants. (West Australian deserts are famous for this).

Insects and snakes also cope well with these conditions. Take the sidewinder snake, for example, which has developed its distinctive sidewinding movement to ensure that not all of its body is touching the burning sand at any one time. Another hardy desert beast is the camel, which can store great amounts of water to sustain it for long periods. The camel also has the capacity to foam at the mouth when it overheats. This foam spreads over parts of the animal's body and then evaporates in the sun, so reducing its temperature.

Other features in the Climate Zones series:

- Temperate Zone
- Mediterranean Zone
- Tropical Zone
- Polar Zone
- Continental Zone
- Monsoon Zone