A desert is a place that gets just a bit of rain every year.
Some deserts get almost no rain at all.
A desert can be very hot in daytime and cold at night.
Some deserts are cold all the time.
To live in a desert, plants and animals need special habits.
The term biome means the main groups of plants and animals living in areas of particular climate patterns, and includes the way in which animals, plants and soil interact together.
What plants can grow in an area is determined by the typical weather and seasons, and this in turn determines what kind of animals can survive there.
A desert is a dry area where less than 50 cm of rain falls each year. About one fifth of the Earth's surface is desert. Deserts can be hot or cold places.
The Australian desert is one example of a hot desert, and the Gobi desert in Mongolia is an example of a cold desert.
Antarctica is the world's largest desert, and the Sahara Desert is the largest hot desert.
The Atacama desert of Chile and the Sahara desert in Africa receive less than 1.5 cm a year, if at all.
Although rain doesn't fall very often in deserts, sometimes not for years, there can be sudden, heavy rains that cause flooding.
Deserts can be found along coastlines, such as the Atacama desert, or in the interior of continents, such as the Great Basin desert of North America.
The location of the desert and of mountain ranges help determine what type of desert it is. Coastal deserts are located on west coasts of continents. The winds blow in an easterly direction and prevent the moisture from moving onto the land.
Some deserts, like the Gobi desert, are affected by high mountain ranges that produce a rainshadow effect, which means the mountains prevent moisture from reaching an area.
The Himalaya Mountains prevent rainfall from reaching the Gobi desert .
Because they are dry, hot deserts have wide variations in temperature each day. In the daytime when there is little moisture in the air to block the sun's rays, it becomes very hot. When the sun goes down, the heat absorbed by the ground during the day quickly evaporates into the air and the temperature becomes very cold. This variation of temperatures is one of the things that makes survival in the desert very difficult.
The amount and kinds of plants vary according to where the desert is located. Short grasses can be found in nearly all deserts.
Desert plants include sagebrush, creosote bushes and cacti. The saguaro (say suh where-oh) cactus is found only in the Sonoran type desert of North America and spinifex is found in the Australian desert.
Plants have had to develop different ways of capturing water in order to survive in the dry climate. This is called adaptation.
A common adaptation is to store water in the roots, stems, leaves or fruit. Plants that store water in this way are called succulents, one of which is the cactus.
Some plants have developed very long roots that go deep into the ground to reach underground water. Huge baobab trees in Africa and Australia store water in their trunks. Others have developed spreading root systems lying just below the surface and stretching widely. This gives the plant many tiny roots that capture water when it rains.
The Australian mulga tree has a unique way of collecting water. Its tiny leaves grow upward, forming a series of funnels that send rain water along the branches and down the trunk to the ground, where the roots are concentrated close to the base of the tree.
There are desert plants that are activated when rain does come, grow, flower and seed within just a day or so when there is moisture. Then they are dormant (like being asleep) until the next rain comes, however many years that may be.
Desert plants limit water loss through their leaf surface by adapting the size, sheen, or texture of their leaves. Small or spiny leaves limit the surface area exposed to the drying heat. Glossy leaves reflect the sun's rays, reducing leaf temperatures and evaporation rates. Waxy leaves prevent moisture from escaping. Some plants only open their leaf pores at night when it is cool and water loss from leaves is low.
Deserts are home to many reptiles, insects, birds, and small mammals. Few large animals have adapted to desert life because their size makes it difficult to find shelter from the heat and they are not able to store water.
Australia's bilby and the kangaroo mice of North America are just a few examples of small mammals that live in the desert. Many reptiles live in deserts. They are small and find shelter more easily than larger animals, and they eat less.
In order to survive, desert animals have developed a number of ways of adapting to the desert. The most common adaptation in behaviour is staying in shade of plants or rocks or by burrowing underground in the heat of the day. Many are nocturnal: they stay inactive during the day and hunt at night when it is cold. Some animals get all of the moisture they need from the insects, plants and seeds they eat, and do not need to drink water. Most pass little moisture out of their bodies. They do not have sweat glands and pass only small amounts of concentrated urine.
Fat increases body heat, so some desert animals have concentrated the body's fat in one place, such as a hump (like a camel) or tail, rather than having it all through the body.
There are a surprising number of frogs in the Australian desert. Their adaptation is to burrow deep into the ground where they hibernate until heavy rain wakes them up. They have a short time in which to breed, and their tadpoles grow quickly in small puddles and become adults that then burrow and wait for the next rain.