A desert is a hot area of land that gets very little rain — not more than 200mm a year. Temperatures during the daytime can get as high as 55° C. At night, deserts cool down, sometimes even below 0° C.
Deserts cover about 20% of the world's land. The biggest is the Sahara desert, which is about the same size as Europe.
Because deserts are very dry only certain kinds of plants and animals can live there.
Locations of deserts
Most deserts lie between 15° and 35° north and south of the equator. They were created by air that rises over the equator and comes down over the Tropic of Cancer and the Tropic of Capricorn. All over the world many deserts lie in these regions.
• Land over the equator becomes very hot. The hot and wet air rises and it rains a lot in these areas.
• The air cools down and moves north– and southwards. It gets drier.
• The cool air sinks to the ground. It dries out over the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
• Warm air near the surface moves back to the equator. These winds are called trade winds.
Some deserts are formed in regions that are cut off from the ocean by high mountains. Winds carry wet air from the ocean to the land. When the air climbs over high mountains it loses most of its moisture and when it falls down on the other side it becomes very warm and dry. Deserts on the western coast of North America were formed by such winds.
Many areas have become dry because they are too far away from the ocean. Air loses its moisture by the time it reaches places that are thousands of kilometres from the coast.
Deserts can also develop near the coast. Cold water moves from the Antarctic northwards along the African and South American coast. The warm air in these places cools down and mixes with the cool water. There is a lot of fog, but no rain. That's why the Atacama desert in Chile and the Namib desert in Africa are among the driest deserts in the world.
Landscapes of the desert
Only about 10% of all deserts are made up of sand. Most of them are rocky places that consist of gravel and larger stones. Desert landscapes are formed mostly by the power of the wind and water.
Strong winds form rocks in strange ways. They also build up dunes made of sand. Such dunes can be up to 200m tall and they can travel large distances every year.
After rainy times, small streams carry water. They cut their paths through the desert and carry sediments with them .These streams often end in lakes where the water evaporates and salt and minerals are left over.
Sometimes underground water comes to the surface. Such a place is called an oasis. It is the only spot where people can live, plant crops and raise animals.
Climate of deserts
In summer, temperatures may reach up to 55° C during the daytime, but at night they drop below 0° C.
Most deserts get very little rainfall— on average, not more than 20cm a year. There may be years without any rainfall at all. Sometimes a lot of rain falls during thunderstorms that last for a few hours.
When the desert dries up after heavy rainfall, salt and other minerals are left behind on the ground. Salt lakes are very common in these places. That is why some desert areas have yellow, brown and red colours.
Living in the desert
People who live in deserts must protect themselves from high temperatures during the daytime and low temperatures at night and in the winter.
Some people live in mud houses that are painted white. They keep out the heat during the daytime and protect people from cold evenings. Nomads in Africa live in tents and move around all year in search of areas with water. Many of them wear long coats that protect them from the sun and the wind.
Desert plants must change their way of life and get used to the heat and the dryness.
Some flowers only live for a few days. The seeds may be in the desert ground for years and when it rains they start to blossom.
Plants of the desert usually have small leaves that look like needles. Such plants can live with very little water, which they store in the needles or stems. Some plants have long roots that reach up to 80 metres below the surface.
Many kinds of animals live in the desert: spiders, reptiles, birds and some mammals.
Most animals stay in the shade during the daytime and look for food at night when it gets cooler. They get water from the food they eat or from the water holes in the desert. Some animals sleep during the summer.
Camels are animals that are fit to live in the desert. They can go on for days without drinking water and need only little to eat. They carry their food in their humps. They also give nomads wool and tents are made out of their skin.
The Sahara – the biggest desert in the world
The Sahara is the biggest desert in the world. The landscape is made up of mountain ranges, rocky plateaus and sandy plains called ergs. The Nile is the only river that carries water all year long. It flows through the Sahara in Sudan and Egypt.
The desert reaches from the Atlantic Ocean in the west to the Red Sea in the east – over 3,500km. The highest peaks are in the Tibesti mountains. They reach a height of about 3,500 metres.
There are about 90 bigger oases in the Sahara desert, where water comes up from underground rivers or wells. People here live in small villages and grow crops.
The Sahara also has important raw materials. Oil and gas lie under the Algerian and Libyan desert. There are also other minerals, like copper and iron ore.
About 2 million people live in the desert. Most of them are Arabs or Berbers. The Tuareg are a tribe that live in the mountainous areas of the central Sahara. Most of them are nomads who raise sheep, goats or camels and travel around all year.
In desert oases people can live the whole year. They grow dates, wheat and other crops. But, they must also fight against sand storms and wandering dunes that threaten to cover the oases with sand.
The Sahara was not always a desert. During the Ice Age, when many parts of the world were covered with snow and ice, northern Africa had a much wetter climate. The Sahara had many lakes and rivers and elephants and giraffes lived in the grasslands and forests. At about 5000 BC the climate started to become drier and the Sahara turned into a desert. Many people moved south.
Today the desert is growing because people destroy fertile land. They raise too many animals that eat all the grass or they cut down trees that still exist.