There are many different kinds of deserts. Those that are hot all year are called hot deserts and lie within 15 – 30 °north or south of the equator. The biggest hot desert is the Sahara in north Africa, at 5,000 km across and up to 2,250 km north to south. On average, deserts receive less than 250mm of rainfall each year.
World’s largest Hot Deserts
| Desert | Location | Size in km sq |
| Sahara | North Africa | 9 million sq km |
| Australian | Australia | 3.8 million sq km |
| Arabian | Southwest Asia | 1.3 million sq km |
| Gobi | Central Asia | 1 million sq km |
| Kalahari | Southern Asia | 520,00 sq km |
Deserts may have temperatures in excess of 40ºC during the day and yet at night, the temperature can fall to 4ºC. This is because other ecosystems are insulated by their humidity (water vapour in the air). Environments like temperate forests may have in the region of 80% humidity during the day and this water absorbs and reflects sunlight and the energy it brings. At night the water acts like a blanket, trapping heat inside the forest. Since deserts usually have only between 10 – 20% humidity to trap and have few trees or vegetation to trap heat, they cool down quickly when the sun sets and heat up quickly after the sun rises.
SoilsDesert soils are thin, not very fertile and have little organic matter. Water tends to dry off before it has the chance to sink in.
Vegetation adaptations Trees have thick bark to protect against fire.
Plant roots grow deep to soak up as much water as possible.
Desert plants such as cacti store water in stems or leaves.
Cacti have spikes to prohibit animals from eating them.
WildlifeDesert ecosystems have simple food webs, and are therefore very fragile environments. Desert animals include camels, spiders, lizards, foxes, snakes and kangaroos. Many desert animals come out in the cool of the night to find food, while some animals never drink, getting all the moisture they need from their food.
Human activityIt’s estimated that about 13% of the world’s population live in deserts and people like the Australian aborigines have lived in deserts for thousands of years, hunting and rearing animals for food and gathering plants. Their deep understanding of the desert ecosystem meant that they did not harm it.
The main conservation problem facing the world’s deserts is desertification. Desertification – expansion of the desert – is brought about by our planet’s continuously changing climate – the world is becoming warmer and drier, and this means there is less water to support plants and animals.
However, the natural rate of desertification has increased as a result of the negative effects of agriculture on the edges of desert ecosystems due to the increased pressure placed on food producers by population growth. Over-grazing by domestic animals has caused soil erosion, and the adoption of unsustainable irrigation practices for the cultivation of crops has led to the draining in a very short space of time the water sources, which may have taken thousands of years to amass. All ecosystems exist in a delicate balance, and the desert is probably the most extreme case. With all forms of life linked to one another, a change in the availability of water is potentially disastrous.