Facts about Deserts
Deserts cover one-fifth of the Earth’s surface and are fascinating places. Take the Namib in southern Africa. Considered the world’s oldest desert, it may have been dry for 1 million years. The Namib reaches the sea along the barren Skeleton Coast, which is named after the shipwrecks that litter the dunes. South of the Skeleton Coast is the Sperrgebiet (which translates as ‘prohibited area’), where public access is restricted to prevent diamond hunters combing the coastal dunes for gems.
The Namib is a hot desert with summer temperatures reaching 30-40 degrees Celsius (86-104 degrees Fahrenheit), but deserts can be cold too; for instance, the ice-covered continent of Antarctica is Earth’s largest desert. A desert is simply a place where average rainfall is less than 0.5 metres (1.6 feet) per year. Indeed, some deserts remain rainless for months or even years.
Most of Earth’s hot deserts lie within 30 degrees latitude of the equator. Examples include Africa’s vast Sahara Desert. Gigantic atmospheric currents force air to sink and warm at these latitudes, which in turn suppresses rainfall.
The Namib and Atacama are coastal deserts lying beside cold ocean currents – the Benguela and Peru Currents, respectively – that cause air above them to cool. Cold air can hold less water, reducing the rain falling on nearby warm land. These deserts are among Earth’s driest. Most moisture here comes from desert fogs, which form when warm air condenses over the cold ocean.
Some deserts in central Asia and Australia lie in continental interiors, so damp ocean air loses most of its moisture before it can reach them.
Desert climates and wildlife vary drastically. Hot deserts like the Sahara are warm year-round and rain is scarce.
Temperatures can reach 49 degrees Celsius (120 degrees Fahrenheit) during the day, but at night can plunge to -18 degrees Celsius (-0.4 degrees Fahrenheit). Clear skies allow heat to escape after sunset and small mammals forage at dusk. Plants include ground-hugging shrubs with leathery leaves.
In semi-arid deserts, like the US Great Basin’s sagebrush, temperatures rarely fall below ten degrees Celsius (50 degrees Fahrenheit) or rise above 38 degrees Celsius (100 degrees Fahrenheit). Spiny plants like the creosote bush thrive here.
Close to cold ocean coasts, desert summer temperatures rarely rise above 24 degrees Celsius (72 degrees Fahrenheit) and yearly rainfall can be 13 centimeters {five inches). Plants have roots close to the surface to collect rain and fleshy, water-storing stems. Some toads remain dormant in burrows for months between rainstorms.
Desert ecosystems are damaged by things like off-road vehicles, drilling and mining. Higher temperatures due to climate change could threaten drought-adapted wildlife by increasing fires as well as drying out waterholes.
Explore desert landscapes
Dunes aren’t the only desert terrain. Learn about salt pans, oases, wadis and more:
Mesas and buttes – Flash floods wear away the bare sides of plateaux where soft sedimentary rocks lie beneath hard lava. Isolated flat-topped hills called mesas and buttes are left behind.
Canyon – Desert canyons form over millions of years. Rock, sand and water carried down wadis by flash floods cut deep channels into a plateau.
Plateau – Plateaus are large flat highlands that rise more than457m (1,500ft) above their surroundings and have at least one steep side.
Alluvial fan – Flash floods lose energy at the mouth of a wadi as the water fans out. The flood drops its load of sand and rocks to form a cone of debris.
Dune field – Dunes cover about 25 per cent of Earth’s deserts. The diagram shows barchan dunes towards the edge of the dune field. Barchans form when sand is scarce – less than 10m (33ft) deep.
Pediment – Pediments are gentle slopes at the base of desert cliffs. No one is certain how they form. One theory is they’re carved by sheets of debris-laden floodwater.
Rocky desert – Nearly 75 per cent of deserts are stone-covered or bare rock plains. Rainfall, wind, temperature and rock type affect how the desert looks.
Oasis – Oases have lush vegetation and often surround a spring. They are fed by underground rivers or water-filled rocks that sit close to the surface.
Salt pan – Salt pans, or playas, are flat areas covered with salt and dried-out lake beds. Water evaporates faster than the lake refills by rainfall leaving salt and minerals behind.
Wadi – Wadis can be deadly. These riverbeds are usually dry, but can flash flood in minutes after heavy rain. The flood possesses enough power to carry large boulders and sweep people away.
Read also about Deserts and The Desert Biome(s)
Life at the deserts
Camel – Camels can drink an incredible one-third of their body weight in ten minutes, and store water by diluting their blood. They chew thorny plants with their thick lips. Their fat-filled humps both insulate them against the beating Sun and serve as a source of energy during food shortages.
Addax – Addaxes are Earth’s most desert-adapted antelopes. Broad, flat-soled hooves stop them sinking into sand, while their brown coats turn white in summer to reflect sunlight and keep them cool. Addaxes search the Sahara for grasses and shrubs to eat, which provide all the water they need.
Spotted hyena – Spotted hyenas are Africa’s commonest large carnivore and live in semi-desert. They thrive by scavenging almost anything, including putrid meat, cooked porridge, animal droppings, bones and vegetables. Powerful jaws and stomach acid allow them to digest all parts of an animal except the hair and hooves.
Welwitschia plant – Welwitschia are leathery succulent plants that rely on desert fog and dew for water. Found along the Namib Desert coast where no rain falls some years, they collect fog through numerous tiny pores on their leaves. Their long taproot can reach underground water too.
Kangaroo rat – Kangaroo rats never need to drink. Their kidneys extract water from their food, which includes insects, grass, leaves and seeds from creosote bushes. To make dry seeds succulent, they store them in humid burrows to absorb water.
Black-tailed jackrabbit – Black-tailed jackrabbits are hares, not rabbits. They have black-tipped ears, which are a huge 12.5cm (5m) long; these lose heat to keep the animal cool. Jackrabbits shelter from the Sun in hollows beneath shrubs or grass and forage in the cool of evening.
Saguaro cactus – The saguaro is North America’s largest cactus and can reach 15m (50ft) tall and weigh six tons. Cacti are botanical water balloons. Expandable wooden ribs support each plant’s pulpy body allowing it to inflate to store rain. To reduce water loss, they have no leaves and spines protect them from predators.
Creosote bush – Creosote bushes in the Mojave Desert could be Earth’s oldest living plants – perhaps 11,700 years old. Creosote grows in US deserts and can survive two years without rain. Small, waxy leaves reduce moisture loss and drop off during dry periods. These shrubs only flower after rain.
Thorny devil – Thorny devils catch morning dew and rainwater in tiny grooves between the scales on their belly and legs. They can gather as much as 1g (0.04oz) during a rainstorm. The lizard gulps to move water from the channels up into its mouth.
Sahara Desert ant – One of Earth’s most heat-tolerant insects, these ants withstand surface temperatures of 60”C. Long legs raise their bodies above hot ground and they sprint to minimize sunlight exposure. Desert ants count their footsteps to avoid getting lost instead of leaving a chemical trail, which would evaporate.
Roadrunner – Roadrunners aren’t ditzy or blue, but are well-named as they sprint from danger at 32km/h (20mph). To save energy, they cool down at night and they warm up by turning their backs to bathe in morning sunlight.
Meerkat – Meerkats absorb heat on cold mornings by exposing their dark bellies, which have little hair. Like many desert animals, they get all their water from food. Dark circles around their eyes reduce glare from the Sun, while a special membrane across their eyes keeps out any sand in the air.