Desert

What you’ll learn on this page

  • What defines a desert
  • How rain and temperature affect deserts
  • The role of rocks, sand and dust in deserts
  • The characteristics of animals and plants found in deserts
  • Different types of deserts
  • Information on the Saharan and Antarctic deserts

Deserts are the Earth’s driest environments. They cover approximately one-third of the Earth’s land and are found in all seven continents. A desert is an extreme environment and is particularly tough to live in. Regardless, many plants, animals and microscopic organisms have evolved to survive even in the harshest of the world’s deserts.

Desert ecosystems are especially common in Australia, Africa, the Middle East and Antarctica. By definition, a desert is any area of land that receives less rain than it is loses through evaporation and transpiration. Because more sun leads to more evaporation and transpiration, deserts are mostly found in hot, tropical areas but they also in colder regions from sub-tropical ll the way to the polar regions of Antarctica and the Arctic.

As deserts determined by the amount of rain an area receives, a desert does not necessarily have to be a hot place. In fact, the polar regions of Antarctica and the Arctic are both deserts because they only receive tiny amounts of rain each year.

Regardless of the average temperature, desert environments receive an average of less than 250 mm (10 in) of rain per year and many deserts receive far less than that. As ecosystems, they are characterized by hardy plants and animals that can tolerate harsh temperatures and low water availability.

Rain

Precipitation, or lack of, is the driving abiotic factor in desert environments. As deserts receive very little rain they are dry, dusty environments and are only inhabited by tough, drought tolerant organisms.

A desert averages less than 250 mm of rain per year and the lack of rain drives the formation of desert ecosystems. Semi-deserts receive between 250-500 mm of rain a year and hyper-arid deserts must deal with an average rainfall of less than 50 mm per year. Many hyper-arid deserts go multiple years without seeing any rain. To put this into perspective, a torrential down pour can drop more than 25 mm of rain in less than 2 hours.

It is common in many deserts that when rain does arrive it falls in heavy belts. Because the ground is so dry and hard, only a small amount of water actually penetrates the ground’s surface and most of the rain stays above-ground. This often leads to flash floods and commonly the flooding occurs down land from where the rain fell.

Desert mountainsTemperature

Although deserts are almost always portrayed as extremely hot places, they can actually be any temperature. Deserts in tropical areas are typically extremely hot environments and often hit temperatures of over 45˚C (115˚F) during the day. With almost zero cloud cover, the daytime heat is quickly lost after the sun has set and night-time temperatures can drop below 0˚C.

Cold deserts or temperate deserts are found in colder latitudes. In cold deserts the air contains very little moisture often because it has already fallen as rain or the air is too cold for moisture to exist. Cold deserts can sometimes be found in alpine zones, in the center of continents and in the polar regions of Antarctica and the Arctic. In the poles, the very little precipitation that does occur falls as snow.

Desert rock and sand

Deserts often consist of a rocky terrain littered with scarce vegetation. Around 20% of the most extreme hot deserts are completely covered in sand and support no vegetation at all.

Ras-al-khaimah desertThe drastic shift between hot days and cold nights is harsh on rocks and the terrain is gradually split into pieces. When rain does arrive, water seeps through the sun scorched rock and can cause rocks to shatter. In deserts, rocks are often quickly weathered down to sand and dust.

Winds pick up the dust and sand and in certain areas sand can accumulate to form great sand dunes. Other areas are swept clean by the wind leaving behind smooth, rocky surfaces.

Sand and dust storms

Sand and dust storms are natural phenomena experienced in many deserts around the world. Large amounts of dust and sand, coupled with a lack of protection and buffering from plants, commonly exposes deserts to the threat of sand and dust storms.

Dust and sand storms usually begin at the edge of deserts where the particles are the smallest and easiest to be lifted by wind. Dust storms are far more frequent because dust particles are far smaller than sand. A single dust storm can rise 6 km into the sky and travel over 6000 km of land.

Sand storms are much smaller and often follow a dust storm. Because sand is larger and heavier, sand storms don’t grow anywhere near as high as dust storms. Typically, sand storms grow less than 1 m high and each sand particle is only carried a few yards at a time. It isn’t uncommon for sand storms to interfere with electrical equipment due to electrical charges produced between sand particles within the storm.

ScorpionLiving in deserts

Deserts are extreme environments to live in. The plants, animals and microbes that inhabit the Earth’s deserts must be well adapted to tolerate their harsh living conditions. As such the organisms that are found in deserts have evolved some serious adaptations to survive there. Factors such as the lack of water, extreme temperatures, evaporation rate and ground water supply have each played a role in the evolution of specialist desert species.

Animals that live in deserts

The main problems that desert-dwelling animals encounter in their struggle for survival is access to drinking water and extreme temperatures – both hot and cold. To combat these environmental adversities the animals of deserts have evolved morphological, physiological and behavioral adaptations to help them survive.

Many animals that live in deserts are nocturnal, spending their days sheltered from the sun and their nights foraging. Smaller animals will often burrow underground during the day to avoid the sun. Other animals, such as kangaroos in Australia, spend the majority of their days under the shade of a tree.

Birds are arguably the most successful inhabitants of deserts because they are able to escape the daytime heat of the desert floor by flying up into cooler air at higher altitudes. They also have the advantage of being far more effective at finding and travelling between water sources than non-flying animals.

Access to water is a recurring issue for any animal living in a desert. Most animals are highly efficient with their water use and obtain most of their water from their food. Many species have concentrated urine to reduce water loss. Camels are the iconic mammals of hot deserts and are brilliantly adapted to living there. Their urine is super concentrated, their feces is dry and they can amazingly withstand losing up to 40% of the body weight from water loss without dying of dehydration.

Many unique reptiles and invertebrates also make deserts their home. Snakes and lizards are particularly common in hot deserts but are not found in cold deserts. Scorpions are one group of invertebrates that are found exclusively in desert environments.

Plants that live in deserts

Plants must deal with the same problems animals face, except they don’t have the luxury of escaping the harsh conditions by finding shade or travelling to the nearest water source. To deal with the water deprivation that comes with living in deserts plants can utilise one of two strategies. They can either tolerate the severe droughts that occupy deserts for most of the year or they can avoid them.

Drought tolerant plants are extremely efficient with their water use and are able to survive extensive periods without access to water. Some plants have the ability to lose 70% of the weight in water loss and still survive. Other species of plants, such as cacti, make efficient use of the irregular rain events and store excessive amounts of water in their succulent tissue to see them through to the next down pour. Desert plants that have evolved to tolerate severe droughts are often either succulent with small/no leaves but spikes to prevent being eaten or tough and wiry in appearance.

Desert shrubPlants that have opted for the strategy to avoid the severe droughts of the desert have a short window of opportunity to grow. There are a number of short-lived plant species in deserts that have evolved to grow quickly after rain, rapidly produce flowers and seeds, and then die back only after a period of a couple of weeks. These plants never have to deal with the issue of an insufficient availability of water that the remaining plants (and animals) have to deal with.

A group of specialist desert plants have evolved a unique method of photosynthesis. The CAM photosynthesis pathway increases the efficiency of water use for plants by reducing the amount of water lost during photosynthesis.

In order for plants to collect carbon dioxide (CO2) from the atmosphere for photosynthesis they must open pores in their tissue to allow CO2 to enter. While the pores are open, water is free to escape from the plant’s tissue out to the atmosphere. In most environments this isn’t an issue because water is readily available and plants can easily replenish any water that is lost.

In deserts where water isn’t readily available, plants use the CAM photosynthesis method to reduce their water loss by only opening their pores during the night. They store the CO2 they have collected until the next day and then use the sun’s energy to complete the remaining steps of photosynthesis.

Types of deserts

Deserts can be categorized by a number of factors such as yearly rainfall, temperature and location. As such there is a huge range of different types of deserts.

Differences in the amount of annual rainfall between deserts separates deserts into semi-deserts, arid deserts and hyper-arid deserts. Semi-deserts receive between 250-500 mm of rain a year. An arid desert has an average annual rainfall between 50-250 mm and a hyper-arid desert receives less than 50 mm of rain per year. To put that into perspective, a torrential down pour can drop over 25 mm of rain in less than 2 hours and many places receive more rain in one day than deserts do in an entire year.

Deserts defined by temperatures are generally split simply into hot and cold deserts. Hot deserts are hottest during the summer and typically have low cloud cover and low humidity. Rainfall is usually very variable both in the frequency and intensity of rain events. Hot deserts are most common in tropical and sub-tropical regions. Cold deserts are found further from the equator and are created due to very low levels of moisture in the air.

Some common types of deserts based on location include polar deserts, coastal deserts and montane deserts. Polar deserts are a type of cold desert and include the vast majority of Antarctica and parts of the Arctic. The air is extremely cold at the poles and any precipitation that does fall does so as snow. The central areas of the Antarctic continent are almost hyper-arid deserts and receive around 50 mm of precipitation per year.

Coastal deserts are most commonly found on the west coasts of continents and occur in coastal areas where cold water currents run along the coast. The cold water produces very little amounts of evaporation and onshore winds only pick up small amounts of moisture before they blow over land. A lack of moisture in the air leads to small amounts of rain.

Coastal deserts are often narrow and sandwiched between the coast and a mountain range. The Atacama Desert in Chile is one of the world’s driest locations and is nestled between the Chilean coast and the mountains of Patagonia. Some areas of the Atacama Desert receive an average of less than 1 mm of rain per year.

Montane deserts are arid places at high altitude. They are usually found far from the coast or any large body of water. Montane deserts receive very little amounts of rain because any moisture in the air is likely to fall well before the air reaches them.

Saharan desert

The Saharan desert is the world’s largest hot desert. It stretches approximately 5000 km (3000 miles) across the top of the continent of Africa and 2000 km (1200 miles) north to south down to central Africa. It covers a total of around ~9.1 million km² or 3.5 million square miles, a similar size area to the USA or China.

The Saharan desert is one of the hottest and driest places on Earth. A number of regions go without any rain for multiple decades and the central regions are hyper-arid deserts with next to no vegetation. Even though much of the desert has very little vegetation, around 2,800 species of plants live in the Saharan desert. The plants are accompanied by a number of tough mammals, birds, reptiles and invertebrates that can amazingly survive in one of Earth’s harshest environments.

Antarctic desert

Antarctica is the world’s largest desert and covers more than 14 million km² or 5.5 million square miles, more than 1.5 times the size of the Saharan Desert. It is obviously a cold desert and temperatures have been recorded below an insanely cold -90˚C (-130˚F).

It does not rain in Antarctica and very rarely snows. When it does snow, strong winds often quickly create a blizzard. Very few plants are able to survive there and of those that can most are non-vascular plants such as mosses. Lichens are far more common than plants.

Animal populations are supported by marine productivity and other than invertebrates only seals and birds are found on the continent. The only vertebrate animal to overwinter on the Antarctic continent is the Emperor penguin.


Summary

  • Deserts are dry areas of land that receive an average of less than 250 mm of rain each year and lose more water through evaporation and transpiration than they receive from rain.
  • Both the hottest and the coldest places on Earth are deserts.
  • Hot deserts are often exposed to dust and sand storms. Dust storms are much larger and are far more common.
  • The organisms that live in deserts have to find ways to overcome the lack of water.
  • Many animals in hot deserts are nocturnal and burrow underground during daytime to avoid the heat.
  • Plants can either tolerate life with limited water supply or avoid the lack of water by only growing for short periods following a rain event.
  • Different types of deserts can be classified by their annual rainfall, temperature and location.
  • Antarctica is the world’s largest desert and the Saharan desert is the world’s largest hot desert.

Last edited: 16 January 2016

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