Explore the fascinating characteristics of deserts including types, climate, soil, flora, fauna, and how they adapt to harsh conditions. Learn about oasis systems and human interactions with desert ecosystems.

What is a Desert?

• Defining a Desert

  • When we think of a desert, we often picture vast expanses of sand under a scorching sun. However, not all deserts fit this description. The term desert generally refers to a biome where evaporation exceeds precipitation.

  • Although a precise definition of a desert is difficult, it is commonly understood that deserts develop where the annual precipitation is less than 250 mm. Aridity, or the absence of moisture, is the common characteristic of all deserts, while temperature varies.

• Types of Deserts

  • Deserts can be classified based on temperature and precipitation patterns. They include:

    • Hot and dry deserts
    • Semi-deserts
    • Coastal deserts
    • Cold deserts

  • While sand is commonly associated with deserts, not all desert landscapes are dominated by sand. Some key types of desert landscapes are:

    • Erg: A desert covered by sand, forming dunes resembling ocean wave ridges.
    • Reg: A stony desert where wind has removed the sand, leaving angular rock fragments.
    • Hamada: A desert landscape dominated by boulders and exposed bedrock.

• Location and Formation of Deserts

  • Various factors contribute to the location of deserts. The largest hot deserts, such as the Sahara and Arabian deserts, are located in the trade wind belt near the sub-tropical high-pressure zones in both hemispheres. These regions are under the descending limb of the Hadley Cell, where air subsides, warms adiabatically, and prevents condensation and precipitation.

  • Some deserts are situated on the leeward side of mountains, where the rain shadow effect leads to desert formation. The Sonoran Desert in North America is one such example, where moisture-bearing winds are blocked by coastal mountain ranges, leaving the eastern side dry.

  • Deserts also form in the interior of continents, where the distance from the ocean prevents moisture from reaching the region. The Gobi Desert is an example of a desert formed due to both its inland location and the rain shadow effect.

  • The presence of cold ocean currents also contributes to desert formation. For example, the Kalahari Desert in Africa and the Atacama Desert in South America are influenced by the cold Benguela and Humboldt currents, which suppress rainfall.

The Biophysical Environment of Desert

• Climate

  • Desert climate is characterized by extremes. Aridity is the defining feature, with some desert areas receiving precipitation only as an exception. Deserts record the highest maximum temperatures, with the sun shining strongly during the day. However, the lack of moisture allows terrestrial radiation to escape quickly, leading to significant cooling after sunset.

  • Hot deserts are typically warm year-round, with mean annual temperatures above 20°C. Summer temperatures often exceed 40°C, and locations like Jacobabad (Pakistan), Death Valley (USA), and Azizia (Libya) have recorded temperatures exceeding 50°C. The lack of humidity and clear skies lead to high diurnal and annual temperature ranges, especially in sandy deserts.

  • Hot, dry winds such as the khamsin in Egypt and the sirocco in northern Africa contribute to harsh conditions by blowing sand across the desert.

  • Desert humidity is low, with inland areas averaging around 25%. Dry winds further reduce moisture levels. Precipitation is minimal and erratic, with some years receiving no rainfall, followed by sudden heavy showers. Rain, when it occurs, is often in the form of short, intense showers that can lead to flash floods.

  • The Atacama Desert in Chile is the driest place in the world, with some weather stations there never recording any rain. Coastal deserts, such as the Atacama and Kalahari, experience mists and fogs, which provide enough moisture to support vegetation in coastal areas.

• Soil

  • Desert soils form under arid conditions, where leaching plays a limited role. As a result, soils are rich in soluble minerals but often lack organic matter, making them pale in color (often pale grey or red). Sometimes, a layer of calcium carbonate or other soluble salts forms near the surface.

  • Despite these challenges, desert soils can be quite fertile where irrigation is available. Areas like the Nile Valley in Egypt, the Imperial Valley in the USA, and the Indus Valley in Pakistan are agriculturally productive, although careful management is needed to prevent issues like salt build-up and waterlogging.

• Flora and Fauna

  • Deserts support surprising biodiversity despite harsh conditions. Plants and animals have developed unique adaptations to cope with water scarcity and extreme temperatures. The amount and type of vegetation vary by desert; North American deserts, for instance, support more vegetation than Asian deserts.

  • The only desert areas devoid of life are the shifting sand dunes. In other parts of the desert, plants are sparse, and shrubs dominate the landscape, particularly in Asia and Africa. Plant species are usually low in height, such as the Saguaro cactus in the Sonoran Desert, which is almost tree-like.

  • Most desert plants are xerophytes, capable of surviving with minimal water and enduring long periods of drought. Some plants are halophytes (salt-tolerant), and many have deep tap roots or expansive lateral roots to access groundwater. Adaptations such as thick bark, small waxy leaves, and spines help minimize water loss and protect plants from herbivores. Some plants even resemble stones or dung to avoid being eaten.

  • Ephemeral plants can remain dormant for years and spring to life after a rainstorm, completing their life cycles rapidly.

  • Animals in the desert also exhibit remarkable adaptations. Larger animals, such as the ibex, oryx, and camels, are typically found at the desert margins. The camel, famously known as the "ship of the desert," is well-adapted to desert life. Smaller animals like rats, lizards, snakes, and scorpions are mostly nocturnal, helping them avoid the extreme daytime heat.

  • Many desert animals, such as the kangaroo rat and pocket mouse, can survive without drinking water, obtaining moisture from the food they consume. Their light-colored bodies reflect sunlight, and they have specialized adaptations, such as the absence of sweat glands and dry excrement, to reduce moisture loss.

  • Insects thrive in the brief periods when plant life is abundant, playing an important role in the desert ecosystem.

Sources of Water in a Desert

• Evapotranspiration and Water Loss

  In deserts, the loss of water from evapotranspiration exceeds the amount of water received through precipitation. As a result, there is no surplus water.

  Without a moisture surplus, the desert cannot support perennial rivers.

• Oasis and Exotic Rivers

  A permanent source of water in a desert and the vegetated area around it is known as an oasis. An exotic river has its source in a rainy area beyond the margins of the desert. The volume of water flowing in them is so large that they can carry it across the desert.

  • Examples of exotic rivers:
  • The Nile in Egypt
  • The Tigris and the Euphrates in Iraq
  • The Indus in Pakistan
  • The Colorado in the USA

  These rivers are very large, but there are also many smaller rivers that flow through deserts in other parts of the world. People living in the desert have utilized their water from ancient times. For example, the Nile supported the Egyptian civilization, while the Indus supported the Harappan civilization.

• Wadis and Natural Springs

  In deserts, there are channels that are dry except during the rainy season. These channels are called wadis in Arabic-speaking countries. Although the channel is dry on the surface, water is available below the surface. This water can be accessed with the help of wells. In some places, natural springs may also provide water. Like exotic rivers, the source of water in natural springs lies outside the desert.

• Artesian Wells

  In certain geological formations, water may be available from artesian wells. This happens when a layer of pervious rock lies between two layers of impervious rock. If the pervious layer is exposed in an area that receives enough rainfall, it may be filled with water. Natural pressure may force the water to rise up in a well bored into it at a lower level.

• Innovative Water Systems

  Communities living in deserts have devised various innovative means of obtaining a permanent supply of water. The qanat or kariz is an example of an indigenous system of transporting water common in South West Asia, especially Iran.

  • The qanat system transports water by gravity through underground tunnels from alluvial aquifers to agricultural settlements.
  • The water brought to the villages is shared through a system of community management, which ensures equitable distribution and sustainable use.

• Desalination in Desert Regions

  Today, many countries in desert regions obtain a portion of their water supply from the sea. For example, nearly all of Dubai’s water supply comes from desalination plants that remove salt from seawater and make it suitable for domestic and commercial use.

Human-Environment Relationships in the Desert

• Human Occupation in the Desert

  Deserts are sparsely populated for reasons that are not hard to understand. There are extensive stretches where there are no permanent settlements. Yet, human beings have lived in other parts of the desert for centuries. Ancient civilizations flourished in the desert, and large settlements developed around oases. Where permanent sources of water were not available, humans adopted a nomadic lifestyle. Even today, communities living in the desert show varying forms of social and economic organization and live in different stages of technological development.

• Nomadic Hunters

  The simplest forms of social and cultural organization are found among the nomadic hunters. They are the oldest inhabitants of the lands they occupy. Very few examples of these communities survive today, and those that do have been pushed to the most inhospitable parts by people belonging to more powerful groups.

  The San are an excellent example of one such group. Also known as Bushmen (a term considered derogatory today), the San are the indigenous people of southern Africa, having lived here for thousands of years. They are found in Botswana, Namibia, and South Africa, and are around 100,000 in number.

  • The San live in migratory groups, each of which has about 50 members.
  • They have an excellent understanding of the flora and fauna of their land and are skilled trackers and hunters.
  • The San use poison-tipped reed arrows and wooden clubs to hunt animals. They also dig pitfalls near waterholes to trap animals.
  • Their diet includes lizards, snakes, frogs, worms, and ant eggs. They also dig holes to find water or squeeze water from succulent roots.
  • While moving from place to place, they carry water in ostrich egg shells.
  • They live in caves, under rocky overhangs, or in crude huts made from branches and covered with animal skin and grass.
  • Domestication of animals and cultivation of plants are not practiced by the San.

  Contact with other cultural groups, both African and European, has disrupted their way of life. Their traditional weapons were ineffective against these groups, and they were soon driven away from their land. New diseases led to a decline in their population, and European hunters destroyed the herds of animals that were their food source.

  The traditional lifestyle of the San is often looked down upon, and they are encouraged to take up farming, a skill that they do not possess. Governments have relocated them under the pretext of preserving wildlife and ecosystems. However, many suspect the real reason for their relocation may be the mineral resources of the land they lived on.

• The Bindibus in the Australian Desert

  The Bindibus living in the Australian desert have a similar lifestyle. They do not cultivate land or raise animals. The only animal they have domesticated is the Dingo, a wild dog. The Bindibus are hunters and gatherers, and the Dingo assists them in tracking and running down animals like kangaroos and rabbits.

  • The Bindibus use few implements like digging sticks, grinding stones, spears, and the boomerang.
  • Their tools and weapons are made of stone and wood, as metallurgy and pottery making are unknown to them.

Nomadic Herders

• Pastoral Nomadism

  Pastoral nomadism emerged soon after humans learned to domesticate animals. This practice is common in the deserts of North Africa and West Asia, where rainfall produces wild fodder scattered in patches that can temporarily support small groups of herders. A livestock economy revolves around the care of animals and is a little more advanced than that of hunters and gatherers.

• Herding Lifestyle

  Herders move from one waterhole to the next with their flocks of sheep, goats, and herds of asses and camels. Camels largely serve as beasts of burden. They live on the margins of the desert, which are wetter, venturing into the desert only when conditions are favorable. They follow well-defined routes along which pastures and sources of water are known to be available. Regular routes also help in avoiding clashes between different nomadic groups.

  Some herders practice transhumance, migrating from lower elevations in winter to uplands in summer. The wealthier among them may own agricultural land along the route. The animals graze on the stubble in autumn, adding manure to the fields. In keeping with their nomadic lifestyles, they have few possessions, which are easily portable. Their thick, loose garments protect them from heat and cold, as well as from the strong, dust-laden winds.

• Herder Products

  Animals provide herders with milk, cheese, and meat for food. The hide and leather obtained from their skin are used to make items of clothing, tents, footwear, and water bags. The hair and wool become raw material for cloth, mats, ropes, rugs, and carpets. Surplus products are traded with merchants and cultivators to obtain food grains, dates, medicines, and manufactured products like utensils and weapons. In order to minimize risk, nomadic herders also hunt and gather, and whenever possible, grow crops and work for wages.

• Examples of Nomadic Herders

  Examples of nomadic herders include the Bedouins of Arabia, the Tuaregs of Western Sahara, the Bishari of northeast Africa, and the Kurds of Iraq, Iran, Turkey, and Syria.

  

• Challenges to Nomadism

  For thousands of years, these lands have been able to support nomadic communities as the seasonal rotation of pastures allowed them to maintain their fertility and resilience. In recent decades, however, rising human and animal populations and pressure from competing land use have led to the degradation of land and threatened the nomadic lifestyles they supported.

  Governments are encouraging the sedentarisation of nomadic groups and generally neglect pastoral communities. As a result, their traditional importance is being lost, and meat is now being imported from other countries, such as Australia. Migration along traditional routes has been disrupted by the creation of international boundaries, many of which were imposed without regard for the traditional culture of the area.

• Caravan Traders

  Caravan traders constitute another nomadic group in the desert. These merchants travel across the desert, carrying a range of goods for sale or exchange. Their business involves a huge amount of risk. Traditionally, they relied heavily on the camel, known as the "ship of the desert", as it is extremely well adapted to surviving in the desert. It can carry large loads and cover long distances, going without food and water for long stretches of time. It can also provide milk and meat, and its hair can be woven into rugs and carpets. However, the development of modern mechanized transport has reduced the role of the camel.

• Settled Cultivators

  Settled agriculture is possible only where a permanent source of water is available. Farmers have practiced agriculture along the Nile valley in Egypt for more than 5000 years. They devised a system of using floodwaters for irrigation by storing the overflow from the Nile in shallow basins that were bounded by raised banks. This water could be stored for more than a month and was lifted into narrow canals with the help of water-lifting devices, such as the shaduf and the noria, powered by animals and human beings.

  • The canals directed the water to the fields where crops such as rice, cotton, wheat, barley, beans, and other crops were grown.
  • Palm trees were also grown, with almost every part of these trees being used in one way or another.
  • Farmers kept a few domestic animals like cattle, oxen, mules, and donkeys to provide food and assist in agriculture and transportation.

  In the absence of rivers, irrigation was provided with the help of underground tunnels, or qanats, described earlier. Oases also provided water for irrigation, but the effort required to raise water was so great that their use was limited in the past. The availability of pumps in recent times has greatly facilitated its use.

• Modern Agriculture in Deserts

  The construction of dams and extensive networks of canals has changed the desert landscape in many areas. Better control over the supply of water has enabled modern farmers to cultivate two, and even three, crops every year, instead of just a single one. The Aswan dam on the Nile in Egypt has brought more than 400,000 hectares of desert land under cultivation.

  • Dams on the Indus in Pakistan, the Tigris and Euphrates in Iraq, Syria, and Turkey, and the Colorado in the USA have similarly transformed life in many parts of the desert.
  • However, the development of canal irrigation has brought along its own set of problems, such as the loss of natural fertilization provided by floodwaters and the buildup of salts in the soil.

• Mining Settlers

  Mineral wealth has attracted people to the harshest of environments, including the desert. The discovery of gold brought settlers to Karlgoorlie and Coolgardie in the late 19th century, located on the edge of the Australian desert. Similarly, diamonds, copper, silver, and uranium have drawn settlers to places like the Kalahari desert and Utah in the USA.

• Urban Dwellers

  Cities began to emerge in desert regions of Asia and Africa more than 5000 years ago. Most of them were located on the margins of deserts rather than in the center. Cities like Cairo, Damascus, and Baghdad served as centers of administration, education, religion, commerce, and transportation, and continue to do so today.

  In the past few decades, oil wealth in West Asia and North Africa has led to the founding of new cities and the transformation of older ones. Dubai is an example of a desert city known for its glitz and glamour, attracting tourists from around the world.

Environmental Problems in the Desert

• Human-Environment Relationship

  People have lived in deserts for centuries, adopting various lifestyles depending on the specific conditions of the area they inhabited. However, the human-environment relationship has not always been harmonious. There is evidence of settlements being abandoned due to the drying up of water sources. The decline of certain civilizations is attributed to reduced land productivity caused by both natural and human factors.

  Desert ecosystems are fragile, and even small disturbances can cause irreversible damage. Recovery is slow due to the extremely slow growth rate of vegetation. An increase in human and animal population, coupled with rising living standards and technological advancements, has created tremendous pressure on resources, leading to several environmental issues.

  The construction of large dams and the introduction of canal irrigation have caused problems like waterlogging and the spread of new diseases. Other serious issues, such as oil and gas production, nuclear waste dumping, and the use of deserts for nuclear testing, as well as damage to topsoil caused by heavy vehicles, are also concerning but are not discussed here.

• Desertification

  The term desertification was originally used to describe the march of the desert into neighboring areas. Today, it refers more broadly to processes leading to a decline in land productivity in arid and semi-arid regions. Human activity is the primary cause, though natural factors like climate change may also contribute.

  Desertification is categorized as:

  • Moderate (10% to 25% reduction in productivity)
  • Severe (25% to 50% reduction)
  • Very severe (more than 50% reduction)

  Gullies and sand dunes may become visible in cases of very severe desertification. It is a serious global problem affecting over a billion people, especially in cattle-rearing areas of sub-Saharan Africa, the Middle East, and West Asia.

  Desertification typically begins when natural vegetation is removed (for agriculture or fuel wood), which increases the proportion of bare ground. This results in several soil changes, such as reduced organic content, lower water retention capacity, and loss of soil structure, which decreases fertility. This, in turn, increases vulnerability to wind and water erosion. Over time, the land's character may change, altering the local climate due to changes in albedo and energy budgets.

  Human activities contributing to desertification include overgrazing, over-cultivation, deforestation, surface mining without land reclamation, faulty irrigation, and the use of heavy farm machinery.

  Efforts are underway to halt and even reverse desertification. Early monitoring, creating awareness, and educating people about sustainable resource utilization are essential steps. One such initiative is the Great Green Wall movement, which began in 2007 in the Sahel region along the southern edge of the Sahara. The movement aims to create an 8000 km line of trees to combat desertification and improve conditions in one of the poorest regions of the world.

• Salinisation

  All soils contain some salts, and the salt content of the soil is referred to as its salinity. An increase in salt concentration in the soil is called salinisation. This is a common issue in many irrigated areas, particularly where evaporation rates are high.

  Not all water applied to fields is absorbed by plants; much of it evaporates, leaving salts behind. Accumulation of soluble salts like sodium, magnesium, and calcium can adversely affect soil fertility. Salty groundwater can also contribute to the problem. If fields are flooded without proper drainage, the water table rises, bringing salty underground water to the surface. As the water evaporates, it leaves behind a salt deposit that can sometimes appear as a white crust on the soil.

  More efficient irrigation techniques can help mitigate this problem and conserve water at the same time.

• Problems Related to Climate Change

  Global climate change is expected to increase temperatures and cause irregular precipitation patterns worldwide. Higher temperatures will lead to higher rates of evapotranspiration, worsening the already dry conditions in arid regions.

  Droughts, which are common in dry land climates, are predicted to become more intense and frequent. This will significantly impact food security, ecosystems, human health, and economic growth in these regions. The sub-Saharan region, where about 23% of the population is already undernourished, is likely to be the most severely affected. The interconnection between climate change, agriculture, and poverty will worsen conditions in these vulnerable areas.