LOCATION OF MAJOR DESERTS OF THE WORLD

A) AFRICA

 

B) AUSTRALIA

C) ASIA

D) NORTH AND SOUTH AMERICA

  • Deserts are formed where evaporation exceeds precipitation.
  • There are mainly two types –

Hot deserts– hot deserts of the Saharan type

Temperate desertsmid-latitude deserts like the Gobi.

 

HOT DESERT CLIMATE

A) Features

  • The aridity of the hot deserts is mainly due to the effects of off-shore Trade Winds; they are also called Trade Wind Deserts.
  • The major hot deserts of the world are located on the western coasts of continents between latitudes 25° and 35°N. and S (sub-tropical high pressure belt region- with subsiding air mass)
  • They include the biggest Sahara Desert(3.5 million square miles), Great Australian Desert, Arabian Desert, Iranian Desert, Thar Desert, Kalahari and Namib Deserts.
  • In North America, the desert extends from Mexico into U.S.A. and is called by different names at different places, e.g. the Mohave, Sonoran, Californian and Mexican Deserts.
  • In South America, the Atacama or Peruvian Desert(rain shadow effect and off-shore trade winds) is known to receive 2cm per year of precipitation

B) Temperature of Hot deserts

  • The average summer temperature is high around 30°C throughout with nearly negligible cold season intervening.
  • The highest temperature recorded is 77° C in 1922 at A1 Aziziya, Libya.
  • The reasons for the high temperatures are obvious—a clear-cloudless sky causes intense insolation to reach the ground, dry and hot subsiding air parcel and a rapid rate of evaporation.
  • Coastal deserts by virtue of their maritime influence and the cooling effect of the cold currents have much lower temperatures.
  • The desert interiors, however, experience much higher summer temperatures and the winter months are rather cold.
  • The diurnal range of temperature in the deserts are extreme and notable. Intense insolation during the day in a region of dry air and no clouds causes the temperature to rise with the sun.
  • But as soon as the sun sets, the land loses heat very quickly by radiation causing the temperature to fall quickly.
  • High diurnal temperature range is a typical feature of hot deserts. Average diurnal range varies from 14 to 25° Celsius.Frosts may occur at night during winters.

 

MID-LATITUDE/TEMPERTAE DESERT CLIMATE

  • The temperate deserts don’t receive rainfall because of continentality or rain-shadow effect or both
  • Gobi Desert is formed due to continentality and Patagonian Desert due to rain-shadow effect of the mountains.

What is Continentality?

  • It is a climatic effect that results from a continental interior being insulated from oceanic influences. Winds and air masses of moderate temperature that originate over oceans move onshore to diminish differences in winter and summer temperatures in coastal areas of continents.
  • Interiors of continents are too distant to experience the moderating effect. As a result, climates of continental interiors have great seasonal differences of temperatures and a mean annual temperature below the latitudinal average.
  • Amongst the mid-latitude deserts, many are found on plateau and are at a considerable distance from the sea. These are Ladakh, The Kyzyl Kum, Turkestan, Taklimakan and Gobi deserts of Central Asia, drier portions of the Great Basin Desert of the western United States and Patagonian Deserts of Argentina etc. (please locate these deserts on the map)
  • The Patagonian Desert is more due to its rain-shadow position on the leeward side of the lofty Andes mountain ranges than to continentality.
  • These inland basins lie hundreds of miles from the sea, and are sheltered by the high mountains all around them. As a result, they are cut off from the rain-bearing winds from the oceans.

 

 

 

 

  • Occasionally depressions may penetrate the Asiatic continental mass and bring light rainfall in winter. Due to their coldness and elevation, snow falls in winter.
  • The annual range of temperature (measuring the difference in temperature in summers and winters) is much greaterthan that of the hot deserts. Continentality leads to extremes in temperature.
  • Winters are often severe, freezing lakes and rivers, and strong cold winds blow all the time. When the ice thaws in early summer, floods occur in many places.

Rainfall (Both Hot and Cold deserts)

  • Deserts, whether hot or mid-latitude have an annual precipitation of less than 25 cm.
  • Atacama (driest place on earth) has practically no rain at all.
  • Rain normally occurs as violent thunderstorms of the convectional type.It ‘bursts’ suddenly, pours continuously for a few hours.
  • The thunderstorm is so violent, and comes so suddenly that it has disastrous consequences on desert landforms [flash floods].

 

WHY MAJOR DESERTS ARE LOCATED IN NORTHERN HEMISPHERE (between 20-30 degree north and south) AND ON WESTERN SIDE OF CONTINENT

  • The hot deserts lie along the Horse Latitudes or the Sub-Tropical High-Pressure Beltswhere the air is descending, a condition which is leastfavourable for precipitation to take place
  • The rain-bearing Trade Winds blow off-shoreand the Westerlies that are on-shore blow outside the desert limits.
  • Whatever winds reach the deserts blow from cooler to warmer regions, and their relative humidity is lowered, making condensation almost impossible.
  • There is scarcely any cloud in the continuous blue sky. The relative humidity is extremely low, decreasing from 60 per cent in coastal districts to less than 30 per cent in the desert interiors. Under such conditions, every bit of moisture is evaporated and the deserts are thus regions of permanent drought. Precipitation is both scarce and most unreliable.
  • On the western coasts, the presence of cold currents gives rise to mists and fogs by chilling the on-coming air causing it to shed whatever moisture it has as rainfall on the ocean before reaching to the continent This air is later warmed by contact with the hot land, and little rain falls. The desiccating effect of the cold Peruvian Current along the Chilean coast is extreme that the mean annual rainfall for the Atacama Desert is not more than 1.3 cm.

 

VEGETATION IN DESERTS

  • The predominant vegetation of both hot and mid-latitude deserts is xerophytic or drought-resistant.
  • This includes the cacti, thorny bushes, long-rooted wiry grasses and scattered dwarf acacias.
  • Trees here are rare except where there is abundant ground water to support clusters of date palms.
  • western coastal deserts washed by cold currents as in the Atacama Desert, support a thin cover of vegetation.
  • Intense evaporation increases the salinity of the soil so that the dissolved salts tend to accumulate on the surface forming hard pans [Bajada, Palaya].
  • Absence of moisture retards the rate of decomposition and desert soils are very deficient in humus.
  • Most desert shrubs have long roots and are well spaced out to gather moisture, and search for ground water. Plants have few or no leaves and the foliage is either waxy, leathery, hairy or needle-shaped to reduce the loss of water through transpiration.
  • The seeds of many species of grasses and herbs have thick, tough skins to protect them while they lie dormant.

 

 

 

LIFE OF PEOPLE IN DESERTS

  • Despite its inhospitable climate, the desert has always been peopled by different groups of inhabitants and tribes.

Tribe

Desert

Occupation

Bedouin Arabs Arabia nomadic herdsmen
Tuaregs Sahara nomadic herdsmen
Gobi Mongols Gobi nomadic herdsmen
Bushmen Kalahari primitive hunters and collectors.
Bindibu Australia primitive hunters and collectors.

A) The settled cultivators

  • The Egyptians has been able to raise many crops as early as 5,000 years ago because of the NILE river
  • Modem concrete dams constructed across the Nile e.g. Aswan and Sennar Dams improved agriculture.
  • In the same way, desert cultivators rely on the Indus in Pakistan, the Tigris-Euphrates in Iraq, and the Colorado in the Imperial Valley of California.
  • In the deserts, wherever there are oasis, some form of settled life is bound to follow. These are depressions of varying sizes, where underground, water reaches the surface.
  • Some of them are abnormally large like the Tafilalet Oasis in Morocco which measures 5,000 square miles.
  • A wall is usually constructed around the oasis to keep out the violent dust storms called
  • The most important tree in the oasis is the date palm. Date fruit is consumed locally and also exported.
  • Other crops cultivated include maize, barley, wheat, cotton, cane sugar, fruits and vegetables.

B) The Mining settlers

  • It was gold that brought immigrants scrambling into the Great Australian Desert.
  • Some of these regions like Kalgoorlie and Coolgardie have become towns of considerable size.
  • In the Kalahari Desert, the discovery of diamonds and copper has brought many white men to the ‘thirst land’.
  • Even in the most arid Atacama, in northern Chile, large mining camps have been established for the mining of caliche (cemented gravels)from which sodium nitrate, a valuable fertilizer, is extracted and exported to all parts of the world.
  • Besides nitrates, copper is also mined. Chuquicamata is the world’s largest copper town.
  • In the North American deserts, silver is mined in Mexico, uranium in Utah and copper in Nevada.
  • In recent years, the discovery of oil, in many parts of the Saharan and Arabian Deserts has transformed these regions with Saudi Arabia, Iran, Iraq, Kuwait, Algeria, Libya, Lebanon, Nigeria becoming important oil producing desert countries of the world.

 

DESERTIFICATION

Desertification is defined as a process of land degradation in arid, semi-arid and sub-humid areas due to various factors including climatic variations and human activities.

A) Causes of Desertification

  • Overgrazing: Animal grazing is a huge problem for many areas that are starting to become desert biomes. If there are too many animals that are overgrazing in certain spots, it makes it difficult for the plants to grow back, which hurts the biome and makes it lose its former green glory.
  • Deforestation: When people are looking to move into an area, or they need trees in order to make houses and do other tasks, then they are contributing to the problems related to desertification. Without the plants (especially the trees) around, the rest of the biome cannot thrive.
  • Farming Practices: Some farmers do not know how to use the land effectively. They may essentially strip the land of everything that it has before moving on to another plot of land. By stripping the soil of its nutrients, desertification becomes more and more of a reality for the area that is being used for farming.
  • Urbanization and other types of land development. As mentioned above, development can cause people to go through and kill the plant life. It can also cause issues with the soil due to chemicals and other things that may harm the ground. As areas become more urbanized, there are less places for plants to grow, thus causing desertification.
  • Climate Change: Climate change plays a huge role in desertification. As the days get warmer and periods of drought become more frequent, desertification becomes more and more eminent. Unless climate change is slowed down, huge areas of land will become desert; some of those areas may even become uninhabitable as time goes on.
  • Stripping the land of resources. If an area of land has natural resources like natural gas, oil, or minerals, people will come in and mine it or take it out. This usually strips the soil of nutrients, which in turn kills the plant life, which in turn starts the process toward becoming a desert biome as time goes on.
  • Natural Disasters:There are some cases where the land gets damaged because of natural disasters, including drought. In those cases, there isn’t a lot that people can do except work to try and help rehabilitate the land after it has already been damaged by nature.

B) Effects of Desertification

  • Farming becomes next to impossible. If an area becomes a desert, then it’s almost impossible to grow substantial crops there without special technologies. This can cost a lot of money to try and do, so many farmers will have to sell their land and leave the desert areas.
  • Hunger:Without farms in these areas, the food that those farms produce will become much scarcer, and the people who live in those local areas will be a lot more likely to try and deal with hunger problems. Animals will also go hungry, which will cause even more of a food shortage.
  • Flooding:Without the plant life in an area, flooding is a lot more eminent. Not all deserts are dry; those that are wet could experience a lot of flooding because there is nothing to stop the water from gathering and going all over the place. Flooding can also negatively affect the water supply, which we will discuss next.
  • Poor Water Quality: If an area becomes a desert, the water quality is going to become a lot worse than it would have been otherwise. This is because the plant life plays a significant role in keeping the water clean and clear; without its presence, it becomes a lot more difficult for you to be able to do that.
  • Overpopulation:When areas start to become desert, animals and people will go to other areas where they can actually thrive. This causes crowding and overpopulation, which will, in the long run, end up continuing the cycle of desertification that started this whole thing anyway.
  • Poverty:All of the issues that we’ve talked about above (related to the problem of desertification) can lead to poverty if it is not kept in check. Without food and water, it becomes harder for people to thrive, and they take a lot of time to try and get the things that they need.

C) Solutions for Desertification

In 1994, the United Nations established the Convention to Combat Desertification (UNCCD), through which 122 countries have committed to Land Degradation Neutrality targets, similar to the way countries in the climate Paris Agreement have agreed to targets for reducing carbon pollution. These efforts involve working with farmers to safeguard arable land, repairing degraded land, and managing water supplies more effectively.
  • Policy Changes Related to How People can Farm. In countries where policy change will actually be enforced on those in the country, policy change related to how often people can farm and how much they can farm on certain areas could be put into place to help reduce the problems that are often associated with farming and desertification.
  • Policy Changes to Other Types of Land Use. If people are using land to get natural resources or they are developing it for people to live on, then the policies that govern them should be ones that will help the land to thrive instead of allowing them to harm the land further. The policy changes could be sweeping or they could be depending on the type of land use at hand.
  • Education:In developing countries, education is an incredibly important tool that needs to be utilized in order to help people to understand the best way to use the land that they are farming on. By educating them on sustainable practices, more land will be saved from becoming desert.
  • Technology Advances.In some cases, it’s difficult to try and prevent desertification from happening. In those cases, there needs to be research and advancements in technology that push the limits of what we currently know. Advancements could help us find more ways to prevent the issue from becoming epidemic.
  • Putting Together Rehabilitation Efforts. There are some ways that we can go back and rehabilitate the land that we’ve already pushed into desertification; it just takes some investment of time and money. By putting these together, we can prevent the issue from becoming even more widespread in the areas that have already been affected.
  • Sustainable practices to prevent desertification from happening. There are plenty of sustainable practices that can be applied to those acts that may be causing desertification. By adding these to what we should be doing with land, we can ensure that we don’t turn the entire world into a desert.

 

VIDEOS/DEBATES TO WATCH FOR

Fight against Desertification:

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