Desert

• Hot desert ecosystems


  • Found in North America, South and Central America, Africa, the Middle East, South Asia and Australasia
  • Around and within tropical regions, mostly around the Tropic of Cancer and Tropic of Capricorn
  • Characterised by hot seasons for most of the year, average annual rainfall below 250 millimetres, extreme daily variation in temperature from up to 50 °C during the day to below 0 °C at night, clear skies all day and night, coarse sandy soils with good drainage, little sub-surface water but low in nutrients and organic matter
• To survive in hot desert conditions requires special adaptations for plants and animals
• The hot desert ecosystem is much richer than at first sight
• Saguaro cactus


  • State flower of Arizona, USA
  • Blossoms open during desert nights and close in the day
  • Has a tall, thick stem with smooth waxy skin and 20 mm spines
  • Stem can expand to store water
• Camels


  • Called 'ships of the desert' because they can cross the desert better than any other animal
  • Have bushy eyebrows and two pairs of eyelashes to keep sand out of their eyes
  • Have thick padded feet so they can walk easily across sand
  • Only have two toes
  • Hump stores fat reserves that can be used as food as the animals travel
  • If the hump shrinks, the camel's reserves are low
• Adaptations of plants and animals to desert life


  • Low growing plants
  • Camels can store food and water for days
  • Small animals can hide in burrows or under rocks
  • Some rodents are nocturnal
  • Plants have waxy coatings to avoid water loss by strong winds
  • Plants have long roots to reach underground water supplies and to use in dry periods
  • Plants have small surface areas to prevent water loss from evapotranspiration
  • Animals can avoid intense daytime heat by being active at night
• Less rainfall and more drought will increase desertification and extend desert areas
• Increased winds will blow more sand grains onto agricultural land, reducing food supplies
• Diverting rivers for irrigation or HEP reservoirs will reduce water flow through desert areas, causing people to migrate into towns for water supplies
• Increased development of settlements and roads as countries develop their economies will change the nomadic way of life
• Hot deserts are ideal places to develop solar energy, as they receive intense sunlight and have plenty of space to build solar farms
• Tourists are looking for exciting desert activities such as camel trekking, off-road dune buggying, and star-gazing, providing income for local people
• Modern mines excavate below the water table and pump out water, making it lower, and abandoned mines leave pollutants that affect the desert ecosystem
• Nomads have moved their herds of sheep, goats and camels to find water or settle in semi-permanent oases, and camel trains have trekked across the Sahara Desert carrying goods
• Where a river is close by, some irrigation has allowed people to carry out subsistence farming and settle in villages and market towns
• Desert


  An area that receives less than 250 mm precipitation in a year
• Arid (dry) deserts


  Can be hot, like the Sahara Desert, or cold, as found in the northern tundra regions
• Hot deserts


  • Found in sub-tropical and tropical latitudes
  • Have very high daytime temperatures, often over 50°C, and low night-time temperatures, well below 0°C with clear skies and sometimes a ground frost
  • Mostly found on the western edge of continents because the prevailing winds in tropical regions are off-shore, blowing from the east across land, so they cannot pick up moisture from the sea
• Hot deserts are extreme environments which present challenges for people who live there or visit there
• Creating hot deserts


  1. Rising air at the equator cannot penetrate the tropopause, so it is diverted towards the tropics

  2. Areas of high pressure and outblowing winds, like the Sahara Desert, have descending air from the atmosphere

  3. Areas with cold ocean currents offshore, like the Namib and Atacama Deserts, have wind usually offshore but any cold moist air moving inland from the sea is warmed rapidly by the land
• The movement from rising air at the equator to descending air in the subtropics is called a Hadley cell, after George Hadley who proposed this idea in the 18th century
• Due to the heat of the sun, which is overhead at the equator, the land surfaces are warmed up and air rises, giving low pressure at the surface along the equator and thunder clouds and heavy rainfall in equatorial regions
• As the rising air at the equator moves away from the equator at high altitude, it cools, and between 20° and 35° north and south of the equator the air begins to sink or subside towards the surface, giving permanent sub-tropical high-pressure systems (anticyclones) in these areas where rainfall cannot occur, creating the hot deserts of the world