Hot Deserts

• Why deserts are NOT located at the equator

  1. The sun's rays are more concentrated at the equator, so it is the hottest part of the earth

  2. This intense heat warms the land, the air and the sea and causes water to evaporate into the air

  3. This very warm, moist air then rises

  4. Once the warm air rises it cools and the water turns back into rain, creating clouds

  5. This means that although it is hot, there is lots of rain at the equator (hence rainforests are located here, NOT DESERTS!)
• Where deserts are located

  1. Equator is VERY hot

  2. Warm air rises

  3. By the time it reaches 30N or South the air has lost any moisture

  4. It starts to cool down as it gets further away from the equator and the cool, dry air sinks back down

  5. As it gets closer to the EQUATOR again it heats back up and the process repeats
• Soil in a desert

  It is usually shallow with a coarse, gravelly texture. There's hardly any leaf fall so the soil isn't very fertile. Lack of rainfall and plant material mean the soil is often dry
• Plant adaptations in hot deserts

  • Small leaves - these ensure that less water is lost from the plant by transpiration because the leaf has a smaller surface area
  • Tap roots - these are long roots (7-10 metres long) that reach deep under the ground to access water supplies. The tap roots are much longer and bigger than the plant which is visible at the surface
  • Spines - some plants have spines instead of leaves, eg cactuses. Spines lose less water than leaves so are very efficient in a hot climate. Spines also prevent animals from eating the plant
  • Waxy skin - some leaves have a thick, waxy skin on their surface. This reduces water loss by transpiration
  • Water storage - some plants, known as succulents, store water in their stems, leaves, roots or even fruits. Plants which store water in their leaves and stems also have a thick waxy skin so that they lose less water by transpiration
• Animal adaptations in hot deserts

  • long eye lashes, hairy ears and closing nostrils help to keep out sand
  • thick eyebrows which stand out and shade eyes from the sun
  • wide feet so they don't sink in the sand
  • they can go without water for over a week because they can drink gallons in one go
  • they can go months without food - they store fat in their humps
  • body temperature can change to avoid losing water through sweating
  • they are well camouflaged
  • thick fur helps to keep them warm at night
• Interdependence


  The biotic (living) parts of hot deserts (plants, animals and people) and the abiotic (non-living) parts (climate, water and soils) are closely related – if one component changes, the others will be affected
• Examples of interdependence in hot deserts

  1. Plants gain their nutrients from the soil and provide nutrients and water to the animals that eat them. In turn, animals spread seeds through their dung which helps plants to reproduce.

  2. The hot and dry climate affects the soil. Soils are low in nutrients because the climate means there is little decomposition of dead plants (because there are much fewer plants to begin with). This makes new plant growth more difficult.

  3. The sparse vegetation limits the amount of food available, so the desert can only support small populations of animals.
• Biodiversity in hot deserts

  • Much lower than biodiversity in other global ecosystems as very few species can survive the extremely dry conditions, extremely hot conditions, and very short periods of rainfall
• Adaptation


  The process of change through which an animal or plant becomes more suited to its environment
• Plants and animals need very specialised adaptations to be able to survive in the extreme conditions of the hot desert
• Describing adaptations


  Outlining what features the species has
• Explaining adaptations


  Saying why the species needs these features to survive in the extreme physical conditions
• Physical conditions of hot deserts include high daytime temperatures of up to 50°C, high diurnal temperature range, less than 250mm rainfall a year, infertile soils less than 1m deep
• Silver ant


  • Has silver armoured skin to reflect intense heat of the sun and tolerate midday temperatures of up to 50°C, which other animals cannot
• Camel


  • Adaptations to be researched and described/explained in relation to hot desert physical conditions
• Kangaroo rat


  • Adaptations to be researched and described/explained in relation to hot desert physical conditions
• Cactus


  • Adaptations to be researched and described/explained in relation to hot desert physical conditions
• Resurrection plant


  • Adaptations to be researched and described/explained in relation to hot desert physical conditions
• Desert soils tend to be sandy or stony, with little organic matter. Desert soils are not very fertile.
• There is not much organic matter because there is little vegetation. The decomposition of vegetation is what creates brown and fertile soils - these are not found in the desert because there isn't much vegetation at all.
• The soils are very dry but they can soak up water rapidly after rainfall.
• The soils are very thin – usually only about 1m deep. Don't be fooled by the up to 100m sand dunes that sit on top of the soils; these are not soils and just cover up the thin, infertile soil layer.
• Desert soils tend to be sandy or stony, with little organic matter. Desert soils are not very fertile. There is not much organic matter because there is little vegetation. The decomposition of vegetation is what creates brown and fertile soils - these are not found in the desert because there isn't much vegetation at all. The soils are very dry but they can soak up water rapidly after rainfall. The soils are very thin – usually only about 1m deep. Don't be fooled by the up to 100m sand dunes that sit on top of the soils; these are not soils and just cover up the thin, infertile soil layer.
• Desertification is the result of both physical processes and human activity
• Main causes of desertification

  • Climate change
  • Population growth
  • Removal of fuel wood
  • Overgrazing
  • Over-cultivation
  • Soil erosion
• All of these causes lead to the removal of vegetation which protects the fragile topsoil. Without this protection soils are very easily eroded by the wind and rain. As this happens the area gradually turns to desert and people are forced to move.
• Environmental refugee


  Someone who is forced to leave their homeland due to sudden or gradual alterations to the natural environment
• Desertification has led to the loss of 650,000km2 of farmland in the Sahel over the past 50 years
• Sahel


  A semi-arid strip of land just south of the Sahara desert
• Sahel


  • 5400km long and 1000km wide
  • Semi-arid land that marks the boundary between the Sahara desert to the north and the tropical grasslands (savannah) biome to the south
  • Many people are able to live in the Sahel because of the occasional rains
  • Life is very difficult because rainfall is irregular and droughts are becoming increasingly common
• Water and soil management

  1. Stone lines

  2. Contours

  3. Reduce runoff
• Water and soil management

  Can prevent desertification by reducing runoff and erosion
• Tree planting


  1. Planting

  2. Soil

  3. Soil Erosion

  4. Nutrients

  5. Decomposers

  6. Overgrazing

  7. Fire Wood
• Tree planting


  Can prevent desertification by stabilizing soils and providing vegetation cover
• Appropriate technology


  Using materials that are freely available, not concrete walls or metal pipes
• Appropriate technology


  • Better charcoal stoves
  • Man powered water pumps
  • Ploughs pulled by cows
• Appropriate technology - solar stoves

  1. Solar energy

  2. Deforestation

  3. Fire wood
• Appropriate technology - solar stoves

  Can prevent desertification by reducing deforestation and reliance on firewood
• A combination of techniques would be best to manage desertification
• Sand dam


  An appropriate technology for the Sahel that stores water in sand