GCSEGeographyAQARevision Notes2. The Living World2.3 Hot Deserts2.3.1 Hot Desert Ecosystem

Hot Desert Ecosystem (AQA GCSE Geography)

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Characteristics of Hot Desert

distribution-of-hot-deserts

Distribution of hot desert climates

  • Hot desert biomes are mostly found in a band around the Tropic of Cancer and Tropic of Capricorn
  • Approximately 20% of the Earth's surface is covered by hot desert ecosystems including in the following areas:
    • North America: The Mojave and Sonoran Deserts of the USA and Mexico
    • South America: The Sechura Desert in Peru and the Atacama Desert in Chile
    • Africa: The Sahara, Kalahari, Namib and Somali Deserts
    • Middle East: The Arabian Desert 
    • Asia: The Dasht-e Lut in Iran, the Gobi, Turkestan, Thar and Taklamakan Deserts
    • Oceania: The Australian Deserts such as the Simpson and Great Victorian deserts

Hot desert characteristics

Characteristics of Hot Desert Regions

Characteristics Hot Desert
Location
  • 15° - 30° north and south of the equator (tropical and sub-tropical)
  • North Africa - Sahara, Southern Africa - Kalahari and Namib, Australia. Middle East
Annual Precipitation
  • Below 250mm
  • When rainfall does occur, it is often short torrential downpours
Temperature Range
  • Daytime temperatures can reach 50°C but average around 25°C
  • Night-time temperatures below 0°C
  • Diurnal range is large up to 45°C
  • Annual range is around 15°C
Seasons
  • Summer and winter
Humidity
  • Low often between 10-30%
Soils
  • Tend to be saline - evaporation draws salts to the surface (salinisation)
  • Thin, sandy, grey and rocky 
  • Contain little organic matter
  • Not very fertile
Biodiversity
  • Low biodiversity - 5000-6000 plant species, many invertebrates and up to 20 species of bird
  • Plants include cacti, yucca
  • Animals include spiders, scorpions, camels, lizards

climate-graph-for-jeddah-saudi-arabia

An example of a climate graph for a typical hot desert region

Factors influencing the hot desert climate

  • High pressure all year which means the air is descending and warming so precipitation does not occur because the air is not rising
  • Prevailing winds are often from over land masses which means they contain little moisture
  • Some deserts are in a rain shadow so there is little rainfall
  • Cold ocean currents on the west side of continents may reduce summer temperatures due to the cooling effect of the ocean

Influence of pressure systems

  • Hot deserts form between 15°- 30° north and south of the equator as a result of the atmospheric pressure systems
    • Air rises at the equator and when it reaches the upper atmosphere it moves north and south
    • The air cools and starts to sink
    • This creates a zone of high pressure at about 30° north and south of the equator
    • Due to the sinking air, warm air cannot rise, condense and form clouds, resulting in high aridity

atmospheric-pressure-systems

The atmospheric pressure system of hot desert biomes

Humans 

  • The edges of the desert are used for livestock herding
  • Communities such as the Bedouin are nomadic
    • Live in large open tents made from fabric woven from camel hair and vegetable fibres
    • Food sources are mainly from the animals that the Bedouin herd - goats and cattle
    • Headwear is worn to protect against the heat of the sun and sand
  • Restrictions on movements due to international borders have affected the Bedouin lifestyle
  • Many Bedouin are no longer nomadic and live in permanent settlements

Interdependence in a Hot Desert

  • All parts of the hot desert ecosystem are interdependent
    • A change in one part affects the others

Nutrient cycle

  • The growth of plants is limited due to the extremes of temperature and lack of water
  • The nutrient cycle is very slow
  • Most nutrients are stored in the soil

desert-nutrient-cycle

Nutrient cycling of hot desert biomes

  • Due to a lack of organic matter the soils are coarse, sandy and low in nutrients

Plant & Animal Adaptations

Adaptations

  • To be able to survive the extreme temperatures and lack of rainfall the plants and animals are extremely well adapted

Adaptations of Plants and Animals in Hot Desert Ecosystems

Plants Animals
Low growing - this helps to avoid water loss due to strong winds Camels have a range of adaptations including two sets of eyelashes and nostrils which close to keep sand out of their ears and noses. They also store fat in their humps so they can survive for long periods without food or water
Thick stems - used to store water Fennec Fox - have large ears which help them to lose heat
Shallow roots - these spread out near the surface to catch whatever rain falls Burrowing - many animals burrow to avoid the intense day time heat
Long roots - some plants have long tap roots instead of shallow roots to reach water deep underground Insects and reptiles have waterproof skin to reduce water loss
Small leaves or needles - the smaller surface area reduces water loss Nocturnal - some animals hunt at night to avoid the daytime heat

Worked example

Study Figure 1,

fig-9-june-2019-paper1-qp-gcse-aqa-geo

Plants and animals adapt in order to survive in a hostile environment.’ 

Explain this statement. Use either Figure 1 and your own understanding.

[6 marks]

  • The command word “explain” is used, which means to provide an account of the ways that animals and plants adapt to a hot desert
  • You need to give examples for both plants and animals and then explain them
  • It is not enough to say 'spines instead of leaves' you need to explain how this helps the plant survive 
  • In a level 2 and 3 answer you are expected to use geographical terms and include both examples of plant and animal adaptations
  • You should include examples from your own understanding as well as from figure 1.

  • An example of an answer for each level can be seen below
    • These are just examples and there are many others which can be found in the mark scheme - see topic question 2

Answer:

Level  Marks Exemplar Answer

1 

(Basic)

 1-2 Cacti have spines instead of leaves and have thick stems. Camels have two sets of eyelashes and a hump to store fat.

2

(Clear)

 3-4 The hot desert has low rainfall and high temperatures. Cacti are adapted to this by having spines instead of leaves which reduce water loss. Camels are adapted by having two sets of eyelashes which keep out the sand.

3 

(Detailed)

 5-6 The hot desert has less than 250mm of rainfall a year, daytime temperatures can reach 50oC and night time temperatures fall as low as 0oC. To survive cacti have spines instead of leaves and a thick waxy coating which helps to reduce water loss. Other plants grow very slowly which requires less energy such as the welwitschia . Camels are adapted in a variety of ways including two sets of eyelashes and nostrils they can close to help keep out sand. Other animals are adapted by having large ears which give off heat such as the Fennec Fox.

Biodiversity Issues

  • Low levels of precipitation and high temperatures in many areas of hot deserts lead to low biodiversity
  • Where water is available there are higher levels of biodiversity
  • When rainfall does occur in desert areas a desert bloom may follow
    • Seeds and bulbs which have laid dormant germinate 
    • In the Atacama Desert desert blooms may occur between September and November when rainfall is unusually high
    • This can lead to over 200 species of flowers blooming, attracting insects and lizards
  • Threats to hot desert biodiversity are mainly human activities including:
    • Mining
    • Climate Change
    • Fuelwood gathering

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    Bridgette

    Author: Bridgette

    After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.