Deserts as Natural Systems (AQA A Level Geography)
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The image shows major global deserts. Identify the deserts labelled 1 to 5.
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The image shows major global deserts. Identify the deserts labelled 1 to 5.
The deserts are:
Mojave
Atacama
Sahara
Namib
Gobi
Describe the global distribution of arid and semi-arid regions.
Arid areas are located along the mid- and low-latitudes of the Tropic of Cancer and the Tropic of Capricorn.
Semi-arid areas lie along the margins of these arid areas; for example, the Sahara desert is an arid area and the Sahel would be classified as a semi-arid area.
Areas are also located adjacent to mountain ranges, like the Atacama Desert, which is alongside the Andes.
True or False?
Deserts are defined as areas that receive less than 250mm of precipitation per annum.
True.
Deserts are defined as areas that receive less than 250mm of precipitation per annum.
Define the term aridity.
Aridity is the degree to which a climate lacks moisture or is extremely dry.
What does NPP mean?
NPP means net primary production, which is the amount of organic matter produced by plants in an ecosystem.
State the meaning of dynamic equilibrium.
Dynamic equilibrium is a state in which opposing forces or processes are balanced, resulting in a stable system.
What is a hamada desert?
Hamada is a type of desert landscape where most of the sand has been removed, leaving behind a surface of gravel, boulders and bare rock plateaus.
True or False?
Erg deserts cover about 70% of desert landscapes.
False.
Erg (sandy) deserts are common in only about 30% of deserts.
What is a reg desert?
A reg desert is a desert landscape characterised by hard, impermeable surfaces composed of rock fragments set in sand or clay.
What are ephemerals?
Ephemerals are plants with short life cycles that flower quickly after rain, produce seeds, and die back during dry periods.
Why is soil the largest store of nutrients in deserts?
Desert soil stores the most nutrients because low precipitation rates prevent leaching.
What is the diurnal temperature range in desert regions?
The diurnal temperature range in desert regions can be up to 30 °C.
Define the term xerophyte.
A xerophyte is a plant adapted to survive in environments with little water.
True or False?
Deserts have high biomass.
False.
Deserts generally have low biomass, with only about 500 kg per hectare compared to 250 000 kg per hectare in rainforests.
What are halophytes?
Halophytes are salt-tolerant plants that can grow in saline environments.
Define the term aridisol.
Aridisol is a type of soil found in arid regions, characterised by low moisture content and little organic matter.
What is deflocculation?
Deflocculation is the dispersal of soil particles due to high concentrations of sodium salts, causing the soil to become impermeable.
True or False?
Desert soils are typically deep and fine-textured.
False.
Desert soils are typically dry, shallow, and coarse-textured.
What is a duricrust?
A duricrust is a hard rock band at or below the surface of desert soils that makes root development in plants difficult.
Define the term phreatophyte.
A phreatophyte is a deep-rooted plant that obtains water from the water table or the layer of soil just above it.
What is calcrete?
Calcrete is a type of duricrust formed from calcium carbonate, found mainly in semi-arid regions.
Define pyrophyte.
A pyrophyte is a plant that has adapted to tolerate fire, either by resisting its effects or by needing fire for reproduction.
What are the five main causes of aridity?
The five main causes of aridity are:
global circulation of air.
topography/rainshadow effect.
cold ocean currents.
prevailing winds.
continentality.
What is the Hadley cell?
A Hadley Cell is a large convective cell in the atmosphere that controls air circulation between the equator and the tropics in both hemispheres.
What is the ITCZ?
The ITCZ (Intertropical Convergence Zone) is a low-pressure zone near the equator where the Northeast and Southeast Trade Winds meet.
True or False?
The aridity index is based on the relationship between precipitation and potential evapotranspiration.
True.
The aridity index is based on the relationship between precipitation (P) and potential evapotranspiration (PET).
What is the P/PET ratio for arid regions?
The P/PET ratio for arid regions is less than 0.20, meaning precipitation supplies less than 20% of the water needed for optimum plant growth.
What does rainfall effectiveness mean?
Rainfall effectiveness is the amount of water that reaches the root zone and is available to plants.
What is an orographic effect?
The orographic effect, also known as the rainshadow effect, occurs when air is forced to rise over mountains, cooling and releasing moisture on one side, leaving dry air on the other side.
Define continentality in the context of aridity.
Continentality in the context of aridity refers to the effect of being located in the middle of a continent, far from moisture-bearing winds, which increases aridity.
What does PET stand for in the context of water balance?
PET stands for Potential Evapotranspiration, which is the amount of evaporation and transpiration that would occur if sufficient water were available.
True or False?
In most deserts, potential evapotranspiration exceeds precipitation.
True.
In most deserts, potential evapotranspiration (PET) exceeds precipitation (P).