AQA A-level Geography · 3.1.2

Hot desert environments and aridity

50 exam-style questions with answers for 3.1.2 Hot desert environments and aridity in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.1.2.1 · Desert systems
Explain how a hot desert can be viewed as a system. [4 marks]
Answer:
Inputs include insolation, wind-blown sediment and occasional rainfall or runoff (1); stores include sand dunes, weathered rock debris (regolith) and groundwater (1); flows include wind and water transporting sediment (1); outputs include sediment blown or washed out of the system and evaporation (1).
Question 2 · Spec 3.1.2.1 · Desert systems
Distinguish between a landform and a landscape. [2 marks]
Answer:
A landform is an individual feature such as a barchan dune or a wadi (1); a landscape is the overall appearance of an area, made up of related landforms that combine, such as a sand sea or a pediment landscape (1).
Question 3 · Spec 3.1.2.1 · Desert systems
Explain how a desert sand dune system can be in dynamic equilibrium. [2 marks]
Answer:
Sand input by wind is balanced by sand output on average (1); dunes may migrate, but their overall form is maintained over time (1).
Question 4 · Spec 3.1.2.1 · Desert systems
Explain how vegetation can create positive feedback on a sand dune. [2 marks]
Answer:
Plants colonising the dune trap sand and their roots bind it (1); the dune becomes more stable, allowing more vegetation to grow and further stabilisation (1).
Question 5 · Spec 3.1.2.1 · Global distribution
Describe the global distribution of hot deserts. [3 marks]
Answer:
They lie mainly between about 15° and 35° north and south of the equator (1); often on the western sides of continents or in continental interiors (1); examples include the Sahara, Arabian, Thar, Kalahari, Namib, Atacama and Australian deserts (1).
Question 6 · Spec 3.1.2.1 · Global distribution
Distinguish between arid and semi-arid areas. [2 marks]
Answer:
Arid areas have very low rainfall, usually under about 250 mm a year (1); semi-arid areas have somewhat higher rainfall, around 250 to 500 mm, with a short wet season (1).
Question 7 · Spec 3.1.2.1 · Global distribution
What are desert margins? Give an example. [2 marks]
Answer:
The transitional zones between deserts and more humid areas (1); for example the Sahel on the southern edge of the Sahara (1).
Question 8 · Spec 3.1.2.1 · Global distribution
Distinguish between mid-latitude and low-latitude deserts. [2 marks]
Answer:
Low-latitude deserts such as the Sahara are hot all year (1); mid-latitude deserts such as the Gobi are in continental interiors or rain shadows and have cold winters (1).
Question 9 · Spec 3.1.2.1 · Climate
Describe the characteristic climate of hot deserts. [4 marks]
Answer:
Any four from: very high daytime temperatures, often over 40 °C (1); large diurnal temperature range (1); low annual rainfall, usually under 250 mm (1); rainfall that is unreliable and often intense (1); very high evaporation rates (1); low humidity and clear skies (1).
Question 10 · Spec 3.1.2.1 · Climate
Explain the large diurnal temperature range in hot deserts. [3 marks]
Answer:
Clear skies and dry air allow intense insolation by day (1); at night heat is lost rapidly by radiation (1); there is little cloud, vegetation or moisture to retain heat (1).
Question 11 · Spec 3.1.2.1 · Climate
Explain why rainfall in hot deserts is unreliable and often intense. [3 marks]
Answer:
Rain depends on rare convective storms or the shifting edges of rain-bearing systems (1); intense surface heating can produce brief heavy downpours (1); the year-to-year variation is large, and dry ground cannot absorb the rainfall, causing flash floods (1).
Question 12 · Spec 3.1.2.1 · Climate
Define insolation. [1 mark]
Answer:
Incoming solar radiation reaching the Earth's surface.
Question 13 · Spec 3.1.2.1 · Climate
Explain why insolation is very high in hot deserts. [2 marks]
Answer:
Clear skies allow most solar radiation to reach the surface (1); the low latitudes mean the Sun is high in the sky and there is little vegetation or water to absorb energy (1).
Question 14 · Spec 3.1.2.1 · Climate
A desert station has a maximum temperature of 42 °C and a minimum of 6 °C in one day. Calculate the diurnal range. [1 mark]
Answer:
36 °C.
Question 15 · Spec 3.1.2.1 · Climate
A desert station records annual rainfall of 90, 120, 60, 95 and 35 mm over five years. Calculate the mean and the range. [3 marks]
Answer:
Total = 400 mm (1); mean = 80 mm (1); range = 120 − 35 = 85 mm (1).
Question 16 · Spec 3.1.2.1 · Soils
Describe the characteristics of desert soils. [3 marks]
Answer:
Thin, coarse (sandy or stony) soils (1); low organic matter because little vegetation supplies litter (1); often salty, with low water-holding capacity and little profile development (1).
Question 17 · Spec 3.1.2.1 · Soils
Explain why salinisation occurs in desert soils. [2 marks]
Answer:
High evaporation draws water to the surface by capillary action (1); the water evaporates and leaves dissolved salts behind, forming a salt crust (1).
Question 18 · Spec 3.1.2.1 · Soils
Explain why desert soils are infertile. [2 marks]
Answer:
Little organic matter and few soil organisms, because plant growth is sparse (1); weak leaching and high salt content, with little water to dissolve and release nutrients (1).
Question 19 · Spec 3.1.2.1 · Soils
Name three types of desert surface. [3 marks]
Answer:
Erg, a sandy desert or sand sea (1); reg, a stony desert covered in gravel (1); hamada, a rocky desert plateau with bare rock (1).
Question 20 · Spec 3.1.2.1 · Vegetation
Define a xerophyte. [1 mark]
Answer:
A plant adapted to survive in very dry conditions.
Question 21 · Spec 3.1.2.1 · Vegetation
Describe four ways in which xerophytic plants are adapted to aridity. [4 marks]
Answer:
Any four from: long taproots reach deep groundwater (1); shallow widespread roots absorb rain quickly (1); a waxy cuticle reduces water loss (1); small leaves or spines reduce transpiration (1); succulent tissue stores water (1); stomata that open mainly at night (1).
Question 22 · Spec 3.1.2.1 · Vegetation
Explain how ephemeral plants cope with aridity. [2 marks]
Answer:
Seeds lie dormant for long periods until rain falls (1); the plants then germinate, flower and set seed in a few weeks before the soil dries (1).
Question 23 · Spec 3.1.2.1 · Vegetation
What are phreatophytes? [1 mark]
Answer:
Deep-rooted plants that obtain water from the water table or groundwater.
Question 24 · Spec 3.1.2.1 · Vegetation
Explain why desert vegetation is often widely spaced. [2 marks]
Answer:
Plants compete for scarce water and nutrients (1); widely spreading roots take water from a large area, so neighbouring plants cannot survive close together (1).
Question 25 · Spec 3.1.2.1 · Vegetation
Describe two ways in which desert animals are adapted to aridity. [2 marks]
Answer:
Any two from: nocturnal behaviour avoids daytime heat (1); burrowing gives cooler shelter (1); concentrated urine and dry faeces reduce water loss (1); large ears help to lose heat (1); some store fat or water (1).
Question 26 · Spec 3.1.2.1 · Interactions
Explain the interactions between climate, soil and vegetation in hot deserts. [3 marks]
Answer:
Low rainfall limits plant growth, giving sparse vegetation cover (1); little organic matter produces thin, infertile soils that hold little water (1); with so little plant cover, runoff and erosion increase, which reduces vegetation further (1).
Question 27 · Spec 3.1.2.1 · Water balance
Define the aridity index. [2 marks]
Answer:
The ratio of annual precipitation to potential evapotranspiration (P ÷ PET) (1); the lower the value, the drier the climate (1).
Question 28 · Spec 3.1.2.1 · Water balance
An area has annual precipitation of 100 mm and potential evapotranspiration of 2,000 mm. Calculate its aridity index. [2 marks]
Answer:
Aridity index = 100 ÷ 2,000 (1); = 0.05 (1).
Question 29 · Spec 3.1.2.1 · Water balance
An area has an aridity index of 0.15. Using the UNEP classification (hyper-arid below 0.05, arid 0.05 to 0.20, semi-arid 0.20 to 0.50), classify it. [1 mark]
Answer:
Arid.
Question 30 · Spec 3.1.2.1 · Water balance
Describe the water balance of a hot desert. [2 marks]
Answer:
Potential evapotranspiration is far greater than precipitation (1); so there is a permanent soil moisture deficit and very little runoff or groundwater recharge (1).
Question 31 · Spec 3.1.2.1 · Water balance
Distinguish between aridity and drought. [2 marks]
Answer:
Aridity is a permanent climatic condition of low rainfall relative to evaporation (1); drought is a temporary period of below-average rainfall in a region that usually has more (1).
Question 32 · Spec 3.1.2.1 · Causes of aridity
Explain how subtropical high pressure causes aridity. [4 marks]
Answer:
Air rises at the equator and moves towards the poles at high altitude (1); it cools and descends at about 30° north and south (1); descending air warms and its relative humidity falls, so cloud does not form (1); this creates stable high pressure with clear skies and little rain (1).
Question 33 · Spec 3.1.2.1 · Causes of aridity
Explain how continentality causes aridity. [2 marks]
Answer:
Areas far from the sea receive little moisture-laden air (1); air crossing land loses its moisture as rain on the way, so interiors such as the Gobi are dry (1).
Question 34 · Spec 3.1.2.1 · Causes of aridity
Explain how relief can cause aridity. [3 marks]
Answer:
Moist air is forced to rise over mountains and drops its rain on the windward side (1); air descends on the leeward side, warming and drying (1); this rain shadow creates desert, as in Patagonia east of the Andes (1).
Question 35 · Spec 3.1.2.1 · Causes of aridity
Explain how cold ocean currents cause aridity. [3 marks]
Answer:
A cold current cools the air above it (1); the cooled, stable air does not rise and form rain clouds, and evaporation from the sea is low (1); coastal deserts such as the Atacama (Humboldt Current) and Namib (Benguela Current) result, with fog but little rain (1).
Question 36 · Spec 3.1.2.1 · Causes of aridity
Explain how prevailing winds can contribute to aridity. [2 marks]
Answer:
Winds blowing from the land to the sea (offshore winds) bring dry air (1); for example the trade winds blowing across the Sahara carry little moisture (1).
Question 37 · Spec 3.1.2.1 · Causes of aridity
Explain why the Atacama is one of the driest places on Earth. [4 marks]
Answer:
The cold Humboldt Current cools and stabilises coastal air (1); the Andes create a rain shadow, blocking moist air from the east (1); subtropical high pressure brings descending air (1); winds are offshore or parallel to the coast, so little moisture is carried inland (1).
Question 38 · Spec 3.1.2.1 · Causes of aridity
Explain why the Namib has frequent fog but very little rain. [2 marks]
Answer:
Warm air moving over the cold Benguela Current is cooled to its dew point, forming fog (1); the cooled air is stable and does not rise to produce rain clouds (1).
Question 39 · Spec 3.1.2.1 · Causes of aridity
Suggest why many hot deserts are found on the western sides of continents. [2 marks]
Answer:
Cold ocean currents flow along these coasts, cooling and stabilising the air (1); prevailing trade winds blow from land to sea (1).
Question 40 · Spec 3.1.2.1 · Causes of aridity
Explain why rainfall in the Sahel is variable from year to year. [2 marks]
Answer:
Rainfall depends on the northward movement of the ITCZ in summer (1); if the ITCZ does not move as far north, the wet season is shorter or fails (1).
Question 41 · Spec 3.1.2.1 · Human use
Suggest why hot deserts are challenging for human habitation. [3 marks]
Answer:
Water is scarce and unreliable (1); extreme heat and large temperature ranges make living and working difficult (1); thin infertile soils limit farming and settlements are remote (1).
Question 42 · Spec 3.1.2.1 · Human use
Describe opportunities for development in hot deserts. [2 marks]
Answer:
Any two from: mineral and oil reserves (1); solar energy from intense insolation (1); irrigated agriculture where groundwater is available (1); tourism based on landscapes and culture (1).
Question 43 · Spec 3.1.2.1 · Human use
Explain why groundwater is a vital resource in hot deserts. [2 marks]
Answer:
Surface water is scarce and rainfall is unreliable (1); aquifers store water from past wetter periods or distant recharge that can be used for drinking and irrigation (1).
Question 44 · Spec 3.1.2.1 · Desert systems
Name the inputs of energy to a hot desert system. [2 marks]
Answer:
Insolation from the Sun (1); wind energy and the energy of occasional runoff (1).
Question 45 · Spec 3.1.2.1 · Water balance
Explain why potential evapotranspiration is much greater than precipitation in hot deserts. [2 marks]
Answer:
High temperatures, intense insolation and low humidity give a very high evaporation demand (1); precipitation is low, so there is not enough water to meet this demand (1).
Question 46 · Spec 3.1.2.1 · Vegetation
Explain why many desert plants are adapted to store water. [2 marks]
Answer:
Rain is infrequent, so water must be held for long dry periods (1); succulent stems or leaves store water in tissue to use between rainfalls (1).
Question 47 · Spec 3.1.2.1 · Climate
Explain why relative humidity is low in hot deserts. [2 marks]
Answer:
Subtropical high pressure brings dry, descending air (1); the air is also very warm and there is little surface water or vegetation to add moisture (1).
Question 48 · Spec 3.1.2.1 · Global distribution
Name three hot deserts and state the continent of each. [3 marks]
Answer:
Any three from: Sahara, Africa (1); Namib or Kalahari, Africa (1); Arabian Desert, Asia (1); Thar Desert, Asia (1); Atacama, South America (1); Mojave or Sonoran, North America (1); Great Victoria or Simpson Desert, Australia (1).
Question 49 · Spec 3.1.2.1 · Global distribution
Explain why the Gobi Desert has very cold winters. [2 marks]
Answer:
It lies in the interior of Asia, far from the moderating effect of the sea (1); it is at high latitude and altitude, and cold air masses from Siberia reach it in winter (1).
Question 50 · Spec 3.1.2.1 · Vegetation
Explain how fog and dew can support life in coastal deserts. [2 marks]
Answer:
Fog and dew condense onto plant surfaces and the bodies of insects, providing moisture where rain is rare (1); some plants and animals, such as Namib beetles, are adapted to collect and drink this water (1).

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