What processes shape hot desert landscapes, and how do aridity and human activity drive desertification at the margins?
The global distribution and causes of aridity; sources of energy and sediment; aeolian and water processes; desert landforms; and the causes, impacts and management of desertification.
A focused answer to AQA A-Level Geography 3.1.2, covering the distribution and causes of aridity, energy and sediment sources, aeolian and fluvial processes, desert landforms, and the causes, impacts and management of desertification on desert margins.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
AQA section 3.1.2 wants you to explain the global distribution and causes of aridity, identify the sources of energy and sediment in deserts, describe and explain aeolian and fluvial processes and the landforms they produce, and analyse the causes, impacts and management of desertification on desert margins. The synoptic thread is that deserts are energy-limited by water but shaped by both wind and (surprisingly) water, and that human pressure tips fragile margins into degradation.
Distribution and causes of aridity
Hot deserts cluster around 20 to 30 degrees north and south. Aridity has four reinforcing causes:
- Subtropical high pressure: the descending limbs of the Hadley cell carry warm, dry air that warms further as it sinks, lowering relative humidity and suppressing precipitation. This is the primary control on the Sahara and Arabian deserts.
- Continentality: continental interiors far from oceans receive little moisture-bearing air (the Gobi).
- Rain shadow: mountains force air to rise, cool and drop its moisture on the windward side, leaving the leeward side dry (the Mojave behind the Sierra Nevada).
- Cold ocean currents: air over cold currents is stable and brings little rain, producing coastal deserts such as the Atacama and Namib.
Energy and sediment sources
The energy driving processes comes from intense insolation (a high diurnal temperature range powers mechanical weathering) and wind. Sediment is supplied by weathering (exfoliation through expansion and contraction, thermal fracture and salt weathering), mass movement on slopes, and ephemeral rivers that carry large loads during rare storms. Some desert sand is also imported by wind from distant sources.
Aeolian and fluvial processes and landforms
Aeolian (wind) processes: deflation removes fines; abrasion sandblasts rock close to the ground; transport is by suspension (fine dust), saltation (bouncing sand, the dominant mode) and surface creep. These build desert pavement, ventifacts, yardangs and migrating dunes (barchan, seif and star forms depending on wind regime and sand supply).
Fluvial (water) processes: despite aridity, flash floods and sheet flooding are powerful and episodic agents. They cut steep-sided wadis, deposit alluvial fans and coalescing bajadas at mountain fronts, and leave playas (salt-crusted lake beds) where water evaporates in basins. Slope retreat under combined weathering and wash forms gently sloping pediments and leaves isolated resistant inselbergs.
Desertification
Causes combine physical factors (climate change, declining and variable rainfall, drought) with human pressures (population growth, overgrazing, over-cultivation, deforestation for fuelwood, and poor irrigation causing salinisation). Impacts cascade: falling crop and pasture yields, food insecurity, soil erosion, malnutrition, rural-to-urban migration and, in extreme cases, conflict over remaining resources.
Management blends physical and social approaches: soil and water conservation (terracing, stone bunds, water harvesting), afforestation (the Great Green Wall initiative across the Sahel), drought-resistant and quick-maturing crops, controlled grazing, and appropriate technology that local communities can maintain.
Try this
Q1. State two causes of aridity in hot deserts. [2 marks]
- Cue. Subtropical high pressure (descending Hadley-cell air); plus rain shadow, continentality or cold ocean currents.
Q2. Outline one management strategy for desertification. [2 marks]
- Cue. Afforestation (Great Green Wall) or water harvesting and stone bunds that conserve soil and moisture.
Q3. Explain how flash floods produce desert landforms. [4 marks]
- Cue. Episodic high-energy flow cuts wadis and, as energy falls at the mountain front, deposits alluvial fans and bajadas, with playas forming where water evaporates in basins.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20196 marksExplain how wind processes contribute to the formation of desert landforms.Show worked answer →
A 6 mark "explain" question rewarding a process-to-landform chain (AO1). Wind (aeolian) processes operate effectively in deserts because sparse vegetation leaves sediment exposed, dry and easily moved.
Deflation removes loose fine material, lowering the surface to form deflation hollows and leaving a coarse lag of desert pavement (reg). Abrasion (wind-blown sand sandblasting rock, strongest near the ground where saltation concentrates) undercuts and sculpts ventifacts, yardangs and zeugen. Transport by suspension, saltation and surface creep moves sand, deposited where wind energy falls to build dunes (crescent-shaped barchans where sand is limited and wind is one direction, linear seif dunes where winds come from two directions).
Markers reward linking a named process to a named landform and noting aeolian work is most effective where vegetation and moisture are minimal.
AQA 20229 marksAssess the relative importance of physical and human causes of desertification on desert margins.Show worked answer →
A 9 mark "assess" question (AO1 plus AO2) needing a judgement on relative importance. Set out the physical causes: declining and increasingly variable rainfall, recurrent drought and rising temperatures linked to climate change, which reduce vegetation cover and expose soil (the Sahel droughts of the 1970s and 1980s).
Then the human causes: population growth driving overgrazing, over-cultivation that exhausts soil, deforestation for fuelwood, and poor irrigation causing salinisation. These strip protective vegetation and accelerate soil erosion by wind and water.
Judge that the two are interlinked: physical drought provides the trigger, but human pressure usually amplifies and sustains degradation, so in most Sahel cases human factors are the more controllable and arguably decisive driver, while climate change increasingly dominates the physical side. Markers reward a calibrated, evidenced judgement rather than a list.
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Sources & how we know this
- AQA A-level Geography (7037) specification — AQA (2016)