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Hot deserts are some of the most extreme environments on Earth. Despite their harsh conditions, they cover approximately one-third of the world's land surface. For AQA GCSE Geography, you need to understand where hot deserts are found, what their climate is like, and the characteristics of their soil, vegetation, and landscape. This lesson covers the physical geography of hot deserts in detail.
Hot deserts are found in two main bands around the world, at approximately 30°N and 30°S of the Equator — the Tropics of Cancer and Capricorn.
| Desert | Location | Area (approx.) | Countries |
|---|---|---|---|
| Sahara | North Africa | 9.2 million km² | Algeria, Libya, Egypt, Morocco, Chad, and others |
| Arabian | Middle East | 2.3 million km² | Saudi Arabia, Yemen, Oman, UAE |
| Thar | South Asia | 200,000 km² | India (Rajasthan), Pakistan |
| Mojave / Sonoran | North America | 310,000 km² combined | USA (California, Arizona, Nevada), Mexico |
| Kalahari / Namib | Southern Africa | 930,000 km² combined | Botswana, Namibia, South Africa |
| Great Sandy / Gibson | Australia | 650,000 km² combined | Australia (Western Australia, Northern Territory) |
The location of hot deserts is explained by global atmospheric circulation, specifically the Hadley Cell:
Some deserts are also dry because of:
Exam Tip: The link between the Hadley Cell, sinking air at 30°, high pressure, and aridity is a fundamental explanation. Learn it as a sequence and you can use it in any question about desert distribution.
Hot deserts have an extreme climate characterised by high temperatures and very low rainfall.
| Climate Feature | Detail |
|---|---|
| Annual rainfall | Less than 250 mm per year; some areas receive less than 25 mm |
| Daytime temperature | Commonly 40–50°C; the record is 56.7°C (Death Valley, USA) |
| Night-time temperature | Can drop to below 0°C in winter |
| Daily temperature range | Very large — often 30–40°C difference between day and night |
| Cloud cover | Very low — clear skies most of the year |
| Humidity | Very low — often below 20% |
| Wind | Strong, dry winds are common; they drive sand and dust storms |
During the day, the intense solar radiation heats the ground rapidly because there is no cloud cover to reflect sunlight and no vegetation to provide shade. At night, the heat escapes quickly because:
This produces the dramatic diurnal (daily) temperature range that defines hot desert climates.
Exam Tip: The extreme diurnal temperature range is a key characteristic. Always explain why it occurs (lack of cloud cover and moisture) rather than simply stating that it exists.
Desert soils are generally poor and poorly developed:
| Soil Feature | Detail |
|---|---|
| Type | Aridisol — dry, often sandy or stony |
| Depth | Shallow in many areas; deeper in sand dune regions |
| Fertility | Low — very little organic matter due to sparse vegetation |
| Colour | Pale yellow, grey, or reddish |
| Water content | Extremely low; moisture evaporates very quickly |
| Salt content | Often high — evaporation draws salts to the surface (salinisation) |
In some areas, a hard, cement-like layer called caliche or duricrust forms at or near the surface where minerals have been deposited by evaporating water.
Hot deserts are not just endless sand dunes. In fact, only about 25% of the world's deserts are covered in sand (called erg). The rest consists of:
| Landscape Type | Description | Example |
|---|---|---|
| Erg | Sand seas — vast areas of wind-blown sand dunes | Grand Erg Oriental (Sahara) |
| Reg | Stony desert — flat plains covered with gravel and pebbles | Reg desert in southern Algeria |
| Hamada | Rocky plateau — bare rock surfaces swept clean by wind erosion | Hamada du Draa (Morocco) |
| Wadi | Dry river valley — only contains water during rare rainfall events | Wadi Rum (Jordan) |
| Mesa and butte | Flat-topped hills created by erosion of surrounding softer rock | Monument Valley (USA) |
| Inselberg | Isolated steep-sided hill rising from a flat plain | Uluru / Ayers Rock (Australia) |
Despite the lack of water, powerful processes shape the desert landscape:
| Process | Description |
|---|---|
| Thermal expansion | Repeated heating and cooling causes rocks to expand and contract, eventually cracking them |
| Freeze-thaw weathering | In deserts with cold nights, water in rock cracks freezes, expands, and shatters the rock |
| Onion-skin weathering | (Exfoliation) The outer layers of rock peel away due to thermal expansion |
| Salt crystallisation | Evaporation draws salt into rock pores; salt crystals grow and break the rock apart |
| Process | Description |
|---|---|
| Wind erosion | Wind picks up and carries sand particles, which blast against rock surfaces (abrasion) |
| Flash floods | Rare but intense rainfall creates sudden, powerful floods that erode channels and carry debris |
Exam Tip: Flash floods are a surprisingly important process in desert geomorphology. Despite the aridity, the lack of vegetation and hard-baked soil mean that when rain does fall, water runs off extremely quickly, causing sudden and powerful erosion.
Although hot deserts receive very little rainfall overall, when it does rain, the effects can be dramatic:
You may be asked to interpret a climate graph for a hot desert location. Key things to identify:
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