Desert Biomes: KS3 Geography Explained

A desert is any region that receives less than 250 mm of precipitation per year. Deserts cover roughly 33% of Earth's land surface, making them the planet's most extensive terrestrial biome. Far from being lifeless, they support remarkable communities of organisms — and enormous human populations — adapted to extreme water scarcity.

Where are deserts found and what types exist?

Deserts are not all hot and sandy. Geographers classify them into several types based on the mechanism that causes aridity.

Desert type | Definition | Example
Hot desert | High temperatures year-round; below 250 mm rainfall; large daily temperature range | Sahara (Africa), Arabian Desert, Thar Desert (India/Pakistan)
Cold desert | Cold winters; very low precipitation, often falling as snow | Gobi Desert (Central Asia), Patagonian Desert (South America)
Coastal desert | Cold ocean currents chill air and suppress rainfall | Namib Desert (Namibia), Atacama Desert (Chile/Peru)
Rain-shadow desert | Mountain ranges block moisture-bearing winds | Great Basin Desert (USA), Patagonian Desert

The Sahara is the world's largest hot desert at approximately 9.2 million km² — almost the size of the United States. The Antarctic ice sheet is technically the world's largest desert, receiving less than 200 mm of precipitation per year, qualifying it as a polar desert.

Why do deserts form where they do?

Understanding desert formation requires thinking spatially — considering global patterns of air pressure, wind, and ocean currents.

Sub-tropical high-pressure belts: At the Equator, intense heating causes air to rise, cool, and shed its moisture as rainfall. That air descends at roughly 20–30° North and South, warming and drying as it does. This is why the world's major hot deserts — the Sahara, Arabian, Thar, and Australian — lie in a band between 15° and 35° from the Equator.

Rain-shadow effect: Mountain ranges force moist air upward, triggering rainfall on the windward side. Air descending the leeward side is dry and warm. The Great Basin Desert (USA) lies in the rain shadow of the Sierra Nevada.

Continentality: Areas deep in large continental interiors — far from the ocean — receive little moisture. The Gobi Desert is partly explained by its extreme distance from any sea.

Cold ocean currents: Cold currents chill coastal air, suppressing rainfall. The Atacama Desert lies alongside the cold Humboldt Current — some of its weather stations have never recorded rain.

How do plants adapt to desert conditions?

Plants in hot deserts face two main challenges: water scarcity and extreme heat. Three main survival strategies have evolved.

Succulents store water in their tissues. The saguaro cactus of the Sonoran Desert absorbs hundreds of litres after a rainstorm, stored in its pleated trunk. Shallow roots spread widely to capture surface rain quickly. Thick, waxy skin minimises evaporation; spines replace leaves, reducing water loss and deterring herbivores.

Ephemerals (drought-avoiders) complete their entire life cycle — germinating, flowering, setting seed — within weeks of a rare rainstorm. Their seeds lie dormant for years until precise conditions trigger germination. After rains, "super-blooms" of wildflowers can carpet normally bare desert ground.

Deep-rooted xerophytes send tap roots many metres down to reach the water table, sustaining growth during long dry periods.

How do animals adapt to desert conditions?

Desert animals must manage water loss and heat gain, and have evolved both behavioural and physiological adaptations to do so.

Behavioural adaptations are often the most powerful. Many desert mammals and reptiles are nocturnal — active only at night when temperatures fall dramatically. The fennec fox (Sahara) and kangaroo rat (North America) rarely or never need to drink water, obtaining all their moisture from food. During the hottest part of the day, most desert animals shelter underground, in rock crevices, or in shade.

Physiological adaptations: The dromedary camel can tolerate body temperature fluctuations of up to 6°C, reducing the need for sweating. It stores fat in its hump. Reptiles are ectothermic (cold-blooded) — they do not need to metabolise food to maintain body temperature, dramatically reducing food and water requirements. Many desert animals produce highly concentrated urine and dry faeces to minimise water loss.

What is desertification and what causes it?

Desertification is the process by which productive land at the margins of deserts is degraded until it takes on desert characteristics — losing vegetation, soil fertility, and the ability to support agriculture.

Desertification is caused by a combination of natural climate variability and human pressures.

Natural factors: Periods of drought — which are part of the natural climate cycle in semi-arid regions — reduce vegetation cover and expose soil to erosion by wind and rain.

Human factors:

Overgrazing: Livestock eat and trample vegetation faster than it can recover, exposing bare soil.

Overcultivation: Repeated ploughing without adequate rest or fertilisation exhausts soil nutrients.

Deforestation: Removing trees and shrubs destroys root systems that hold soil in place and recycle moisture.

Population pressure: Growing populations in semi-arid regions intensify all of the above pressures.

The Sahel — a band of semi-arid land stretching across Africa south of the Sahara, from Senegal to Eritrea — is the world's most prominent example of desertification. Periods of drought in the 1970s and 1980s, combined with population growth and overgrazing, led to catastrophic land degradation and famine, particularly in Ethiopia and Sudan.

What are the SEEP impacts of desertification?

Applying the SEEP framework gives a systematic view of desertification's consequences.

Social: Communities lose the land they depend on for food and livestock. As land becomes unproductive, people migrate — creating environmental refugees. Women and children in affected areas typically bear the heaviest burden, as they must travel longer distances to find water and firewood. Food insecurity leads to malnutrition, particularly affecting children under five.

Economic: Farmers and pastoralists lose their livelihoods as land becomes unproductive. Countries in the Sahel — already among the world's poorest — face reduced agricultural output, higher food import costs, and greater aid dependence.

Environmental: As vegetation is lost, soils erode — carried away by wind (dust storms) or by rare but intense rainfall. Without plant cover, albedo increases, reducing local rainfall further in a positive feedback loop. Biodiversity falls sharply.

Political: Competition for scarce land and water has contributed to conflict between farming and herding communities. Lake Chad has shrunk by approximately 90% since the 1960s, due to climate change and over-abstraction, undermining livelihoods across four countries. The Great Green Wall initiative — planting trees across the Sahel from Senegal to Djibouti — is an international response, though progress has been uneven.

Frequently asked questions

Are all deserts hot?

No. The definition of a desert is based on precipitation, not temperature: any area receiving less than 250 mm per year qualifies. Cold deserts, such as the Gobi in Central Asia and the Patagonian Desert in South America, experience freezing winters and relatively cool summers. Antarctica is the world's largest desert by area. The distinction matters geographically because the processes that create cold deserts (continentality, rain-shadow) differ from those creating hot deserts (sub-tropical high-pressure belts, cold ocean currents).

What is the difference between aridity and desertification?

Aridity is a permanent climatic condition — a desert is simply a region where evaporation consistently exceeds precipitation. Desertification, by contrast, is a process of land degradation: previously productive land at the margins of deserts being degraded by the combination of drought and human pressure. Not all arid land is desertified, and desertification does not necessarily mean a region permanently becomes a desert — land can sometimes be rehabilitated through careful water management, reforestation, and reduced grazing pressure.

How does the SEEP framework help you answer exam questions about deserts?

The SEEP lens (Social, Economic, Environmental, Political) ensures you cover all dimensions of an issue rather than just listing facts. Structuring an answer around SEEP shows the examiner you are thinking geographically across different scales. Social impacts include food insecurity and migration; economic impacts include loss of livelihoods; environmental impacts include soil erosion and biodiversity loss; political impacts include conflict over scarce resources. SEEP prevents tunnel vision — describing only environmental impacts while forgetting people.

Why is the Sahel particularly vulnerable to desertification?

The Sahel sits at the ecological margin between the Sahara Desert to the north and the wetter savannah to the south. Rainfall is low, seasonal, and highly variable from year to year — communities cannot rely on consistent agricultural output. The region has high population growth rates, which increase pressure on land resources. Poverty limits the ability of farmers to invest in soil conservation or irrigation. Climate change is projected to intensify drought frequency and severity across the Sahel. These factors combine to make the Sahel one of the world's most environmentally and humanly vulnerable regions.

For spatial thinking and SEEP analysis of desert environments — explore KS3 geography support at aitutors.me.