5 minute read
Desertifi cation
ENVIRONMENT
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How deserts grow
Discover why farmland across the planet is being swallowed at a terrifying rate by creeping sands…
Each year 0.2 per cent of usable farmland is lost from arid regions worldwide. That may not sound like a lot, but pressure on food and water resources is growing exponentially. Indeed, Earth’s population is predicted to increase by a staggering 4 billion people by 2100.
Desertifi cation occurs when farmland is overused in dry climates with fragile ecosystems already vulnerable to drought. Many affected areas are home to the poorest people in the world.
Livestock overgraze grass and wear away earth with their hooves, while intensive arable farming depletes nutrients in the soil. Toxic salts build up and farmland becomes waterlogged when fi elds are overwatered by irrigation. Water and wind make the problem even worse by removing nutrient-rich soil, gradually leaving nothing but a bare desert behind.
No continent is immune from desertifi cation. Around a third of our planet is directly affected and population pressure is typically the root cause of it.
Land degradation is not a new problem, though. Studies suggest the collapse of the Mayan civilisation in 900 CE was triggered by population growth followed by crop cultivation on steep slopes with fragile soil.
Desertifi cation has devastating effects on people and the environment alike. Farmers face famine or the threat of disease if they migrate away from depleted farmland. Dust from the affected land can also cause lung diseases. In China, sandstorms and dunes from the advancing Gobi Desert swallow up entire villages and affect air quality in Beijing some 80 kilometres (50 miles) away.
In Africa’s Sahel, desertifi cation increases drought risk too; vegetation dying back exposes the pale sand, which refl ects more heat, reducing updraughts of damp air that generate clouds and rain, so once it begins, desertifi cation is self-propagating.
Farmland to wasteland
See how intensive agriculture can transform a fertile landscape into a barren terrain
Virgin forest
Around six per cent of the world’s forests are in arid lands where they hold soil in place, replenish ground water and are thought to also encourage rainfall.
Nutrient loss
When crops are harvested, nutrients are stripped from the earth. Unless fertilisers are added, the farmland becomes barren and degraded.
Deforestation Heavy machinery
Intensive ploughing loosens the topsoil, creating a dry powder, less capable of holding water, susceptible to drought and easily washed or blown away.
Trees are cut down to graze livestock or plant crops. The forest recovers slowly due to the limited water supply.
1The ancient Rapa Nui who built approximately 900 giant hollow-eyed Moai statues – some weighing 75 tons – may have collapsed after stripping the island of palm forest.
DID YOU KNOW?
A single millimetre (0.04in) of soil can take hundreds of years to form in dry climates
The Aral Sea is an extreme example of desertifi cation, where the water has receded so much that many ships now sit rusting miles away from the once-huge lake
Desert expansion around the globe
What places on Earth have been most affected by desertifi cation?
Vulnerability Other regions
Very high High Moderate Low Dry Cold Humid not vulnerable
Aral Sea
This giant lake began shrinking in the Sixties when water was diverted to grow cotton. Today it holds ten per cent of its original volume.
Gobi Desert
Around 3,600km2 (1,400mi2) of China becomes desert each year, due to the expansion of the Gobi. Causes include overcultivation and population pressure on water and soil.
Over-farming
Cultivated land is used for many years to grow the same crops. In less intensive agriculture, farmland is left idle some seasons to allow the soil to recover.
Great Plains
The US Great Plains turned into a ‘dust bowl’ when wheat production expanded after WWI. Improved farming methods helped the Plains recover, but they remain vulnerable to desertifi cation.
Sahel region
Approximately 40 per cent of Africa is affected by desertifi cation. Population growth of three to four per cent a year and extreme poverty leads to overgrazing, overfarming and drought.
Australia
An estimated 42 per cent of Australia is affected by desertifi cation. The main cause is overgrazing by sheep and cattle introduced by European settlers.
Vegetation loss
As the soil becomes saltier and loose nutrient-rich topsoil is removed, plants struggle to grow. The ground is exposed to further action by wind and water.
Irrigation
Around 60 per cent of irrigated farmland is in drylands. When water is added to the soil, it evaporates, leaving salt behind. Salt also rises to the surface when farmland becomes waterlogged.
Desert land
At this point farmers are forced to abandon their fi elds. What was once cultivated land resembles a desert – dusty, salty and unable to support most plant and animals.
How can we fi ght desertifi cation?
Reversing desertifi cation depends on tackling human exploitation of land by providing sources of income. Imagine a wall of trees and shrubs – 8,000 kilometres (5,000 miles) long and 15 kilometres (nine miles) wide – snaking west to east across Africa. The Great Green Wall project began in 2011 to counter desertifi cation on the Sahara Desert fringe. Since then, 12 million drought-resistant acacia trees have been planted in Senegal alone.
Large-scale planting schemes were used to tackle desertifi cation in 1935 during the US Dust Bowl too. China initiated its own green-wall project in 1978, which afforested 9 million hectares (22.2 million acres) in the fi rst ten years.
Large forested areas replenish the water table, act as wind breaks to stop sand dunes in their tracks, and may increase rainfall; for example, an estimated 60 per cent of Amazon rainfall is created by the rainforest itself. Advocates of the African green wall believe it can even counter terrorism, providing jobs by producing gum arabic from acacia.
Other techniques to fi ght desertifi cation include improving irrigation techniques, applying bacteria to dunes and introducing sand fences and pools.
