Desertification 1

Desertification is the degradation of semi-arid land by human activities and change in climate. It is an environmental degradation process which leads to the decline of productive land. A third of land worldwide is at risk from desertification, and 250 million people are already affected. 46% of Africa is at risk from desertification. Desert is encroaching into semi-arid desert margins.

Physical causes of desertification – climatic change
Lower rainfall – in subtropical areas where most semi-arid areas are, surface water and groundwater will be reduced, because it is used up or evaporated. The volume of water for vegetation is reduced, so the vegetation dies. There are fewer plants and trees, so there are fewer roots to anchor the soil. This leads to soil erosion.

Higher temperatures - global surface temperature has risen by 0.6 degrees over the last century and is predicted to continue to rise. As temperatures increase, the rate of evapotranspiration also increases. This dries out soils, lowering surface water levels. Vegetation dies, so there is less root anchorage and more soil erosion.

Human activity – the main cause of desertification
Overgrazing – if the number of animals increases beyond the carrying capacity, over grazing can become a problem. Overgrazing reduces the amount of vegetation, so there is more soil erosion. Trampling by animals compresses and breaks down the structure of soil making erosion more likely.

Population growth – increases pressure on land and more food is needed to meet the growing demand. This leads to further overgrazing, over cultivation, deforestation and irrigation.

Over cultivation – increases in population through high birth rates and immigration means that there is an increased demand for food. Farmers leave behind traditional land use because more land is required to grow crops. Exploitation of the soil leaves it without enough nutrients to support plants, leaving it unproductive. The soil is then easily eroded.

Deforestation – If population rises, there is a greater demand for wood; it is needed for building materials and fuel. Cutting down areas of woodland also increases the amount of land available for agriculture. This leads to more trees being cut down, so fewer roots mean that soil is more vulnerable to erosion.

Irrigation – Depletes surface water and may involve unsustainable pumping of aquifers. As water levels decrease, water availability for plants decreases leading to less vegetation cover and soil erosion. Some irrigation techniques erode soil directly – surface irrigation washes top soil away. If too much water is used to irrigate the crops, excess can sink into the soil and raise groundwater levels. If the aquifer is saline, high concentrations of salt may be brought to the surface, increasing the salinity of the soil. This is known as Salinisation, and plants may be unable to survive.

Land
As fertile top soil is eroded, land becomes unproductive.

Ecosystems
Less plant life can be supported by the soils. This means that fewer animals can be sustained, and so biodiversity decreases.

Populations
If agricultural production decreases to the point where farmers cannot feed their families or earn a living, they may have to migrate from the area. The land which people move to will be put under increased pressure. If people are unable to move, a community’s inability to produce the food they require may led to famine.

Case study

Desertification in the Sahel
The Sahel is a 3900km long belt that runs East to West across Africa. It separates the hyper-arid Sahara from the wetter Savannah to the South. The Sahel runs through 10 countries, some of which are the poorest in the world, including Niger and Mali.