Desertification: Causes, Effects and Control

1A desert that is not advancing

In the 1970s many reports pictured the Sahara as a wall of sand marching south across the Sahel at several kilometres a year. Satellite records since the 1980s tell a more complicated story: much of the Sahel became greener as rainfall partly recovered, while particular villages, pastures and fields went on losing their soil. Desertification is not mainly a moving desert. It is land that people depend on losing its ability to produce, patch by patch, wherever the land is dry.

Figure 1: the aridity index and the dry zones named by the UNCCD. True deserts (hyper-arid) are already deserts; desertification happens in the three zones between 0.05 and 0.65.

Drylands cover about 41% of the Earth's land and are home to over 2 billion people (UNCCD). The IPCC's special report Climate Change and Land (2019) estimates that about 500 million people lived in areas that experienced desertification between the 1980s and the 2000s, most of them in South and East Asia, around the Sahara and in the Middle East.

2Causes

Figure 2: the vicious circle of desertification. Each turn of the circle leaves less productive land to meet the same or greater demand; drought speeds it up.

3Effects

• Farming and food: lower crop yields and less pasture, leading to food insecurity and, in severe droughts, famine, as in the Sahel in 1968–1974 and again in the early 1980s.
• Soil and water: topsoil blown or washed away; crusted soils that shed rain instead of absorbing it; wells and seasonal lakes drying; salt crusts on irrigated land.
• People: migration from rural areas to towns or across borders; competition between farmers and herders for land and water, which can turn violent.
• Environment: loss of plant and animal species; dust storms that damage health, ground aircraft and carry soil across oceans; less carbon stored in soils and vegetation.
• Climate feedback: bare, bright soil reflects more sunlight than vegetation (a higher albedo), which may weaken the rising air that brings rain, a hypothesis first proposed by Jule Charney in 1975.

4Control: what works?

The Great Green Wall, launched by the African Union in 2007, began as a plan for a belt of trees across Africa from Senegal to Djibouti. It has since become a mosaic of land-restoration projects with a target, set by the UNCCD, of restoring 100 million hectares of degraded land by 2030. Progress has been slow and uneven: trees planted without the involvement of local people often die, while restoration led by farmers themselves has done better.

5Rwanda and desertification

Rwanda has no desert, and most of the country is humid. Its main form of land degradation is soil erosion on steep, wet hillsides, which, by the UNCCD definition, is land degradation rather than desertification. The drier lowlands of the Eastern Province, such as Bugesera, Kayonza and Nyagatare, receive less rain and are the parts of the country most exposed to drought. Rwanda is a party to the UNCCD, and its measures there overlap with its climate adaptation: water harvesting, irrigation, drought-tolerant crops, agroforestry and the protection of remaining forests.

6Discuss

Some geographers argue that the word "desertification" encourages governments to blame the climate, or herders, for problems that also come from land policy and poverty. Using the Sahel greening map and the Great Green Wall, discuss whether the problem is better described as "land degradation in drylands".