Desertification
Desertification is when land that used to support farming, animals and people gradually turns into desert. Every year an area roughly the size of Greece changes from productive land into bare soil. Around 250 million people are directly affected and another billion are at risk. The good news is that the process can be stopped and even reversed with the right work. The Great Green Wall of Africa is one of the most ambitious responses on Earth.
- Land lost per yearapprox. 12 million hectaresRoughly the size of Greece
- People affectedapprox. 250 million directlyAnother billion are at risk
- Worst affectedThe SahelSouthern edge of the Sahara
- Main causesClimate + peopleDrought, overgrazing, deforestation
- Biggest projectGreat Green Wall8,000 km belt across Africa
- Can it be reversed?YesNiger has restored 5 million hectares
Land lost to desertification per year
Africa loses the most land to desertification each year, mostly along the southern edge of the Sahara. Climate change is making the rate worse.
What is desertification?
Desertification is the process by which productive land (farms, grasslands, forests) gradually loses its ability to support plants and becomes more desert-like. The land may not look exactly like a sand dune at the end, but it loses its topsoil, its plants and its ability to grow crops or feed grazing animals. Desertification mostly happens in drylands, the regions of the world that are already dry but not yet quite desert: the savannas, the steppes, the Mediterranean shrublands.
What causes it?
Desertification is usually caused by a combination of natural and human factors:
- Climate change is making many already-dry regions even drier. Rainfall is becoming less reliable, droughts longer and more severe.
- Overgrazing. When too many cattle, goats or sheep eat the grass in one area, the roots cannot hold the soil, and the plants cannot recover. The bare soil then blows or washes away.
- Deforestation. Cutting down trees for firewood, charcoal or land clearing removes the roots that hold soil in place and the canopy that shades it from drying out.
- Unsustainable farming. Planting the same crop year after year without resting the soil exhausts its nutrients. Ploughing fragile dry-zone soils exposes them to wind erosion.
- Population pressure. Growing populations need more food, more firewood, more land. The pressure can push farming and grazing into areas that cannot really support them.
The Sahel: the worst affected region
The most seriously affected region on Earth is the Sahel, the band of dry grassland that runs across Africa just south of the Sahara Desert. The Sahel was hit by repeated catastrophic droughts in the 1970s and 1980s, killing hundreds of thousands of people and displacing millions. Climate change is making the droughts more frequent and severe. The Sahara has advanced significantly southward into former Sahelian grassland over the past century.
The Sahel also illustrates how desertification feeds conflict and migration. Failed harvests push rural people into cities or across borders. Competition for shrinking pastures and water sources fuels conflicts. Many of the migrants trying to cross the Mediterranean to Europe come from the Sahel region.
Can desertification be reversed?
Yes, with the right effort. Several techniques have worked at large scale:
- Tree-planting. Trees hold soil in place, shade the ground, and bring up moisture from deep underground. Africa's "Great Green Wall" plans to plant trees across an 8,000 km strip from Senegal to Djibouti.
- Farmer-managed natural regeneration. Letting native trees and shrubs grow back from their roots and seeds in farm fields. Niger has restored over 5 million hectares this way at little cost.
- Better grazing management. Moving livestock between pastures gives the grass time to recover. Rotation systems modelled on traditional methods can dramatically improve soil and forage.
- Water harvesting. Building small stone walls (called "half-moons") on hillsides catches rare rains and slows runoff, letting water soak in.
- Better crop choices. Drought-resistant crops, mixed farming, agroforestry (growing trees and crops together).
Deeper dive: the science of land degradation, the Great Green Wall, and farmer-managed natural regeneration
The science of desertification has evolved significantly over the past few decades. Early thinking saw desertification as a one-way process driven mostly by overgrazing: a deterministic march of the desert against human activity. More recent research recognises that drylands are inherently variable, with vegetation cover swinging up and down with rainfall over years and decades. The question is not whether vegetation cover sometimes drops to low levels, but whether it can recover when rains return. Healthy drylands recover; degraded drylands do not. The difference often lies in the state of the soil, the seed bank, and the human management systems that govern grazing and harvesting. Modern dryland scientists therefore focus on resilience and recovery, not just on stopping degradation.
The African Great Green Wall initiative, launched by the African Union in 2007, is the largest land restoration project on Earth. The original concept was to plant a continuous belt of trees 15 km wide and 8,000 km long across the southern edge of the Sahara, from Senegal in the west to Djibouti in the east. After 15 years of patchy implementation, the Great Green Wall has been redesigned: instead of a single continuous wall (which would be ecologically inappropriate in many areas), it is now conceived as a mosaic of integrated land restoration efforts using a wide variety of techniques. Tree planting where appropriate, farmer-managed natural regeneration, water harvesting, soil restoration, and protected area expansion are all components. Funding has come from the World Bank, the EU, the UN and dozens of national governments, but implementation has often been slow. Pilot projects have shown remarkable local successes; scaling them up across an entire continent remains a major challenge.
The most cost-effective desertification reversal technique discovered in recent decades is farmer-managed natural regeneration (FMNR), pioneered in Niger in the 1980s. FMNR is breathtakingly simple: instead of clearing all the trees and shrubs from fields (the traditional African farming practice), farmers identify promising young trees that sprout from old root systems and protect them by selectively cutting back competing shoots. Within a few years, the field has a scattered canopy of mature trees alongside the growing crops. The trees provide shade, fix nitrogen, hold soil, drop leaves that fertilise the soil, and produce wood, fruit or fodder. Crop yields underneath the trees increase significantly. The technique requires almost no equipment, no external inputs, and no money. It can be scaled up by farmers teaching other farmers. Niger's 5 million hectares of FMNR-restored land is the largest documented land restoration in the world. The technique is now spreading to other countries across the Sahel and beyond.
The most affected desert region is the Sahara and its southern edge. For the wider context of dryland ecosystems, see desert ecosystems.