The Sahel is a semi-arid belt in Africa, stretching from the Atlantic Ocean to the Red Sea. It serves as a transitional zone between the Sahara Desert to its north and the more humid savannas to its south, encompassing parts of countries like Senegal, Mauritania, Mali, Burkina Faso, Niger, Chad, and Sudan. This region faces a significant environmental challenge: the expansion of desert-like conditions, known as desertification, which threatens the livelihoods of millions.
Understanding Sahelian Expansion
The Sahel has a hot, semi-arid climate with distinct wet and dry seasons, receiving 200-800 mm of annual rainfall, mostly from May to September. Its ecosystem features low-growing grasses, thorny shrubs, and scattered trees like acacia and baobab. Sahelian expansion refers to desertification, a process where productive land loses its biological capacity and resembles a desert. This degradation is marked by the loss of vegetation cover, increased soil erosion by wind and water, and reduced capacity for the land to support agriculture or grazing. This transformation is evident in the shrinking of major water bodies, such as Lake Chad, which contracted from 23,500 km² in 1963 to 2,000 km² by 1985. Satellite imagery and ground assessments show the Sahara Desert encroaching southward into the Sahelian steppes.
Climatic Influences
Changes in rainfall patterns are a primary climatic factor in the Sahel’s expansion, marked by decreased overall precipitation and increased variability. The Sahel’s rainfall is highly susceptible to influences from remote oceans and regional land-sea contrasts. Historically, the region experienced wet years in the early 20th century, followed by a decline in seasonal rainfall and severe droughts in 1972 and 1983-1984.
Rising temperatures, linked to global climate change, also contribute. The Sahel is projected to experience temperature increases significantly higher than the global average, with forecasts suggesting a rise between 2.0 and 4.3 °C by 2080 and spring seasons potentially becoming prolonged heatwaves. Higher temperatures increase evaporation, reduce soil moisture, and stress vegetation, making the land more vulnerable to degradation.
Large-scale atmospheric and oceanic circulations influence Sahel rainfall. The Atlantic Multidecadal Oscillation (AMO), a cyclical shifting of North Atlantic ocean temperatures, significantly impacts rainfall. A warm AMO phase is associated with increased rainfall, while a cool phase leads to reduced precipitation. The El Niño Southern Oscillation (ENSO) typically brings drier conditions to the Sahel during its rainy season, impacting rainfall variability.
Human Activities and Land Use
Human activities contribute to land degradation and desertification in the Sahel. Unsustainable agricultural practices are a major factor, with 80-90% of the population engaged in agriculture. Monoculture, insufficient fallow periods, and soil nutrient depletion degrade the land, reducing vegetation cover and increasing vulnerability to wind erosion.
Overgrazing by livestock also impacts the fragile ecosystem. The number of grazing animals often exceeds the region’s carrying capacity, leading to the removal of ground cover, trampling of vegetation, and soil compaction. This leaves bare land, particularly around water sources and settlements, increasing susceptibility to erosion.
Deforestation is driven by demand for fuelwood, construction materials, and agricultural expansion. For example, few trees remain within 90km of Khartoum in Sudan, and wood demand in Burkina Faso far outstrips natural regeneration. Removing trees eliminates roots that bind the soil, making it vulnerable to erosion and accelerating desertification. Population growth further pressures natural resources, as a rapidly expanding population requires more land for food and fuel. Sahelian countries have some of the fastest-growing populations globally, with projections indicating a doubling to around 200 million by 2050 in the Western Sahel.
Interactions and Reinforcing Cycles
The Sahel’s expansion results from complex interactions between climatic and human factors, creating self-reinforcing feedback loops. Land degradation, intensified by human activities like overgrazing and unsustainable farming, impacts the region’s climate. The loss of vegetation reduces moisture recycled into the atmosphere through evapotranspiration, leading to less local rainfall.
Degraded land, stripped of vegetation, also has a higher albedo, reflecting more sunlight. This increased reflectivity causes a cooling effect in the lower atmosphere, suppressing cloud formation and rainfall, and exacerbating drought. This feedback loop shows how human-induced degradation reduces rainfall, making the land less hospitable for vegetation and accelerating desertification.
Climate variability, such as prolonged droughts or erratic rainfall, makes human land use practices unsustainable. During dry periods, fragile soils become more susceptible to erosion, and vegetation struggles to recover. This pushes communities to intensify land use in remaining productive areas, further disrupting sustainable land management. The combined stress from a changing climate and intensive human activities amplifies negative impacts, accelerating the Sahel’s expansion.