Desertification is a complex form of land degradation that occurs specifically in the world’s drylands, which include arid, semi-arid, and dry sub-humid regions. It is defined as the reduction or loss of biological and economic productivity of the land, resulting from a combination of climatic variations and human activities.
Drylands cover approximately 40% of the Earth’s terrestrial surface and are home to over two billion people globally, making the issue of desertification a serious environmental and humanitarian concern. The degradation of these areas threatens food security, reduces biodiversity, and contributes to the loss of fertile topsoil, with an estimated 24 billion tonnes of fertile soil lost globally each year.
Climatic Variability and Prolonged Drought
The baseline conditions for desertification are established by natural climate patterns, particularly the frequency and duration of drought. Prolonged periods of below-average rainfall reduce soil moisture significantly, which limits the growth and survival of vegetation.
Changing global weather patterns exacerbate these arid conditions by increasing heat stress and the unpredictability of precipitation. Higher temperatures cause increased evaporation from the soil surface, further drying the land and placing additional strain on water resources. This creates a positive feedback loop: when vegetation cover is lost, the exposed, dry soil reflects more sunlight and contributes to local atmospheric changes that can suppress rainfall, locking the region into a cycle of increasing aridity.
When rainfall does occur, it is often concentrated and intense, failing to adequately replenish the subsoil. Degraded and hardened soil surfaces cannot absorb water efficiently, leading to rapid surface runoff and erosion rather than deep infiltration. This means that the limited water available is lost quickly, washing away what little topsoil remains and preventing the land from retaining moisture needed to sustain plant life.
Unsustainable Land Use and Vegetation Removal
The physical removal of protective plant cover is a direct and immediate human cause that dramatically accelerates desertification. This process includes widespread deforestation for timber, clearing land for agricultural expansion, and the collection of shrubs and grasses for fuel or housing materials.
Root systems play a fundamental role by binding soil particles together, which resists displacement by wind and water. The removal of this biological structure exposes the topsoil, which is then easily carried away during windstorms or intense rain events. Furthermore, a biological crust, composed of cyanobacteria, lichens, and mosses, which helps stabilize the surface in drylands, is easily destroyed by traffic or clearing.
The loss of vegetation cover also disrupts the local water cycle, particularly in forested areas. Large-scale clearing reduces evapotranspiration. Consequently, the removal of forest cover can lead to a localized drying of the climate, making the land more susceptible to desertification.
Degradation Through Intensive Agricultural Practices
Beyond the initial clearing of land, the long-term management of dryland ecosystems through intensive agricultural practices actively degrades soil quality and structure. Overgrazing by livestock is a significant factor. Livestock consume vegetation faster than it can regenerate. This continuous pressure strips the land of its protective covering, which directly exposes the soil to erosion.
Livestock hooves compact the soil beneath them, especially when grazing is concentrated in specific areas. Soil compaction reduces the pore spaces within the soil, significantly decreasing its ability to absorb water and air. This prevents proper water infiltration, increases surface runoff, and limits the aeration necessary for healthy root growth and microbial activity.
Modern intensive farming methods, such as monocropping and heavy tillage, further contribute to degradation. Monocropping, the practice of growing a single crop repeatedly, rapidly depletes specific nutrients from the soil, leading to nutrient exhaustion. Tillage, especially with heavy machinery, destroys the natural soil structure and breaks down the organic matter that gives soil its resilience. Without sufficient organic matter and structure, the soil becomes loose and highly vulnerable to wind and water erosion, transforming productive fields into easily dispersed dust.
Soil Salinization and Water Mismanagement
Soil salinization represents a chemical form of land degradation specific to irrigated areas in dry climates, where the accumulation of soluble salts poisons the land. This process is primarily a consequence of poor irrigation management combined with high rates of evaporation. When farmers irrigate crops in arid or semi-arid regions, the majority of the water applied to the fields evaporates from the soil surface before it is fully absorbed by the plants.
The water used for irrigation contains dissolved mineral salts. As the water evaporates, it leaves these salts behind on the soil surface and in the root zone. Over time, this concentration of minerals reaches levels toxic to most conventional crops, inhibiting their ability to absorb water and eventually rendering the land unproductive.
Water mismanagement often exacerbates this problem, particularly when drainage is inadequate or water sources are overexploited. If subsurface drainage is insufficient, the water table can rise, bringing naturally occurring salts up to the root zone where they accumulate. The excessive pumping of groundwater can also lead to the use of deeper, more saline aquifers or, in coastal areas, cause saltwater intrusion, introducing more salt into the irrigation supply and accelerating the salinization cycle.