Desertification is land degradation occurring in arid, semi-arid, and dry sub-humid areas, resulting from climatic variations and human activities. This process is not the literal expansion of existing deserts, but the loss of biological productivity in vulnerable drylands, which cover over 40% of the Earth’s land surface. Identifying the most affected geographical areas is a focus of global environmental efforts, as this degradation directly threatens the livelihoods and food security of billions worldwide. Susceptibility varies significantly across continents due to environmental fragility and intense human pressure.
Defining Susceptibility and Global Dryland Categories
Susceptibility to desertification is fundamentally linked to a region’s climatic classification, extending beyond hyper-arid deserts. Organizations like the United Nations Convention to Combat Desertification (UNCCD) classify vulnerable areas as “drylands” using the Aridity Index (AI). This index is the ratio of annual precipitation to potential evapotranspiration (P/PET). Drylands are defined as areas where this ratio falls between 0.05 and 0.65, meaning water loss potential significantly exceeds actual rainfall. The dryland category includes dry sub-humid, semi-arid, and arid regions, all subject to land degradation. These conditions establish the baseline for inherent susceptibility, indicating low natural resilience to drought and resource use.
Primary Hotspots: The Sahel and Central Asian Steppes
The most acute instances of desertification are concentrated in the Sahel region of Africa and the expansive steppes of Central Asia. The Sahel, a semi-arid belt stretching from Senegal to Sudan, is a fragile transitional zone between the Sahara Desert and the wetter savannas to the south. This region has inherently marginal rainfall, often compounded by multi-year drought cycles, making the land vulnerable to degradation. High population density intensifies the issue, placing pressure on sparse vegetation and limited water resources.
The Central Asian steppes, encompassing countries such as Uzbekistan, Kazakhstan, and Turkmenistan, are another primary global hotspot. Degradation here is tied to historical, large-scale irrigation projects and unsustainable agricultural practices. For instance, the shrinking of the Aral Sea basin has left vast salt flats, which generate toxic dust storms that degrade surrounding agricultural land. Over-cultivation and poor water management have led to widespread soil salinization, rendering large tracts of once-productive land barren.
Secondary Zones of Concern: The Americas and Australia
Other significant portions of the globe face severe desertification, including vulnerable zones across the Americas and Australia. In North America, the US Southwest (Arizona and New Mexico) and northern Mexico are particularly susceptible. Here, cyclical drought, exacerbated by rising temperatures and water scarcity, puts strain on riparian areas and rangelands. This vulnerability is tied to the over-extraction of surface and groundwater resources for agriculture and urban use.
South America contains highly susceptible areas, notably the Patagonian Steppe in Argentina and the Caatinga biome in Brazil’s Northeast. The Patagonian region suffers from wind erosion intensified by overgrazing, which strips the sparse vegetation cover and exposes the fragile soil to arid winds. The Caatinga, a dry sub-humid ecosystem, is frequently subjected to prolonged droughts and deforestation for wood fuel, leading to extensive land degradation. Australia, a continent with a vast dry interior, experiences degradation primarily through soil salinity and the impact of extreme weather events in its rangelands.
Human and Geological Factors Accelerating Degradation
The transformation of susceptible drylands into degraded landscapes is directly accelerated by specific human activities and inherent geological conditions. Unsustainable land use practices are major anthropogenic drivers. These include overgrazing, which removes protective vegetation cover, leaving the soil exposed to wind and water erosion. Deforestation, often for wood fuel collection, eliminates the root systems that bind the soil and disrupts local hydrological cycles. Poor irrigation techniques in arid environments often lead to waterlogging and subsequent salinization, where the evaporation of water leaves behind a toxic concentration of salt in the topsoil.
Geological and soil factors provide the underlying fragility that makes these regions prone to rapid degradation. Many dryland soils are naturally fragile, possess low organic matter content, and are inherently thin, making them highly susceptible to wind erosion. Once the protective layer of vegetation is lost, these fine soils are easily carried away by wind, leading to dust storms and leaving behind infertile, compacted subsoil. The combination of these inherent soil limitations and intense human exploitation creates a destructive feedback loop that accelerates the desertification process.