Desertification often occurs because of poor land practices, including deforestation, overuse of farmland, overgrazing and poor irrigation techniques. Poor communities frequently place excessive demands on arid ecosystems, cutting down trees for firewood and over-farming marginal agricultural land. Throughout the world, herding societies that had previously moved seasonally to different grazing lands instead remain in one place throughout the year. Without a seasonal break for restoration, the land often becomes overgrazed and compacted, leaving it prone to erosion and resistant to absorbing rain. Poor irrigation techniques lead to a buildup of salt in the soil, leaving the land less productive. Global climate change also threatens to worsen desertification trends.
Soils in arid and semi-arid regions tend to be fragile, with topsoil relatively thin compared with regions with more rainfall. Loss of topsoil is both a cause and a consequence of desertification. While over-farming removes organic matter from the soil, removing tree cover and overgrazing reduce the amount of organic matter that gets returned to the soil. As soil becomes depleted, it becomes more prone to erosion. Desertification also leads to increased flooding during heavy rains, as compacted land fails to absorb water, further exacerbating erosion problems. Erosion in turn threatens remaining plant life, leading to a feedback loop that accelerates the desertification process.
Desertification tends to occur in areas with high levels of poverty. As land becomes less productive, human societies experience higher levels of poverty, food insecurity, water scarcity and disease. As agricultural yields drop or water becomes more scarce, poor communities often react by increasing the over-exploitation of remaining resources. As environmental degradation progresses and human communities become more desperate, crises can develop, including famine, wars and mass migrations.
While desertification is a worldwide problem, its effects are felt most acutely in Africa. Two-thirds of Africa is either arid, semi-arid or desert. African countries have high levels of poverty and often experience severe droughts. Desertification problems are most severe in sub-Saharan Africa, and in the southern portion of the continent. Besides Africa, desertification is causing considerable human hardship in the Indian subcontinent and central Asia.