Desertification, as the name implies, relates to the growing amount of the world's land that is turning into desert. It is happening because of a combination of human abuse of the land and adverse climatic conditions. It is a major problem facing the world particularly at a time when population is increasing at a rapid rate. As reported by the United Nations Convention to Combat Desertification (UNCCD) there are 250 million people directly affected by desertification and a billion people affected indirectly. These people include many of world's poorest and most marginalised who do not have the necessary skills or economy to manage these difficult soils.
There are significant areas of natural 'climatic' deserts around the world, many of which have been there for thousands of years, including the Sahara in North Africa, the Kalahari in southern Africa, the Atacama in South America, large parts of Australia and the Sonoran desert in southern United States and Mexico. These cover millions of hectares and apart from some oasis cultivation are largely unproductive. The strongest factor in their development has been the dry climate. Desertification is now spreading far beyond the climatic deserts into areas of vulnerable soils under a prevailing dry climate. It is a process that is now occurring not only in hyperarid areas, the true climatic desert regions, but also in arid, semi-arid and sub-humid zones, which have a ratio of rainfall: evapotranspiration of <0.05 to 0.70, where evapotranspiration exceeds incoming precipitation.
The areas affected by desertification have low rainfall, long dry periods or seasons, sparse vegetation cover, very thin loose soils, and surface deposits that are highly mobile. Under these circumstances the soil cover is prone to desiccation and easy removal by winds. There is now much evidence that human activity is triggering increasing desertification. In these marginal areas, agricultural production is much more difficult to achieve and it is difficult to avoid damage to the soils. The human impacts are a function of population density, cultural traditions, land tenure and land management and other socio-economic and political factors. Although climate and soil type are important in determining the severity and rate of desertification it is often ignorance in failing to match the use and management of the land with the prevailing climate that leads to the removal of the soil and irreparable damage.