The extension of deserts at the expense of cultivable lands is called desertification.
Desertification is defined as a process of land degradation in arid, semi-arid and sub-humid areas due to various factors including climatic variations and human activities. Or, to put it in another way, desertification results in persistent degradation of dryland and fragile ecosystems due to man-made activities and variations in climate. Desertification, in short, is when land that was originally of another type of biome turns into a desert biome because of changes of all sorts. A huge issue that many countries have is the fact that there are large pockets of land that are going through a process that is known as desertification.
Overgrazing is the major cause of desertification worldwide. Other factors that cause desertification include urbanization, climate change, overdrafting of groundwater, deforestation, natural disasters and tillage practices in agriculture that place soils more vulnerable to wind. Desertification affects topsoil, groundwater reserves, surface runoff, human, animal and plant populations. Water scarcity in drylands limits the production of wood, crops, forage and other services that ecosystems provide to our community.