About one third of the world’s surface is desert or semi-desert. Desserts are dry areas, with high temperature and little or no rainfall. The greatest deserts of the world are Sahara and Kalahari in Africa.
Now question arises, why are the deserts have not always been the same as we know now and why they are getting escalated day by day? For instance, prehistoric cave paintings of animals like giraffes and elephants in the middle of Sahara desert were found. Even evidences were found that Romans grew wheat in some areas in North Africa which are now desert. These indicate that these areas were transformed to desert from human inhabits.
Strong winds move sands further out to cover the neighbouring land areas. It is often seen particularly in regions of deserts. The action of wind on bare surface of the deserts reduces loose top soils to fine particles of sand. In sandy deserts, the surface is blown into raised strips. These are called sand-dunes. The constant movements of sands from one side of a dune to the other shifts the dune in larger areas – causing the expansion of the desert. Moreover, due to a very hot and dry atmosphere and also in absence of any vegetation, the process gets accelerated.
Other prime reasons for such phenomena are due to bad farmings. If a big field of light soil, for instance, is cultivated and left bare or too many trees are cut down, soil will blow away. Too many animals like sheeps or goats grazing on a semi-desert area may cause expansion of desert to its full form. Besides these, many wells and pumps down the underground water levels affect the soil to help the formation of new desert areas.
In modern arid-zone research techniques, several measures are undertaken to control these problems. Various methods such as preventive fencing, plantation of suitable grasses or plants are some of the techniques which help to stop the advance of deserts. In this way certain parts of deserts in the world have been transformed to agricultural lands for growing selected crops. This is however, still in experimental stage.