Much of the land surrounding the Sahara desert has been cleared for crop farming so many of the scrub trees, vital in preventing complete desertification, have been destroyed. The wood has been used for firewood and the land has been overgrazed by the domestic animals. This has altered the microclimate which has allowed the desert to encroach southwards into areas of former Savanna. The removal of natural vegetation cover has also led to an increase in soil erosion by both wind and the infrequent falls of rain. The result is that over many areas of Ethiopia and Sudan people have migrated from the worst hit areas, i.e. where sand dunes have encroached on villages and farmland at the desert's margins.
People are then overcrowded in small areas where the land is fertile.
This land is, in turn, over used and the people move elsewhere. This unsustainable management of the land has been the 'trigger' for short-term human misery and disaster. Another problem with increasing deserts is the amount of soil erosion that can take place. For instance if there are no obstacles to stop the wind, it can pick up speeds and blow much of the useful topsoil away. This further prevents any vegetation from growing.