For an area to be considered desert, it needs to combine at least two elements: sandy soil and a hot, dry climate, with very low levels of rainfall over a long period. The deserts that exist on Earth today have for thousands of years experienced an average rainfall of less than 250 millimeters per year, an index six times lower than that of the city of São Paulo, for example. This means that it takes a long time for a desert to appear. “Therefore, it is not true that desert areas are advancing across the Earth’s surface during the last few decades. The presence of sand, by itself, does not characterize a desert”, says geographer Roberto Verdum, from the Federal University of Rio Grande do Sul (UFRGS). The origin of so much confusion is the wrong understanding of the concept of desertification. In its correct sense, the word indicates the expansion of sandy lands across the planet – generally due to soil depletion – and not deserts. More: contrary to what is thought, it is not an irreversible phenomenon.
“Recent studies show that areas that suffered from desertification can recover their vegetation cover when the most acute drought period ends”, says Roberto. Of course, this does not diminish the seriousness of the problem. Worldwide, it is estimated that desertification affects 1 billion people in about 110 countries, even threatening a third of the land on the globe. The continent most affected is Africa, where 73% of arable land has already suffered some degree of degradation. In Brazil, desertification is advancing over an area of 1 million square kilometers in the northeastern semi-arid region and in the north of Minas Gerais. To combat the problem, the United Nations (UN) launched the Convention to Combat Desertification, an international agreement in force since 1994 and signed by more than 180 countries – Brazil is one of them. But until now, investments have been timid and have not been able to prevent the sands from advancing at a speed of 60,000 square kilometers per year.
1. In areas with sandy terrain, native forest is essential to protect the soil from degradation. Tree roots support the earth and retain water, preventing erosion. The situation begins to change when the area is occupied in a predatory manner. Deforestation of native vegetation or on the banks of rivers, fires, intensive farming, indiscriminate use of pesticides and inadequate irrigation practices can initiate the process of desertification
2. With agricultural occupation, part of the native forest is cut down to make way for plantations. Without the protection of the roots, the soil loses organic matter and begins to have layers removed. With each new crop, the plowing of the land and the action of rain carry nutrients from the soil and reduce its original thickness. Bare land suffers from erosion and riverbeds shrink from landslides
3. The bad use of the soil puts an end to productivity in the lowlands and forces the farmer to deforest an area on the slope to proceed with planting. In this region, the effects of erosion are even faster. Abandoned lands only serve as pasture for cattle. In some years, the productivity of the slopes also decreases and the flat strip has already turned to sand.
4. In a few decades, the fertile and green region gives way to sandy and unproductive land. With the action of wind and water, the entire strip of soil has already disappeared and only sand and rock remain. But that doesn’t mean that the area has become a desert, because desolation can be cured: all you have to do is clear the area for more resistant grasses and grasses to reappear. Full soil recovery, however, can take centuries.
Africa is by far the continent hardest hit by desertification. On the southern edge of the Sahara desert, a region the size of the state of Minas Gerais has turned to sand over the past 50 years. Today, the threat of desertification affects almost two-thirds of the continent. In addition to the constant droughts, the soils have suffered from the replacement of livelihood crops by export crops since the 1940s. The problem has serious social consequences: in the next two decades, around 60 million people will have to leave the lands affected by desertification, migrating to North Africa or Europe.