According to the United Nations Environment Programme (ˇ§UNEPˇ¨) 40% of the total land on Earth is undergoing desertification and affects 32% of the human population. Desertification is mainly caused by climatic variations such as reduction in annual rainfall, as well as human activities including over-cultivation, over-grazing, deforestation, and poor irrigation management. These activities further exacerbate the desertification situation and, as a result, the land affected by desertification has been increasing at an annual rate of 10,400 km2 since the late 90s.
Desertification begins with the loss of vegetation and plant cover due to climatic or human events. This has several consequences:
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Loss of plant cover means that the rain falls directly onto the ground. This increased surface runoff washes away the fertile topsoil, nutrients and minerals.
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Because surface runoff is increased, the precipitation will not seep into the underground water table but rather run along the surface in streams or rivers. This will eventually lead to a reduction of underground water resources in the area, causing the land to become dry and arid.
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Plant root systems will hold layers of soil together preventing its erosion. The reduction in plant populations means that the soil is loose and will easily be eroded by wind or water.
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The fertility of the land is dependent upon biodegradation of dead biomass from plants. The effect of reduced vegetation means that there is less topsoil being regenerated by dead plants.
As a result, the land becomes infertile and without vegetation to trap moisture, the prevailing climate becomes ever dryer and more desert-like. This situation eventually degenerates into full-blown desertification. The reduction in soil productivity and the weakened condition of the landˇ¦s natural resilience will diminish crop yields and cause local farmers to lose their livelihoods. |