desertification

Land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities. Patches of degraded land may develop hundreds of kilometres from the nearest desert. But these patches can expand and join together, creating desert-like conditions. Desertification contributes to other environmental crises, such as the loss of biodiversity and global warming. Drought often triggers desertification, but human activities are usually the most significant causes. Over-cultivation exhausts the soil. Overgrazing removes vegetation that prevents soil erosion. Trees that bind the soil together are cut for lumber or firewood for heating and cooking. Poorly drained irrigation turns cropland salty, desertifying 500,000 hectares annually, about the same amount of soil that is newly irrigated each year. (Source: ECOSOC)