The degradation of land in arid or semiarid regions caused by climatic changes, human influence, or both. Climatic factors include periods of temporary but severe drought and long-term climatic changes toward dryness. Human factors include artificial climatic alteration, as through the removal of vegetation (which can lead to unnaturally high erosion), excessive cultivation, and the exhaustion of water supplies. Desertification drains an arid or semiarid land of its life-supporting capabilities. It is characterized by a declining groundwater table, salt accumulation in topsoil and water, a decrease in surface water, increasing erosion, and the disappearance of native vegetation.