文档介绍：土地沙漠化
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荒漠
一种残缺的美…
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荒漠
—美丽背后的忧患
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狭义的荒漠化（即：沙漠化）
在脆弱的生态系水减少等等。
According to the feedback, the possibility of convective precipitation is reduced as the soil moisture decreases and evaporation decreases after the drought begins. Overgrazing in semi-arid regions increases ground reflectivity, changes ground energy balance, and leads to subsidence movement, resulting in prolonged drought. The disappearance of biological source material in rain clouds causes the reduction of precipitation, etc.
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天文说：认为由于地球轨道参数变化，使中高纬度夏季辐射量减少，导致冰期的发生和沙漠区的扩大。
变冷说：认为气候变冷导致降水能源减少，蒸发量减少，干旱使沙漠扩大。
Astronomical theory: it is believed that due to changes in earth orbit parameters, summer radiation in the middle and high latitudes is reduced, resulting in the occurrence of ice age and expansion of desert areas.
Cooling: climate cooling leads to less precipitation, less energy, less evaporation and more desert expansion.
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产生沙漠化的自然因素主要是干旱、地表为松散砂质沉积物和大风的吹扬等；人为因素主要是过度放牧、过度垦殖、过度樵柴和不合理地利用水资源等。
The natural factors of desertification are drought, loose sandy sediment on the surface and wind blowing. Human factors mainly include overgrazing, overreclamation, excessive firewood and unreasonable utilization of water resources.
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举例：文明发祥地
中东的美索不达米亚（今伊拉克）地区是世上最早发展农业的地域之一，从而发展成世上最早的文明发祥地之一。美索不达米亚的土壤本来甚为肥沃，不过由于过度的农业活动、人们不理会土地长期枯渴，更开发河段上流、采伐森林，上流土地从而不能吸收降雨，雨水一气流入河中造成水土流失以及洪水。
Mesopotamia (now Iraq) in the Middle East was one of the first regions in the world to develop agriculture, and thus became one of the earliest cradles of civilization in the world. The soil of Mesopotamia was originally very fertile. However, due to excessive agricultural activities, people ignored the long-term thirst of the land, and developed the upper reaches of the river and harvested forests, which could not absorb the rainfall. The rain water flowing into the river caused soil erosion and flood.
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