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Its signs are subtle and slow: the earth dries; water levels fall; the rains do not come; and the land is gripped by drought.
干旱的迹象很微小很缓慢：地面干燥；水位下降；雨季不到；土地龟裂。
At its most basic, a drought occurs when more water is used than is replenished.
最根本的原因是，当水量应用超过水量补给时，就会发生干旱。
It is a balance between supply and demand, with both natural and human factors in play.
供给和需求之间有一个平衡点，这要考虑自然和认为因素。
The weather is constantly in flux. A low pressure system allows moist air to rise, cool and form rain clouds.
天气是变幻无常的。低气压系统使潮湿的空气上升，冷凝，形成降雨云。
A high pressure system traps the air beneath it, and banishes the clouds.
高气压系统挤压下面的空气，将云消除。
Droughts form when changing wind patterns cause high pressure systems to last for months, or even years.
当变化的风向造成高气压系统持续数月甚至几年的时间时就会发生干旱。
Aggravating the problem is society's demand for water. Farms are heavily dependent on water to irrigate crops and provide pasture for livestock.
社会对水的需求量使这个问题更加恶化。农田以来水来灌溉作物，为牲畜提供牧场。
Urban areas also place huge demands on available water supplies. If the demand can't be reduced, then the drought begins to take its toll.
城市地区也对可用水供应有大量需求。如果需求两不能降低，干旱就会造成损失。
Crops eventually wither and die. Soil erodes away into clouds of dust. Forest fires spread rapidly.
庄稼最终枯萎，死亡。土壤变成灰尘流失。森林大火迅速蔓延。
The damage to the environment has large-scale consequences for us human population.
对环境造成的损害也对人类造成大规模的影响。
Short-term droughts cause stress on both the environment and people.
短期干旱对环境和人类都造成压力。
Long-term droughts can lead to war, famine, disease or mass migrations.
长期的干旱可能会导致战争，饥荒，疾病和大规模的人口迁移。
In the 1930s, a severe drought in the Great Plains caused massive crop failures. In some places, the drought lasted 8 years.
上世纪30年代，大平原地区发生了严重的干旱，导致大面积作物歉收。在有些地区，干旱持续了长达八年时间。
So much soil blew away became known as the Dust Bowl.
土壤被风吹走，形成人所共知的沙尘暴。
Over 50 million acres of land were affected, forcing many farmers to abandon their own property.
5000多万英亩的土地受到影响，许多农民被迫遗弃他们的财产。
But by historical standards, the Dust Bowl was mild and short-lived. Some droughts have lasted for decades.
但是根据历史标准，沙尘暴不比较温和，持续时间比较短。有的干旱延续达几十年之久，
The famines they create have killed over 40 million people in the 20th century alone.
造成的饥荒仅仅在20世纪就使4000多万人丧命。
Like other forms of weather, droughts are one of the earth's natural processes. There is very little we can do to stop them.
像其他形式的天气一样，干旱是地球自然过程的一种。我们无法阻止他们。
The best we can do is prepare for when droughts do come before everything blows away.
我们能做到最好的就是当为干旱做好准备，以防一切都被吹走。
