英语听力：自然百科 旱灾的成因与影响

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The weather is constantly in flux². A low pressure system allows moist air to rise, cool and form rain clouds. A high pressure system traps the air beneath it, and banishes³ the clouds. Droughts form when changing wind patterns cause high pressure systems to last for months, or even years.

 

Aggravating⁴ the problem is society's demand for water. Farms are heavily dependent on water to irrigate⁵ crops and provide pasture for livestock⁶. Urban areas also place huge demands on available water supplies. If the demand can't be reduced, then the drought begins to take its toll⁷. Crops eventually wither⁸ and die. Soil erodes⁹ away into clouds of dust. Forest fires spread rapidly.

 

The damage to the environment has large-scale consequences for us human population. Short-term droughts cause stress on both the environment and people. Long-term droughts can lead to war, famine, disease or mass migrations¹⁰.

 

In the 1930s, a severe drought in the Great Plains caused massive crop failures. In some places, the drought lasted 8 years. So much soil blew away  became known as the Dust Bowl. Over 50 million acres of land were affected¹¹, forcing many farmers to abandon their own property.

 

But by historical standards, the Dust Bowl was mild and short-lived. Some droughts have lasted for decades. The famines they create have killed over 40 million people in the 20th century alone.

 

Like other forms of weather, droughts are one of the earth's natural processes. There is very little we can do to stop them. The best we can do is prepare for when droughts do come before everything blows away.

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