国家地理-2008-09-11 旱灾的成因与影响

Its signs are subtle and slow: the earth dries; water levels fall; the rains do not come; and the land is gripped by drought. At its most basic, a drought occurs when more water is used than is replenished¹. It is a balance between supply and demand, with both natural and human factors in play.

 

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.

 

1 replenished   

补充( replenish的过去式和过去分词 )； 重新装满

参考例句：

• She replenished her wardrobe. 她添置了衣服。
• She has replenished a leather [fur] coat recently. 她最近添置了一件皮袄。

2 flux   

n.流动；不断的改变

参考例句：

• The market is in a constant state of flux.市场行情在不断变化。
• In most reactors,there is a significant flux of fast neutrons.在大部分反应堆中都有一定强度的快中子流。

3 banishes   

v.放逐，驱逐( banish的第三人称单数 )

参考例句：

• Work banishes those three great evils: boredom, vice, and poverty.(Voltaire, French philosopher) 工作撵跑三个魔鬼：无聊、堕落和贫穷。（法国哲学家伏尔基泰） 来自互联网
• The Consumer: It Banishes Uterine Fibroids, but for How Long? 消费者：它驱逐子宫的纤维瘤，但是为多久？ 来自互联网

4 aggravating   

adj.恼人的，讨厌的

参考例句：

• How aggravating to be interrupted! 被打扰，多令人生气呀！
• Diesel exhaust is particularly aggravating to many susceptible individuals. 许多体质敏感的人尤其反感柴油废气。

5 irrigate   

vt.灌溉，修水利，冲洗伤口，使潮湿

参考例句：

• The farmer dug several trenches to irrigate the rice fields.这个农民挖了好几条沟以灌溉稻田。
• They have built canals to irrigate the desert.他们建造成水渠以灌溉沙漠。

6 livestock   

n.家畜，牲畜

参考例句：

• Both men and livestock are flourishing.人畜两旺。
• The heavy rains and flooding killed scores of livestock.暴雨和大水淹死了许多牲口。

7 toll   

n.过路(桥)费；损失，伤亡人数；v.敲(钟)

参考例句：

• The hailstone took a heavy toll of the crops in our village last night.昨晚那场冰雹损坏了我们村的庄稼。
• The war took a heavy toll of human life.这次战争夺去了许多人的生命。

8 wither   

vt.使凋谢，使衰退，(用眼神气势等)使畏缩；vi.枯萎，衰退，消亡

参考例句：

• She grows as a flower does-she will wither without sun.她象鲜花一样成长--没有太阳就会凋谢。
• In autumn the leaves wither and fall off the trees.秋天，树叶枯萎并从树上落下来。

9 erodes   

侵蚀，腐蚀( erode的第三人称单数 )； 逐渐毁坏，削弱，损害

参考例句：

• The sea erodes the rock. 海水侵蚀岩石。
• The sea erodes the land. 海洋侵蚀陆地。

10 migrations   

n.迁移，移居( migration的名词复数 )

参考例句：

• It foundered during the turmoils accompanying the Great Migrations. 它在随着民族大迁徙而出现的混乱中崩溃。 来自辞典例句
• Birds also have built-in timepieces which send them off on fall and spring migrations. 鸟类也有天生的时间感应器指导它们秋春迁移。 来自互联网

11 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。