Why? The difficulties start with the sheer number of people using the stuff. When, 60 years ago, the world's population was about 2.5 billion, worries about water supply affected relatively few people. Both drought and hunger existed, as they have throughout history, but most people could be fed without irrigated farming. Then the green revolution,in an inspired combination of new crop breeds, fertilizers and water, made possible a huge rise in the population. The number of people on Earth rose to 6 billion in 2000, nearly 7 billion today, and is heading for 9 billion in 2050. The area under irrigation has doubled and the amount of water drawn for farming has tripled. The proportion ofpeople living in countries chronically short of water is set to rise from 8% at the turn of the 21st century to 45% by 2050.
为什么会是这样呢？首要的困难就是用水的人实在太多。60年前，世界人口约为25亿，供水问题只影响到较少的人。那时也有干旱和饥荒，就像它们在整个人类历史进程中都存在—样，但是多数人还可以不靠灌溉农业为生。后来绿色革命兴起了，它将新品种的培育、肥料和水的使用有机地结合起来，使得人口剧增。地球上的人口在2000年猛增到60亿，现在已接近70亿，到2050年将逼近90亿。用水灌溉的土地面积已经翻番，农业用水量增加了两倍。到2050年，居住在长期缺水的国家的人口比例将由21世纪初的8%上升到45%。
Farmers' increasing demand for water is caused not only by the growing number of mouthsto be fed but also by people's desire for better-tasting, more interesting food. Unfortunately, it takes nearly twice as much water to grow a kilo of peanuts as a kilo of soybeans, nearly four times as much water to produce a kilo of beef as a kilo of chicken. With 2 billion people around the world about to enter the middle class, the agricultural demands on water would increase even if the population stood still.
农民对水不断增长的需求不仅仅是因为不断增加的人口需要养活，还因为人们对味道更好、更刺激他们味蕾的食品的追求。不幸的是，种植一公斤花生比种植一公斤大豆多需要近一倍的水；要生产一公斤牛肉比生产一公斤鸡肉要多用近三倍的水。随着世界上有20亿人口就要进入中产阶层，即便人口不再增长，农业用水的需求也会增加。
来源:可可英语 http://www.kekenet.com/daxue/201810/566579.shtml
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