[2008.09.20] 农业用水：即将枯竭

Water for farming
农业用水

Running dry
即将枯竭

Sep 18th 2008
From The Economist print edition

The world has a water shortage, not a food shortage
现在，是水资源短缺，不是粮食短缺

MOST people may drink only two litres of water a day, but they consume about 3,000 if the water that goes into their food is taken into account. The rich gulp down far more, since they tend to eat more meat, which takes far more water to produce than grains. So as the world’s population grows and incomes rise, farmers will-if they use today’s methods-need a great deal more water to keep everyone fed: 2,000 more cubic kilometres a year by 2030, according to the International Water Management Institute (IWMI), a research centre, or over a quarter more than they use today. Yet in many farming regions, water is scarce and likely to get scarcer as global warming worsens. The world is facing not so much a food crisis as a water crisis, argues Colin Chartres, IWMI’s director-general.

大部分人一天的饮水量仅为2升，但若是将食物产出时所需水量一并算进，每天的耗水量就达到了3000升。富人往往吃更多的肉制品，而生产肉制品耗水比谷物制品多得多，因而富人消耗了大量的水资源。这样看来，随着人口和收入的增加，要想解决所有人的裹腹之需，农民们将需要—如果耕作方式不变—-更多的水源从事生产：据一家研究中心—国际水资源管理研究所(IWMI)预计，2030年的用水量能多灌溉2000立方公里的土地，即比现在的用水量多出四分之一。然而，许多务农区水资源缺乏，并很有可能随着全球变暖的加剧更加缺乏。IWMI的所长Colin Chartres表示，当今世界面临着的是”粮危机”，而不是”水危机”。

The solution, Mr Chartres and others contend, is more efficient use of water or, as the sloganeers put it, “more crop per drop”. Some 1.2 billion people, about a fifth of the world’s population, live in places that are short of water (see map). Farming accounts for roughly 70% of human water consumption. So when water starts to run out, as is happening in northern China, southern Spain and the western United States, among other places, farming tends to offer the best potential for thrift. But governments, whether to win votes or to protect the poor, rarely charge farmers a market price for water. So they are usually more wasteful than other consumers-even though the value they create from the water is often less than households or industry would be willing to pay for it.

应对之道是以Chartres为首的人声称的对水资源更充分的利用，或是标语作者声称的”用一滴水灌溉更多的庄稼”。12亿左右的人口，约占世界人口的五分之一，生活在缺水地区（见上图，图例见这里）。农业用水约占人类总耗水量的70%。所以一旦出现水资源要枯竭的趋势，正如中国北部、西班牙南部和美国西部等其他地区那样，最有可能减少水供应量的往往是务农活动。但是各国政府，或是为了赢得选票，或是为了保护穷人，很少以市场价格向农民收取水费。所以，农民往往比其他使用者浪费更多的水，尽管他们利用水资源创造的价值高于家庭或工业愿意支付的价格。

The pressing need is to make water go further. Antoine Frérot, the head of the water division of Veolia Environnement, a French firm, promotes recycling, whereby city wastewater is treated until it can be used in industry or agriculture. This costs about a third less than desalination, and cuts pollution. He expects his recycling business to quadruple in the next decade.

当务之急是要一水多用。法国Veolia Environnement供水部门负责人Antoine Frérot建议实行水资源循环利用，即对城市废水进行处理，直到其达到可供工农业使用的标准。此举比脱盐减少了三分之一的成本，同时能降低污染。他预计未来十年，水回收业务将翻两番。

Yet as Mr Frérot himself concedes, there are many even cheaper ways to save water. As much as 70% of water used by farmers never gets to crops, perhaps lost through leaky irrigation channels or by draining into rivers or groundwater. Investment in drip irrigation, or simply repairing the worst leaks, could bring huge savings.

然而，就像Frérot承认的那样，更为经济的节水途径还有很多。农民用水的70%并没有用在作物灌溉上，这些水或是流失于漏缝的灌溉渠间，或是渗透到河流和地下。投资滴灌或是简单的修理大的漏缝，都可以节省大量水资源。

Farmers in poor countries can usually afford such things only if they are growing cash crops, says David Molden of IWMI. Even basic kit such as small rainwater tanks can be lacking. Ethiopia, for example, has only 38 cubic metres of storage capacity per inhabitant, compared to almost 5,000 in Australia. Yet modest water storage can hugely improve yields in rain-fed agriculture, by smoothing over short dry spells. Likewise, pumping water into natural aquifers for seasonal storage tends to be much cheaper than building a big dam, and prevents the great waste of water through evaporation.

IWMI的David Molden表示，只要穷国的农民种植经济作物，他们通常就能负担的起上述补救活动。现在，即使是小型储雨水的水箱也不足。例如，埃塞俄比亚每位居民仅能储水38立方米，而澳大利亚是将近5000立方米。然而，少量的储水就能缓解短暂干旱季节的用水紧张，从而大大提高雨养农业的产量。同样，把水抽送到天然地下储水层，季节性地储水，往往也比建大坝省更多的钱，同时还防止水分蒸发的浪费。

Even when water is scarce, it is often squandered. Mr Molden cites the example of cotton-farmers in Uzbekistan, who used to receive a fixed allocation of water for irrigation whether they needed it or not, in a holdover from the days of Soviet central planning. Simply putting farmers in control of the irrigation network, and allowing them to decide how much water they needed, cut consumption by 30%.

即使是在水资源短缺期，农民们浪费现象也经常发生。（对此）Molden引用了乌兹别克斯坦的棉农的例子：过去，无论需要与否，他们都会分到定量的水资源用于灌溉，这是前苏联中央计划经济的配额制度。然而，仅是让农民控制灌溉网，使他们自己决定所需水量，就能减少30%的耗水量。

Cotton paying a high price for water
耗水量很大的棉花

Similarly, rice farmers can sharply cut water consumption by flooding paddy fields only some of the time. Wheat growers in hot places such as India and Australia can conserve water by minimising tilling, leaving a layer of mulch on the fields’ surface to absorb rainwater and limit evaporation. In arid regions like the Middle East, Mark Zeitoun of the London School of Economics suggests substituting thirsty crops such as oranges with more abstemious olives and dates. Ideally, countries that are short of water would concentrate on growing the most valuable cash crops, and use the proceeds to import staples.

同样，稻农只要时不时充分灌溉稻田就可以大幅减少用水量。生活像印度、澳大利亚这样炎热地区的麦农们减少耕作次数，使耕地表面留有的一层枯叶覆盖层，用来吸收雨水，减少蒸发，从而节约灌溉用水。伦敦经济学院的Mark Zeitoun建议，在中东这样的干旱地区，用抗旱的橄榄等作物替代橙子等喜水作物。理想做法是，缺水国家致力于种植最有价值的经济作物，用售后收入进口大宗食品。

Agronomists are beginning to devise tools to help monitor the efficiency of water use. Some have designed algorithms that use satellite data on surface temperatures to calculate the rate at which plants are absorbing and transpiring water. That allows governments and development agencies to concentrate their efforts on the most prodigal areas.

农业学家们开始设计工具，帮助监测水的使用效率。一些人已经设计了各种算法，可利用卫星针对地表温度收集数据，计算出地球吸收和蒸发水分的速率。这使得各国政府和发展机构能够着重改进耗水最严重地区。

But efficient use of water, cautions Pasquale Steduto of the United Nations’ Food and Agriculture Organisation, is just one step to better agricultural yields. Even if farmers use the right amount of water they also need decent seeds and enough fertiliser. In Africa in particular, these and other factors such as pest control, storage and distribution are a bigger drag on yields than a shortage of water.

但是，联合国食品与农业组织的Pasquale Steduto警告说，有效用水只是提高农业产量的其中一步。即使农民用水适量，他们也需要优质的种子和足够的化肥。尤其是在非洲，像虫害防治、粮食储备和分配等这样或那样的因素，比缺水更能影响粮食产量。

Raising yields does not always involve greater water consumption, especially when farms are inefficient. It would take little extra water to double cereal output in many parts of Africa, Mr Molden argues. IWMI reckons that some three-quarters of the extra food the world needs could be provided simply by bringing yields in poor countries closer to those of rich ones. That is more palatable than the puritanical alternative: giving up meat and other thirsty products altogether.

提高产量并不总是意味着加大灌溉力度，尤其是农场效率低下时。Molden称，在非洲的许多地区，要使谷物产量翻番可能只需多消耗很少的水。IWMI预计，只要将穷国的产量提高到接近富国的水平，世界就可多生产四分之三左右的粮食。还一种清教徒式的选择–把包括肉类在内的耗水型产品统统放弃。（不过）这种做法可没有前者那么合理。

译者：mxrruler  http://www.ecocn.org/forum/viewthread.php?tid=14171&extra=page%3D1