单选题 Most people may drink only two liters of water a day, but they consume about 3000 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 need a great deal more water to keep everyone fed: 2000 more cubic kilometers a year by 2030, according to the International Water Management Institute (IWMI). 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.
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 live in places that are short of water. Farming accounts for roughly 70% of human water consumption. So when water starts to run out, farming tends to offer the best potential for thrift. But governments 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.
The pressing need is to make water go further. Antoine Frérot, the head of the water division of Veolia Environment, promotes recycling of city wastewater to be used in industry or agriculture. This costs less and cuts pollution.
Yet as Mr. Fr6rot 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.
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 meters of storage capacity per inhabitant, compared to almost 5000 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.
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.
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 realistic than the absolute alternative: giving up meat and other thirsty Products altogether.
[A] cultivating cash crops
[B] leaking irrigation system
[C] expenses and efficiency
[D] surface temperature data
[E] low water price
[F] water shortage
[G] food crisis

单选题 The world is meeting with challenges more from

单选题 Farmers waste more water due to

单选题 Farmers in poor countries can pay for irrigation improvement by

单选题 Building big dams is less effective for their

单选题 The water use rate of plants is computed with