Raising Water Productivity

by Dave

Earth Policy Institute: Sustainablog

With water shortages emerging as a constraint on food production growth, the world needs an effort to raise water productivity similar to the one that nearly tripled land productivity during the last half of the twentieth century. Worldwide, average irrigation water productivity is now roughly 1 kilogram of grain per ton of water used. Since it takes 1,000 tons of water to produce 1 ton of grain, it is not surprising that 70 percent of world water use is devoted to irrigation. Thus, raising irrigation efficiency is central to raising water productivity overall.

In surface water projects—that is, dams that deliver water to farmers through a network of canals—crop usage of irrigation water never reaches 100 percent simply because some irrigation water evaporates, some percolates downward, and some runs off. Water policy analysts Sandra Postel and Amy Vickers found that “surface water irrigation efficiency ranges between 25 and 40 percent in India, Mexico, Pakistan, the Philippines, and Thailand; between 40 and 45 percent in Malaysia and Morocco; and between 50 and 60 percent in Israel, Japan, and Taiwan.” Irrigation water efficiency is affected not only by the type and condition of irrigation systems but also by soil type, temperature, and humidity. In hot arid regions, the evaporation of irrigation water is far higher than in cooler humid regions.

Raising irrigation water efficiency typically means shifting from the
less efficient flood or furrow system to overhead sprinklers or drip
irrigation, the gold standard of irrigation efficiency. Switching from
flood or furrow to low-pressure sprinkler systems reduces water use by
an estimated 30 percent, while switching to drip irrigation typically
cuts water use in half. A drip system also raises yields because it
provides a steady supply of water with minimal losses to evaporation.
Since drip systems are both labor-intensive and water-efficient, they
are well suited to countries with a surplus of labor and a shortage of
water.

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