Low prices of water and drop in productivity

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: 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 second half of the twentieth century. Worldwide, average irrigation water productivity is now roughly one kg of grain per tonne of water used. Since it takes 1,000 tonne of water to produce one tonne of grain, it is not surprising that 70% 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% 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% in India, Mexico, Pakistan, the Philippines and Thailand; between 40% and 45% in Malaysia and Morocco; and between 50% and 60% 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%, 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 labour-intensive and water-efficient, they are well suited to countries with surplus labour and warer shortage.

A few small countries—Cyprus, Israel, and Jordan—rely heavily on drip irrigation. Among the big three agricultural producers, this more-efficient technology is used on 1-3% of irrigated land in India and China and on roughly 4% in the US.

In recent years, small-scale drip-irrigation systems—virtually a bucket that relies on gravity to distribute the water through flexible plastic tubing—have been developed to irrigate small vegetable gardens with roughly 100 plants (covering 25 sq mt). Somewhat larger drum systems irrigate 125 sq mt. Large-scale drip systems that can be moved easily are also becoming popular. These simple systems can pay for themselves in one year. By reducing water costs and raising yields, they can dramatically raise incomes of smallholders.

Sandra Postel estimates that the combination of these drip technologies at various scales has the potential to profitably irrigate 10 million hectares of India’s cropland, or nearly one-tenth of the total. In Punjab, fast-falling water tables led the state farmers’ commission in 2007 to recommend a delay in transplanting rice from May to late June or early July. This would reduce irrigation water use by roughly one-third since transplanting would coincide with the arrival of the monsoon. This reduction in groundwater use would help stabilise the water table, which has fallen from 5 metre below the surface to 30 metres in parts of the state.

Institutional shifts—specifically, moving the responsibility for managing irrigation systems from government agencies to local water users associations—can facilitate the more efficient use of water. In many countries farmers are organising locally so they can assume this responsibility, and since they have an economic stake in good water management, they tend to do a better job than a distant government agency.

Low water productivity is often the result of low water prices. In many countries, subsidies lead to irrationally low water prices, creating the impression that water is abundant when, in fact, it is scarce. As water becomes scarce, it needs to be priced accordingly. Provincial governments in northern China are raising water prices in small increments to discourage waste. A higher water price affects all water users, encouraging investment in more water-efficient irrigation technologies, industrial processes, and household appliances.

What is needed now is a new mindset, a new way of thinking about water use. For example, shifting to more water-efficient crops wherever possible boosts water productivity. Rice production is being phased out around Beijing because rice is a thirsty crop. Egypt also restricts rice production. Any measures that raise crop yields on irrigated land also raise the productivity of irrigation water. Any measures that convert grain into animal protein more efficiently in effect increase water productivity.

For people consuming unhealthy amounts of livestock products, moving down the food chain reduces water use. In the US, where annual consumption of grain as food and feed averages some 800 kg (four-fifths of a tonne) per person, a modest reduction in the consumption of meat, milk and eggs could easily cut grain use per person by 100 kg. For 300 million Americans, such a reduction would cut grain use by 30 million tonne and irrigation water use by 30 billion tonne.

Reducing water use to the sustainable yield of aquifers and rivers worldwide involves a wide range of measures not only in agriculture but throughout the economy. The more obvious steps, in addition to those mentioned here, include adopting more water-efficient industrial processes and using more water-efficient household appliances. Recycling urban water supplies is another obvious step to consider in countries facing acute water shortages.