(The Ecologist) In an exclusive extract from his new book, World on the Edge, Lester Brown outlines fresh ways of thinking about water and land use in order to sustain the world’s growing population
Prior to 1950, growth of the food supply came almost entirely from expanding cropland area. Then as frontiers disappeared and population growth accelerated after World War II, the focus quickly shifted to raising land productivity. In the most spectacular achievement in world agricultural history, farmers doubled the grain harvest between 1950 and 1973. Stated otherwise, growth in the grain harvest during this 23-year-span matched that of the preceding 11,000 years.
This was the golden age of world agriculture. Since then, growth in world food output has been gradually losing momentum as the backlog of unused agricultural technology dwindles, as soil erodes, as the area of cultivable land shrinks, and as irrigation water becomes scarce.
With water shortages constraining food production growth, the world needs a campaign to raise water productivity similar to the one that nearly tripled land productivity over the last half-century. Data on the efficiency of surface water projects-that is, dams that deliver water to farmers through a network of canals-show that crops never use all the irrigation water simply because some 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.’
China’s irrigation plan is to raise efficiency from 43 percent in 2000 to 55 percent in 2020. Key measures include raising the price of water, providing incentives for adopting more irrigation-efficient technologies, and developing the local institutions to manage this process. Raising irrigation efficiency typically means shifting from the less-efficient flood or furrow systems to over- head sprinklers or to 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.
Drip irrigation also raises yields because it provides a steady supply of water with minimal losses to evaporation. In addition, it reduces the energy needed to pump water. 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. A few small countries-Cyprus, Israel, and Jordan-rely heavily on drip irrigation. This more-efficient technology is used on 1-3 percent of irrigated land in India and China and on roughly 4 percent in the United States.
In recent years, small-scale drip-irrigation systems- literally an elevated bucket with flexible plastic tubing to distribute the water-have been developed to irrigate small vegetable gardens with roughly 100 plants (covering 25 square meters). Somewhat larger systems using drums irrigate 125 square meters. In both cases, the containers are elevated slightly so that gravity distributes the water. Large-scale drip systems using plastic lines that can be moved easily are also becoming popular. These simple systems can pay for themselves in one year. By simultaneously reducing water costs and raising yields, they can dramatically raise incomes of smallholders. Sandra Postel of the Global Water Policy Project estimates that drip technology has the potential to profitably irrigate 10 million hectares of India’s cropland, nearly one tenth of the total. She sees a similar potential for China, which is now also expanding its drip irrigated area to save scarce water.
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. Farmers in many countries are organizing 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. Mexico is a leader in developing water users associations. As of 2008, farmers associations managed more than 99 percent of the irrigated area held in public irrigation districts. One advantage of this shift is that the cost of maintaining the irrigation system is assumed locally, reducing the drain on the treasury.
15th February, 2011
by Lester Brown