Spreading water shortages are threatening to reduce the global food supply by more than 10 per cent. Left unaddressed, these shortages could lead to hunger, civil unrest, and even wars over water. Irrigation accounts for two-thirds of global water use, but less than half that water reaches the roots of plants. "Without increasing water productivity in irrigation, major food-producing regions will not have enough water to sustain crop production," says Sandra Postel, the author. Some 40 per cent of the world's food comes from irrigated cropland, and we're betting on that share to increase to feed a growing population. But the productivity of irrigation is in jeopardy from the overpumping of groundwater, the growing diversion of irrigation water to cities, and the buildup of salts in the soil.
"Our civilisation is not the first to face the challenge of sustaining its irrigation base," says Postel, director of Global Water Policy Project in Amherst, Massachusetts, and a senior fellow at Worldwatch Institute. "A key lesson from history is that most irrigation-based civilisations fail. As we enter the third millennium, the question is: will our's be different?" Today, irrigation problems are widespread in the grain-growing regions of central and northern China, northwest and southern India, parts of Pakistan, much of west United States, North Africa, the Middle East, and the Arabian Peninsula.
Water tables are dropping steadily in several major food-producing regions as groundwater is pumped faster than nature replenishes it. The world's farmers are racking up an annual water deficit of 160 billion cubic metres-the amount used to produce 10 per cent of the world's grain. The overpumping of groundwater cannot continue indefinitely. Eventually the wells run dry, or it becomes too expensive to pump from greater depths.
With water so scarce and unpredictable, farmers in the lower stretches of canal networks plant less-risky crops and apply less fertiliser. As a result, yields decline from head to tail, and so do farmers' incomes. One study in India found that irrigators near the head of the canal system earned six times as much as those in the tail. It was estimated that 25 to 40 per cent of the area declared irrigated in India suffers from tail-end deprivation. The lost productivity, reduced income, increased inequity, and resource degradation caused by the skewed distribution of water in canal systems make the tailender issue one of the most serious unsolved problems in irrigation.
The amount of irrigated land per person worldwide is shrinking as well. It has dropped 5 per cent since its peak in 1978, and will continue to fall. And one in five hectares of irrigated land is damaged by salt-the silent scourge that played a role in the decline of ancient Mesopotamian societies. So much water is being diverted for irrigation and other human uses that many major rivers now run dry for large portions of the year-including the Yellow in China, the Indus in Pakistan, the Ganga in South Asia, and the Colorado in the American Southwest. The Yellow river, the cradle of Chinese civilisation, ran dry for a record period in 1997, failing to reach the sea for 226 days.
With population growing rapidly in many of the most water-short regions, water problems are bound to worsen. The number of people living in water-stressed countries is projected to climb from 470 million to 3 billion by 2025, the study notes. Already many countries do not have enough water to meet domestic demands for food, creating a source of potential political instability.
Farmers in India face mounting competition over water. India will add 340 million people to its cities between 1995 and 2025, more than the current populations of the United States and Canada combined. Reallocations are reportedly occurring to increase supplies for the cities of Madras, Coimbatore, and Tirupur and for a number of smaller towns. The textile town of Tirupur in Tamil Nadu, suffers from a water deficit of 22 million cubic metres a year and serious degradation of water quality, and has begun to import more water from outside the city. Many farmers within 35 kilometres of the city have abandoned farming and instead sell their groundwater to urban and industrial users.
Water-short countries are increasingly turning to the world grain market. In the swathe of countries from Morocco across North Africa and the Middle East to Iran, virtually every nation is facing water shortages as rising populations draw against a limited supply and as irrigation water is diverted to satisfy growing urban demand. To meet their food needs, these countries are importing grain. Importing a ton of wheat is the equivalent of importing 1,000 tonnes of water.
Last year, the water required to produce the grain and other farm products imported into the region was equal to the annual flow of the Nile river. And this deficit is growing year after year. "As water shortages continue to mount, it is dangerous to presume, as many officials do, that there will be enough exportable grain to meet the import needs of all these countries at a price they can afford," says Postel. "Most of the growth in water-stressed populations will be in South Asia and sub-Saharan Africa."
In five of the world's hot spots of water dispute-the Aral Sea region, the Ganga, the Jordan, the Nile, and the Tigris-Euphrates-the population of the nations within each basin is projected to climb between 44 and 75 per cent by 2025. Some 260 rivers flow through two or more countries, but in most cases there is no treaty among all the parties that sets out how that river water should be shared. In the absence of water-sharing agreements, tensions are bound to rise.
Irrigation's heavy water demands are also damaging the health of the aquatic environment-shrinking wetlands, reducing fish populations, and pushing species toward extinction. "Using water as inefficiently as we do today, meeting the food demands of the projected 8 billion people in 2030 would result in costly losses of ecological services that the economy depends upon," Postel says.
In India, 7 million hectares are estimated to be losing productivity because of salt buildup, and the problem is worsening. About 36 percent of the affected land lies in the plains of the Indus and Ganges Rivers, including portions of the agriculturally important states of Haryana, Punjab, Madhya Pradesh, and Uttar Pradesh. In Haryana, for example, which is an important breadbasket for India, the 15 billion cubic metres of water delivered by canal each year brings in more than 2 million tons of salt. Over an area of about 400,000 hectares, the water table has risen to within 3 metres of the surface -- dangerously high. If corrective actions are not taken, this high-water-table zone threatens to spread to 2 million hectares of farmland.19
To meet the challenges of a water-short world, Postel proposes a "Blue Revolution" to dramatically boost water productivity. "Most farmers today irrigate the way their predecessors did hundreds of years ago," says Postel. "Just as raising land productivity helped meet food needs during the last half of this century, boosting water productivity will be the agricultural frontier during the next century. The challenge today is to substitute technology and better management for water."
In India, disappointing results from many large-scale irrigation projects along with mounting opposition to the construction of large dams is rekindling interest in a rich variety of traditional, precolonial irrigation practices. These various water harvesting methods developed over the centuries to enable villagers to cope with large seasonal differences in rainfall. India gets 80 percent of its precipitation in three to four months, making rain-fed crop production during the other eight to nine months highly risky. The diversity of water harvesting methods that evolved matches the diversity of India's ecological conditions and cultural traditions, and many have withstood the test of considerable stretches of time. Postel cites the instance of the havelis of Madhya Pradesh and the eris of Tamil Nadu.
Postel describes a diverse and creative mix of "Blue Revolution" strategies. She cites the instance of farmers in countries as diverse as India, Israel, Jordan, Spain and the US cutting their water use by 30 to 70 per cent and raised crop yields by 20 to 90 per cent by using drip irrigation systems that deliver water directly to crop roots.
She says in the Texas high plains, farmers using highly efficient sprinklers raised their water efficiency to more than 90 per cent while simultaneously increasing corn yields by 10 per cent and cotton yields by 15 per cent. Rice farmers in Malaysia saw a 45 per cent increase in their water productivity through a combination of better scheduling their irrigation, shoring up canals, and sowing seeds directly in the field rather than transplanting seedlings. Israel is now reusing 65 per cent of its domestic wastewater for crop production, freeing up additional freshwater for households and industries.
Postel shows that a special effort is needed to lift the water productivity of millions of very poor farmers who cannot afford some of the more advanced technological solutions. "Helping small-scale farm families raise their incomes and improve their food security can be a powerful engine of economic growth in the world's poorest regions," she says. In Kenya, Chad, Zambia and India, farmers are combining indigenous water-management techniques with inexpensive new technologies like low-cost sprinklers, bucket-drip systems, small-scale pumps, and check dams.
For the "Blue Revolution" to succeed, Postel says, it is up to governments and water authorities to adopt new rules of the game for irrigation. Government subsidies totalling at least $33 billion a year make it cheaper to waste water than to conserve it. Legal barriers often make it difficult for farmers to sell any water they save through conservation practices. And the failure to regulate groundwater overpumping leaves the world vulnerable to sudden cutbacks in food production as water tables drop to greater and greater depths.
