Spreading water shortages threaten to reduce the global food supply by more than 10 percent. Left unaddressed, these shortages could lead to hunger, civil unrest, and even wars over water, reports a new book from the Worldwatch Institute.
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," said Sandra Postel, author of Pillar of Sand: Can the Irrigation Miracle Last? The book was funded by the Wallace Genetic Foundation and by the Pew Fellows Program of the Pew Charitable Trusts.
"Some 40 percent of the world's food comes from irrigated cropland," said Postel, "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 civilization is not the first to be faced with the challenge of sustaining its irrigation base," said Postel, director of the Global Water Policy Project in Amherst, Massachusetts, and a senior fellow at the Worldwatch Institute. "A key lesson from history is that most irrigation-based civilizations fail. As we enter the third millennium A.D., the question is: will ours be any 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 the western 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 some 160 billion cubic meters-the amount used to produce nearly 10 percent 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.
Meanwhile, the amount of irrigated land per person is shrinking. It has dropped 5 percent since its peak in 1978, and will continue to fall. At the same time, 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 Ganges in South Asia, and the Colorado in the American Southwest. The Yellow River, the cradle of Chinese civilization, 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...