Chronic water shortages may appear during the 1990s from northern China to the western United States, said a global report on irrigation released Saturday.
The report - "Water for Agriculture: Facing the Limits" - said changes in world temperature almost inevitably will change the patterns of rain and water supply for several decades.That would make it harder for farmers to grow enough food for the world's rising population, said the author, Sandra Postel, at a briefing Thursday on the report.
Postel is vice-president of Worldwatch Institute, a study group supported by private foundations and United Nations agencies.
"Many areas could enter a period of chronic shortages during the nineties, including northern China, virtually all of northern Africa, pockets of India, Mexico, much of the Middle East, and parts of the western United States," she wrote.
"Where scarcities loom, cities and farms are beginning to compete for available water; when water supplies tighten, farmers typically lose out," she wrote.
She quoted one study as showing that global warming in the west could change the flow of melting snow from the Rocky Mountains, taking 11 million acres of irrigation.
Other reasons for shortages include over-pumping of water from supplies under the surface, poor management of reservoirs and - most important - the rapid growth of population the Third World.
Her expectation of changes due to global warming was challenged as speculative by Mark Rosegrant, an irrigation expert at the International Food Policy Research Institute. He suggested that her predictions may be too pessimstic.
In an interview, he suggested that the right policy by governments, including higher prices for water, could improve water supplies.
But he agreed with her that irrigation will not increase much in the 1990s.
Postel cited Egypt, heavily dependent on aid from the United States and on water from the Nile, as a prime candidate for a disastrous water shortage that could reduce the already low living standards of its 55 million people.