A bull grazes on dry wheat husks(Phi) in Logan, Kansas, one of the regions hit by the record drought that has affected more than half of the U. S. and is expected to drive up food prices. Leading water scientists have issued one of the sternest warnings yet about global food supplies, saying that the world's population may have to switch almost completely to a vegetarian diet over the next 40 years to avoid catastrophic shortages. Adopting a vegetarian diet is one option to increase the amount of water available to grow more food in an increasingly climate-unstable world, the scientists said. Animal protein-rich food consumes 5 to 10 times more water than a vegetarian diet. One third of the world's arable( 适于耕种的 ) land is used to grow crops to feed animals. Other options to feed people include eliminating waste and increasing trade between countries in food surplus and those in deficit. "900 million people already go hungry and 2 billion people are malnourished in spite of the fact that per capita food production continues to increase," they said. "With 70% of all available water being in agriculture, growing more food to feed an additional 2 billion people by 2050 will place greater pressure on available water and land. " The report is being released at the start of the annual world water conference in Stockholm, Sweden, where 2,500 politicians, UN bodies, non-governmental groups and researchers from 120 countries meet to address global water supply problems. Competition for water between food production and other uses will intensify pressure on essential resources, the scientists said. "The UN predicts that we must increase food production by 70% by mid-century. This will place additional pressure on our already stressed water resources, at a time when we also need to allocate more water to satisfy global energy demand—which is expected to rise 60% over the coming 30 years—and to generate electricity for the 1.3 billion people currently without it," said the report. Overeating, undernourishment and waste are all on the rise and increased food production may face future constraints from water scarcity. "We will need a new recipe to feed the world in the future," said the report's editor, Anders Jagerskog. A separate report from the International Water Management Institute (IWMI) said the best way for countries to protect millions of farmers from food insecurity in sub-Saharan Africa and south Asia was to help them invest in small pumps and simple technology, rather than to develop expensive, large-scale irrigation projects. "Farmers across the developing world are increasingly relying on and benefiting from small-scale, locally-relevant water solutions. These techniques could increase yields up to 300% and add tens of billions of U. S. dollars to household revenues across sub-Saharan Africa and south Asia. " said Dr. Colin Chartres, the director general.