JOIN USDue to natural reasons like glacial melting, the four countries would lose almost 275 billion cubic metres of annual renewable water in the next two decades, more than the total amount of available water in Nepal at present, India-based Strategic Foresight Group said in a report.
"What we are looking at here is a major catastrophe ... going to happen in 20, 25 years," the group's president, Sundeep Waslekar, told a seminar at the Singapore International Water Week.
Water scarcity and effects like desertification and soil erosion would bring rice and wheat yields in China and India down by as much as 50 percent by 2050, the report said.
"China and India alone will need to import more than 200 to 300 million tonnes of wheat and rice," it said.
"This will create a havoc in the global food market ... for people everywhere, because the prices will go up substantially," Waslekar said.
Water depletion in the river basins would displace millions of people in the four countries by 2050, he said.
"We are looking towards a disaster of more than 100 million migrants," he said, "and conflicts within and between countries."
The report called for more cooperation between the four nations in the management of the river basins.
The basins of the rivers, including the Yellow River and the Yangtze in China and the Ganges in India, are home to 1.3 billion people.