Climate change: 1.9 billion people rely on natural 'water towers' - BBC News
A new study ranks the importance and vulnerability of high-mountain stores of water.
These are the 78 mountainous regions that are able to generate and then store vast quantities of water.
They deliver it in a controlled way to major populations living downstream.
The Dutch-led team finds Asia's Indus basin - fed by the Himalayan, Karakoram, Hindu-Kush, and Ladakh ranges - to be the most important storage unit on the planet.
Its waters, produced at high elevation from rain and snow, and draining from lakes and glaciers, support more than 200 million people settled across parts of Afghanistan, China, India and Pakistan.
But the Indus water tower, the researchers point out, is also the most vulnerable on their list of 78.
It's subject to a range of current and future pressures, from ever greater demand - for more drinking water, for increased irrigation and industry, etc - to issues that could severely curtail supply. The latter will include geopolitical tensions, given the Indus intersects national boundaries; but the most obvious threat is climate change. A warming world will disrupt precipitation patterns and denude glaciers of their storage capacity.
"If, basically, the demand is higher but the supply decreases, then we really have a problem," said research team-member Dr Tobias Bolch from the University of St Andrews, UK.
"And this is, I think, one of the major strengths of our study - that we have looked closely at both sides, so the supply index and the demand index," he told BBC News.
Dr Bolch is speaking here at the American Geophysical Union's Fall Meeting, the largest annual gathering of Earth scientists. His and colleagues' work is being published simultaneously in the journal Nature.