In a unique study, scientists have assessed the Earth’s great 78 mountainous regions or the “water towers” and ranked them as per their importance. These towers can generate and then store vast quantities of water.
These “water towers” deliver water in a controlled way to the major populations that live downstream.
According to the Dutch-led team, Asia’s Indus basin is fed by the Himalayan, Karakoram, Hindu-Kush, and Ladakh ranges. These belong to the most critical storage unit on the planet.
More than 200 million people living across parts of Afghanistan, China, India, and Pakistan rely on its waters, produced at a high elevation from snow and rain that drain from lakes and glaciers.
But the researchers warned, the Indus water tower is also the most vulnerable on their list of 78.
Nowadays, a range of current and future pressures for more drinking water, for increased irrigation and industry and other factors could severely curtail supply. The most obvious threat is climate change. Global warming will disrupt precipitation patterns and denude glaciers of their storage capacity. There are also geopolitical tensions, such as the Indus intersects national boundaries.
Media caption of Prof Walter Immerzeel says: “Our data can underpin mountain-specific policies and water treaties.”
“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.
Before the largest annual gathering of Earth scientists at the American Geophysical Union’s Fall Meeting, Dr Bolch addressed the issue. The work of his team is being published simultaneously in the journal Nature.
After conducting the assessment across the major continents, the team identified the five most relied-upon natural water tower systems in those regions:
- Asia: Indus, Tarim, Amu Darya, Syr Darya, Ganges-Brahmaputra
- Europe: Rhône, Po, Rhine, Black Sea North Coast, Caspian Sea Coast
- North America: Fraser, Columbia and Northwest United States, Pacific and Arctic Coasts, Saskatchewan-Nelson, North America-Colorado
- South America: South Chile, South Argentina, Negro, La Puna region, North Chile
The study does not include Africa in this listing, principally because it is devoid of significant glacier systems. In places such as on Mount Kilimanjaro and Mount Kenya of this continent, there are ice bodies, but their contribution to downstream catchments is limited.
The remarkable aspect of the towers is the way they maintain essential water supplies to populations. They supply water even when there is a drought in summer months with the steady melt of high-elevation ice.
The study made it clear that the Asian towers are more vulnerable compared to the rest of the world. This is because the projected future demand will be much higher due to the population growth in Asia compared to Europe.
There are also specific political stresses in Asia that will challenge the future reliability of towers.
For instance, the waters of the Amu Darya and Syr Darya river basins again sourced from high-mountain glaciers run through low-precipitation areas where the competition for irrigation for agricultural activities is intense. The much-reduced size of the Aral Sea is evidence of this, which is ultimately fed by both the rivers.
“What we recommend in our study is that we should really recognize mountains as global assets of the Earth system, and that means mountain ranges should be at the top of political agendas, and dedicated policies should be developed,” co-team leader Prof Walter Immerzeel from Utrecht University said.
“We are only the scientists; we put out the numbers. But we’ve got very much better at that over the past two decades, so we can give really specific scientific background that can help for example to develop water treaties. We can aid the process.”
Dr Bethan Davies, a team-member from Royal Holloway, University of London, commented: “I think when we’ve talked about climate change and ice loss, a lot of the narrative has been around sea-level rise. But actually over the next 100 years, climate change is going to affect drinking water for people, water for power, water for agriculture – and in these water towers, we’re talking about the supply to about 1.9 billion people. That accounts for more than 20% of the world’s population.
“We need to adopt urgent mitigation strategies or we will face severe water shortages,” she told BBC News.
National Geographic and Rolex supported the study “water towers” as part of their Perpetual Planet partnership, which is a portal that allows users to explore the data and compare tower rankings.