CLIMATE change and growing demand threaten the water supply for billions of people, an international study has found.

St Andrews University expert Dr Tobias Bolch was amongst more than 30 scientists to piece together an in-depth analysis of natural water systems around the globe.

The 78 systems rely on mountain glaciers and supply resources to almost two billion people – around one quarter of the global population.

But the loss of ice and snow on high mountains due to warming temperatures is now hitting these systems, it is claimed.

Meanwhile, demand in some of the most vulnerable areas, including those supplied by the Himalayas, continues to grow.

The study – the first of its kind – named the Indus basin, which is made up of vast sections of this mountain range, as the most relied-upon system of its kind.

It delivers water to areas of Afghanistan, China, India and Pakistan. Bolch, of the School of Geography and Sustainable Development at St Andrews University, said: “The study quantified for the first time the natural water supply from mountains and the water demand by society, providing projections based on climatic and socioeconomic scenarios.

“The projected loss of ice and snow and increasing water needs makes specific densely-populated basins located in arid regions, like the Indus basin in South Asia or the Amu Darya basin in Central Asia, highly vulnerable in the future.”

The systems, known as mountain water towers, store and transport water via glaciers, snow packs, lakes and streams. In Europe, the Rhone water tower is the most important, while in North America the Fraser water tower is in first place, with the South Chile tower the most relied-upon in South America.

The research, published in Nature, also names the mismanagement of water resources and other geopolitical factors as threats to future supplies.

To combat this, the authors call for the development of “international, mountain-specific conservation and climate change adaptation policies and strategies to safeguard both ecosystems and people downstream”.

Professor Walter Immerzeel of Utrecht University, one of the two study leaders, commented: “What is unique about our study is that we have assessed the water towers’ importance, not only by looking at how much water they store and provide, but also how much mountain water is needed downstream and how vulnerable these systems and communities are to a number of likely changes in the next few decades.”

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Co-leader Dr Arthur Lutz went on: “By assessing all glacial water towers on Earth, we identified the key basin that should be on top of regional and global political agendas.”

This research was supported by National Geographic and Rolex as part of their Perpetual Planet partnership, which also sponsors international expeditions and cutting-edge technologies.

Jonathan Baillie, chief scientist at the National Geographic Society, said: “Mountains are iconic and sacred places around the world, but the critical role they play in sustaining life on Earth is not yet very well understood.

“This research will help decision-makers prioritise where action should be taken to protect mountain systems, the resources they provide, and the people who need them.”