A quarter of the world’s population are at risk of water supply problems as mountain glaciers, snow-packs and alpine lakes are run down by global heating and rising demand, according to an international study.

The first inventory of high-altitude sources finds the Indus is the most important and vulnerable “water tower” due to run-off from the Karakoram, Hindu Kush, Ladakh, and Himalayan mountain ranges, which flow downstream to a densely populated and intensively irrigated basin in Pakistan, India, China and Afghanistan.

The authors warn this vast water tower – a term they use to describe the role of water storage and supply that mountain ranges play to sustain environmental and human water demands downstream – is unlikely to sustain growing pressure by the middle of the century when temperatures are projected to rise by 1.9C (3.42F), rainfall to increase by less than 2%, but the population to grow by 50% and generate eight times more GDP.

Strains are apparent elsewhere in the water tower index, which quantifies the volume of water in 78 mountain ranges based on precipitation, snow cover, glacier ice storage, lakes and rivers. This was then compared with the drawdown by communities, industries and farms in the lower reaches of the main river basins.

The study by 32 scientists, which was published in the Nature journal on Monday, confirms Asian river basins face the greatest demands but shows pressures are also rising on other continents.

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