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Himalayan glacier melting threatens water security for millions of people

Large bodies of ice are losing mass faster than they are accumulating it

MOUNTAIN MELT Melting glacier water feeds the Indus River, shown in this photo at its confluence with the Zanskar River in the Himalayan region of Ladakh.

Meltwater from glaciers in Asia’s high mountain ranges, including the Himalayas, meets the basic water needs of about 221 million people each year. But that store of freshwater is shrinking, a study finds, threatening regional water security within just a few decades.

Glaciers can store water for decades or even centuries before releasing it into rivers, providing a steady supply to sustain downhill populations even in times of drought, writes glaciologist Hamish D. Pritchard of the British Antarctic Survey in Cambridge.

But glaciers in the mountains are melting faster than they can be replenished by snowfall, Pritchard reports in the study, published online May 29 in Nature. To estimate the extent of the imbalance, Pritchard calculated summertime meltwater volumes and winter snowfall rates using a range of datasets, including altitude-adjusted precipitation and temperature records from 1951 to 2007, as well as observed changes in glacier volumes from 2000 to 2016.

Based on those data, the overall volume of meltwater rushing down the mountains each year from 2000 to 2016 was 1.6 times as much as it would have been if the system were in balance.

As the global average temperature continues to increase, summertime glacial melt will continue to outpace snowfall, shrinking the glaciers — until eventually, runoff from the mountains tapers off, Pritchard notes. If countries fail to rein in greenhouse gas emissions, the annual meltwater flowing into the region’s rivers could be noticeably decreased by 2090.

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