Glaciers in the high mountains of Asia play an important but underappreciated part in protecting populations that live downstream from the effects of droughts, according to a study in this week’s Nature. Meltwater from these glaciers during the summer yield enough water to fulfil the basic needs of 136 million people, or most of the annual municipal and industrial needs of Pakistan, Tajikistan, Turkmenistan, Uzbekistan and Kyrgyzstan.
The high-mountain region of Asia has the highest concentration of mountain glaciers in the world and 800 million people are at least partly dependent on their meltwater. The meltwater produced from glacial ice can act to protect against extreme water shortages and during drought summers, meltwater dominates water inputs to the upper Indus and Aral river basins. However, there are very few direct measurements of glacial mass balance (the difference between the gain and loss of mass of a glacier), and the importance of meltwater from glaciers during droughts has not been comprehensively assessed.
Hamish Pritchard estimated basin-wide multi-decadal glacier mass balance and, by combining this with average and drought precipitation data, quantified the contribution of glaciers to basin water inputs. The author found that, in total, the glaciers of high-mountain Asia yield a net 23 cubic kilometres of water each summer. Without these glaciers, summer monthly water inputs in an average year would be reduced by up to 38% in the upper Indus basin, and by up to 58% in drought conditions; in the upper Aral basin, lost summer water inputs would frequently reach 100%.