Changing glaciers and water supplies in High Mountain Asia

Nearly a billion people in central and southern Asia rely on meltwater from glaciers in mountain ranges including the Himalaya, Karakoram and Hindu Kush, a region known as High Mountain Asia. These glaciers form the headwaters of large rivers including the Indus, Ganges and Brahmaputra, and as such the mountains are often referred to as the ‘water towers of Asia’.

Although much of this region receives substantial precipitation during the Indian summer monsoon, glaciers start to melt a month or two before the monsoon rains begin, so that, even in the monsoon-influenced regions and particularly outside this climate system, the meltwater produced from glaciers each spring buffers the regional water budget and allows farmers to start growing food crops.

Glaciers in High Mountain Asia are shrinking rapidly in response to climate change. As the global climate continues to heat, the rate of glacier loss is accelerating and making water supplies to people living downstream less predictable, while also increasing the risk of glacial hazards. Predicting how glaciers will shrink is important to understanding when glacier meltwater will reach a peak (the fastest ice loss will likely be during the middle of the 21^st Century) and how water supplies vary as the climate continues to warm. Such understanding is required to help policy makers and communities develop strategies to adapt to and mitigate the impacts of climate change for mountain people and the millions living downstream.

Predicting how glaciers will change in response to climate change can be done using computer models that simulate the flow of ice through mountainous terrain and the factors determining how glaciers gain and lose mass. We have been developing these models at Sheffield and collecting field data to ensure that models represent the important processes that control why glaciers change.

Over the last five years, we have carried out fieldwork at the highest glacier on Earth — Khumbu Glacier in the Everest region of Nepal. Staff and students from the Department of Geography have investigated how this large glacier is changing by measuring the temperature of the ice through the glacier using hot-water drilling, and how the glacier has changed in the past by mapping moraines and collecting rock samples to measure the age of these landforms. We have found that Khumbu Glacier is in an advanced state of mass loss and its ice is warmer than the annual air temperature at the same elevation. By using our field observations to train the computer model, we then predict how the glacier will continue to change and the resulting changes in water supplies to rivers that form the headwaters of the Ganges.