Glacial change and hydrological implications in the Himalaya and Karakoram

Glaciers in the Himalaya-Karakoram mountain ranges harbour approximately half of the ice volume in High-mountain Asia and modulate the flow of freshwater to almost 869 million people within the Indus, Tarim, Ganges and Brahmaputra river basins. Since the mid-twentieth century, rising temperatures have led to unsustainably high melting rates for many glaciers, particularly in the Himalaya, temporarily increasing summer meltwater run-off but continuously reducing the ice-storage volume. In this Review, we discuss how and why glaciers and meltwater supplies have changed, how they will likely evolve in the future and how these changes impact water resources and water-related hazards. Heterogeneous glacier retreat is changing streamflow patterns, in turn, affecting the incidence of glacial-lake outburst floods and exacerbating the risk of flooding and water shortages associated with future climate change. These changes could negatively impact downstream populations and infrastructure, including the thriving hydropower sector and some of the world's largest irrigated agriculture systems, by making water flow more extreme and unpredictable. An improved in situ monitoring network for weather, hydrology and glacier change is a crucial requirement for predicting the future of this resource and associated hazards, and their impact on regional water, energy and food security. Glaciers in the Himalaya and Karakoram mountain ranges provide freshwater and hydropower to millions of people but are also melting at unsustainably high rates. This Review discusses recent and projected changes in glacier melt and resulting implications for regional water-related hazards and water resources. Key pointsHimalayan glaciers have lost mass at an accelerating rate in recent decades, in contrast with relatively stable Karakoram glaciers.Under a range of climate change scenarios, the run-off of glacier meltwater in the Himalaya and Karakoram is likely to peak in the next few decades.After glacial run-off peaks, run-off will decline as the glaciers in both mountain ranges shrink, although the magnitude and timing of the peak and the rate of subsequent decline are uncertain.Basin run-off regimes will become more rain-dominated as the modulating effect of glaciers decreases, and this is likely to increase the impact of droughts and floods.The frequency of glacial-lake outburst floods and run-off floods have increased recently and could increase further in coming decades, threatening existing and planned hydropower infrastructure downstream.A lower-emissions climate change pathway would reduce the rate of glacier loss, increasing the time available for adaptation. This pathway would have considerable socio-economic benefits.

Automated summary

Glaciers in the Himalaya-Karakoram mountain ranges provide freshwater and hydropower to millions of people, but they are melting at unsustainably high rates. Recent decades have seen accelerated mass loss in Himalayan glaciers, contrasting with relatively stable Karakoram glaciers. Under various climate change scenarios, glacier meltwater run-off in the two mountain ranges is expected to peak in the next few decades, followed by a decline as the glaciers shrink.