Melting glaciers around the world will result in reduced downstream water resources even in basins with low ice coverage, reports a paper published online this week in Nature Climate Change.

Glacier retreat and associated future runoff changes raise major concerns over the sustainability of global water resources, but global-scale assessments of glacier decline and resulting hydrological consequences are scarce.

Matthias Huss and Regina Hock investigate changes in monthly and annual glacier runoff for all 56 large-scale glaciated basins, excluding Greenland and Antarctica, to 2100. The authors show that 45% of the studied basins, typically those with smaller glaciers, have already passed maximum annual runoff - or ‘peak water’ - after which runoff steadily declines. For the remaining basins with greater ice cover and larger glaciers, peak water will occur later. The authors also find reductions in total glacier volume ranging from 43%±14 for a low emission scenario to 74±11% for a high emission scenario. The change in associated runoff is variable, with an average increase until peak water of 26% (low emission scenario) to 36% (high emission scenario), with runoff predicted to increase past 2050 for 22% of the basins.

The authors consider the monthly variability of runoff as this will impact on water resources for local communities. They show that by end of the century, a third of the basins may have a 10% or higher reduction in runoff in at least one melt-season month, with central Asia and the Andes seeing the greatest declines. These findings highlight that continued decline in glaciers could have substantial impacts on local water resources.