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Global glacier mass loss to continue on climate change

New Delhi : Mountain glaciers around the globe, considered the largest global freshwater water resources, have responded strongly to recent climate change and are expected to experience continued mass loss and retreat throughout the 21st century.

Worldwide 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 the resulting hydrological consequences have been scarce.

Now, in a new assessment, global glacier runoff changes were computed for 56 large-scale glacierized drainage basins to 2100 and the glacial impact on streamflow was analyzed.

The research, conducted by Matthias Huss of University of Fribourg along with Regine Hock of University of Alaska Fairbanks, found that in roughly half of the investigated basins, the modelled annual glacier runoff continues to rise until a maximum (‘peak water’) is reached, beyond which runoff steadily declines.

In the remaining basins, this tipping point has already been passed. Peak water occurs later in basins with larger glaciers and higher ice-cover fractions. Typically, future glacier runoff increases in early summer but decreases in late summer.

Although most of the 56 basins have less than two per cent ice coverage, by 2100 one-third of them might experience runoff decreases greater than 10 per cent due to glacier mass loss in at least one month of the melt season, with the largest reductions in central Asia and the Andes.

The research, recently published in Nature, concluded that, even in large-scale basins with minimal ice-cover fraction, the downstream hydrological effects of continued glacier wastage can be substantial, but the magnitudes vary greatly among basins and throughout the melt season.

Glacierized large-scale drainage basins cover 26 per cent of the global land surface outside Greenland and Antarctica and are populatedby almost one-third of the world’s population. Melt waters from glaciers contribute to and modulate downglacier streamflow, which affects freshwater availability, hydropower operations, sediment transport and aquatic ecosystems.

Glacier runoff typically shows a distinct seasonality with a minimum in the snow-accumulation season (or dry season in the tropics) and a pronounced maximum in the melt season (or wet season) compared with ice-free basins. Thus, glacier melt water can compensate for seasons and years of otherwise low flow or droughts in lowland areas downstream of glacierized mountain regions, the research noted.

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