Himalayan ice is stable, but Asia faces drought

Shanta Barley in New Scientist: The Himalayan glaciers that feed Asia's five largest rivers are in no danger of disappearing by 2035, as claimed in the Intergovernmental Panel on Climate Change's most recent report. In fact, only the glaciers that melt into the Ganges are shrinking, according to the most detailed analysis yet of how climate change will affect key Asian glaciers.

The aim of the study was to determine how rising carbon dioxide levels will affect Asia's "water towers" – the glaciers whose meltwater supplies drinking and irrigation water to 1.4 billion people. And although the glaciers are safe for now, the study warns of drought to come: the five rivers will be able to water crops for almost 60 million fewer mouths by 2050.

Walter Immerzeel of Utrecht University in the Netherlands used data from a pair of satellites known as GRACE to estimate changes in the thickness of the glaciers that supply the Indus, Brahmaputra, Ganges, Yangtze and Yellow rivers between 2001 and 2007. He found that only the 100-metre-thick glaciers that feed the Ganges are thinning, at a rate of 22 centimetres per year.

…Until now, it has been unclear how much Asia's rivers rely on melting glaciers. Immerzeel fed his GRACE data on ice cover, as well as temperature and rainfall data gathered between 2001 and 2007, into a standard model of river flow.

The model shows that the Indus and the Brahmaputra rely most on glaciers: meltwater accounts for 60 per cent of water carried by the Indus and 20 per cent of that in the Brahmaputra, but less than 10 per cent of the Ganges, Yangtze and Yellow rivers comes from melted ice. Rainfall makes up the rest.

These results would suggest that the Indus and Brahmaputra will be hardest hit by climate change – but taking into account changes in rainfall patterns with climate change causes a different pattern to emerge, says Immerzeel….

The Brahmaputra River, seen from the SPOT satellite back in 2006