Satellite images are making the fate of the Himalayan glaciers clearer, but not that of the people who live downstream, finds Smriti Mallapaty.
Satellite observations are providing a clearer picture of changes in the glaciers on the world's tallest mountain range — but there's still not enough information to answer a vital question: how will the changes affect the lives of about 1.3 billion people in Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan?
Running 2,000 kilometres from east to west, the Hindu Kush-Karakoram-Himalaya (HKKH) region contains an estimated 60,000 square kilometres of glacier and surface ice, often called the 'Third Pole'.
Himalayan glaciers have been the focus of fierce international debate since 2009 when it emerged that the 2007 report by the UN Intergovernmental Panel on Climate Change (IPCC) — the reports of which form the basis of international negotiations on slowing and tackling human-induced climate change — had erroneously stated that the glaciers could disappear by 2035 as a result of global warming.
The IPCC report described the region as a data 'white spot'.
This lack of information on whether Himalayan snow and ice is retreating or expanding is important, Andreas Kääb, a professor in the department of geosciences at the University of Oslo in Norway, told SciDev.Net.
This is because of the effect of global climate on losses or gains of glacier ice, and because many people living downstream depend on glacier-fed rivers for their water supply.
The basic problem, says Kääb, is the difficulty of doing research in such inhospitable terrain.
An extensive April 2012 review of Himalayan glacier research by an international team including experts from India and Nepal, published in Science, identified reasons for these data gaps. 
These include insufficient on-site measurements, few high-elevation weather stations, rugged terrain and remote location of glaciers, and sensitive political situations that make both access and international collaboration difficult.
But since 2011 satellite observations have begun to change the picture.
'The distance between the Himalayas and other mountain ranges [in terms of access to knowledge from satellite measurements] has become much smaller,' says Kääb.
Graham Cogley, professor of physical geography at Canada's Trent University, agrees. 'The Himalayas are now better measured thanks to studies from space,' he tells SciDev.Net.
But he also points to the continuing need for information.
If you are concerned with 'downstream water resources or downstream hazards, then you need as much activity in the field on the glacier as you can possibly afford', he says.
Studies from the skies
In 2011 the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD) published inventories calculating the entire glaciated and snow-covered area of the HKKH, based on satellite remote sensing imagery. 
This was followed by two studies this year calculating glacial mass changes for the entire mountain chain. One study by US researchers was published in Nature in February 2012, and the other, by Kääb and colleagues in France and Norway, was published in the same journal in August. [3,4]
They are regarded as important developments for understanding overall trends in the region.
The US team measured the Earth's gravitational pull to detect changes in mass on the Earth's surface.
The France–Norway team analysed laser signals sent by the Ice, Cloud and Land Elevation Satellite (ICESat) to the Earth's surface between 2003 and 2008. It used a laser altimetry technique that measures the time required for signals to beam back to the satellite, and converts this time into distance. The distance 'gets larger if glaciers shrink, or smaller if glaciers get thicker,' explains Kääb.
The analysis found an overall annual loss of 12.8 gigatonnes of glacier ice from the HKKH, three times more than the estimates gained from measuring the Earth's gravitational pull, but less than the mass changes calculated by conventional mathematical methods using scarce field data.
Kääb's team also reported 'pronounced regional variations', with Jammu and Kashmir thinning at the fastest rate of 0.6 metres per year, and the Karakoram, further west, thinning by only a few centimetres per year, or almost not at all.
The findings were in general agreement with a paper published in Nature Geoscience in April 2012, which reported that satellite remote sensing had confirmed slight gains in the mass of ice in the Karakoram. 
This is not necessarily surprising, given that the Himalayas vary greatly in topography, rainfall and snow accumulation, with the eastern glaciers accumulating the most during summer from the Indian monsoon, and the western glaciers accumulating the most during winter through westerly winds.
In September, a US National Research Council report said glaciers in the eastern and central Himalayas appear to be retreating at accelerating rates, while those in the western Himalayas are more stable and could be growing. 
Laying the groundwork
While scientists continue to study the findings, there is broad agreement that, aside from the Karakoram enigma, the region's glaciers are losing mass. But the melt seems to be occurring more slowly than previously feared: the glaciers of the HKKH are expected be around for the next couple of hundred, if not thousand, years.
But science in the region is still lacking in its understanding of 'the likely consequence of glacial melt on the region's local water supply', suggests the US National Research Council report. To establish the consequences, Cogley insists, requires not just satellite data analysis, but assessment on the ground — of which there is little.
Revealing the scale of the problem, Cogley says that just 20 of the 54,000 glaciers in the HKKH have been measured on the ground for 'mass balance', or net gains against net losses, with even fewer measured annually.
'In the Alps or Scandinavia we have some glaciers whose measurements go back 50 to 60 years, but there is nothing like that in the Himalayas. I believe the longest record is about 10–11 years,' he says.
Samjwal Bajracharya, a remote sensing specialist at ICIMOD, says the contribution of glacial melt to river run-off and how it will change over time must be pinned down. This information is crucial for planning community, urban, industrial and hydropower development in downstream areas, he says.
Kääb and his team calculated that glacial melt contributed two per cent to the waters of the Ganges, 3.5 per cent to the Indus and up to ten per cent in the Upper Indus. But he admitted that his team did not take a closer look at the impact of their results — 'what it means for the people, for water resources, for natural hazards to glacial lakes'.
The main natural hazards are the floods that occur when a dam holding glacial meltwater is breached, resulting in high-altitude flash floods.
The US National Research Council report suggests that other factors such as groundwater depletion, increased water consumption and varying patterns of rain and snowfall may have more of an impact on water availability in the coming decades than glacial retreat. But to establish this will, as scientists inevitably say, need much more investigation.
And that means more funding.
Eklabya Sharma, director of programme operations at ICIMOD, is optimistic. He says that countries in the region and international donors have shown increased interest in further research.
He says more funding is now being invested in capacity building in China, India, Nepal and Pakistan. India established a Centre for Himalayan Glaciology in 2009, and Kathmandu University started a Master's degree in glaciology in 2011. Norway recently provided funding for a five-year programme that includes glacier monitoring, remote sensing, establishing mass balance in some sites, and capacity building.
'Overall, there has been a substantial increase in attention and resources by countries [in the region] as well as institutions like ICIMOD,' concludes Sharma.