Highest-elevation glaciers keep their cool
A case study from the Nepal Himalaya shows no melt over large areas, and relatively small contribution to streamflow
The most striking feature of Asia's Himalaya Mountains — their breathtaking height — makes Himalayan glaciers far less vulnerable to melting than their lower-elevation counterparts.
It's cold at 18,000 feet and above. Really cold. All the time.
That may seem perfectly obvious, said CIRES Fellow Richard Armstrong, but the basic facts appear to have eluded many people.
"We have all heard these stories about how Himalayan glaciers are melting faster than anywhere else, drinking water is disappearing, there will be widespread catastrophic floods, etc. . . ." said Armstrong, a glaciologist at CIRES National Snow and Ice Data Center. "Well, when you start looking, there's really no data to support those statements."
A couple of years ago, when a colleague of his was approached by the World Bank, Armstrong agreed to help search for data from Himalayan glaciers, to assess the veracity of water resource fears.
"The World Bank is approached by people wanting to borrow money to build dams, and they wanted to know if there's going to be any water left to fill them." Armstrong said.
So Armstrong and his colleagues set about trying to estimate, for a remote and difficult-to-access region, how much streamflow came from glacial melt as opposed to
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Himalayan glaciers resist melt across 50 percent of their surface, and contribute much less to streamflow than assumed.
monsoon rains and the melt of the seasonal snow cover.
"We thought this work would be a literature search," Armstrong said.
"But we couldn't find any real research in this area."
What his team did find in the literature were plenty of big numbers. Glacier termini were retreating 10 to 60 m a year. There were estimates that glacial melt provides 50, 60, 70 percent of the flow of the Ganges.
It sounded quite dire, but the researchers knew first that termini measurements are not the last wordon glacial melt, especially at the higher elevations. Termini can retreat even when glaciers are gaining mass overall, through snowfall at higher elevations. Moreover, the streamflow estimates had no robust calculations to support them.
So the team began looking for raw data. Little or no data were available across much of the Himalaya, but the team identified nine basins in Nepal that contained digital glacier maps, stream gauge data, and the availability of NASA's Shuttle Radar Topography Mission — so high-quality digital elevation data were available.
"We got everything we needed, thanks to the collaboration and cooperation of various institutions in Nepal," Armstrong said.
After developing a method to estimate the current mass balance on the Nepalese glaciers, one that took into consideration their high elevations, the team reached two key conclusions:
- Glacial melt contributes from 2 to 20 percent of the streamflow in the basins studied, much lower than anecdotally estimated, and
- More than 50 percent of the surface area of the Nepalese glaciers never melts at all, during any time of year.
Globally, the prognosis for glaciers is dismal, said Armstrong. He spent years studying glaciers in the mountains of Washington State, where many glaciers are currently retreating and melting rapidly. There's little doubt that glaciers in many locations across North America and the European Alps are melting, and that the same is true throughout the world at elevations below 14,000 feet.
But the glaciers of the Himalaya at elevations of 18,000 feet and above are holding their own quite well, Armstrong said. "It's a bit simple, but the situation changes when you go up, when you're at elevations that the rest of the world doesn't see."
