| RHONE GLACIER, Switzerland
RHONE GLACIER, Switzerland Standing on the glacier at the source of the Rhone river, glaciologist Andreas Bauder poses next to a 3-meter high pole sticking out of the ice, and gestures above his head.
"This is about the melt of one month," he says, as fellow scientists drill into the ice. "I'm about two meters tall."
From the Himalayas to the Andes, faster-melting glaciers spell short-term opportunities -- and long-term risks -- for hydroelectric power and the engineering and construction industries it drives.
The most widely used form of renewable energy globally, hydro meets more than half Switzerland's energy needs. As summers dry and glaciers that help drive turbines with meltwater recede, that share may eventually fall.
A study by Lausanne's EPFL technical university forecast a decline to 46 percent by 2035 for hydro from around 60 percent now as precipitation declines and total energy use increases.
In the same way as the Himalayas are "Asia's water-tower," Switzerland is the source of Europe's biggest rivers, supporting agriculture and waterways, and cooling nuclear power stations.
Water trickles down white-blue crevasses and ice cracks and creaks as Bauder, who for Zurich technical university spends about 20 to 30 days a year working on Swiss glaciers, explains that most of the mighty Rhone glacier will be gone by the end of the century.
"Nature can adjust to the circumstances," he said. "It's just people who are much more fragile about living conditions."
More than a billion people worldwide live in river basins fed by glacier or snowmelt.
Glaciers have been retreating dramatically since the end of the Little Ice Age in the 19th century, particularly in the Himalayas where they feed rivers including the Mekong and Yangtze and ensure water and power for fast-growing economies.
A lack of water for hydropower is already "critical" in Bolivia, Peru, Colombia and Ecuador, according to the U.N.'s Intergovernmental Panel on Climate Change, which also sees risks to water supplies to southern California from the loss of the Sierra Nevada and Colorado River basin snowpack.
In Europe, 20 percent of electricity comes from hydro -- generating potential that is projected to decrease by the 2070s, falling sharpest in the Mediterranean.
Bauder pointed to an area of stony ground and small lakes beyond the end of Rhone glacier ice field: "When I was a kid, I remember that the glacier was much larger. The glacier tongue was still reaching over this rocky area."
WINNERS AND LOSERS
The Swiss hydroelectric industry is part-funding Bauder's research, to help it take a long view on new projects in an industry where licenses often run for up to a century.
Other risks researchers have identified include sudden floods from swollen glacial lakes. Demand for more pumping technology and dams is one response in countries which can afford them.
Experts stress that forecasts so far ahead are highly uncertain, particularly in predicting precipitation, and note that some regions may even benefit.
"With climate change there will be some areas in the world with more precipitation year round," said Petra Doell, a professor of hydrology at the University of Frankfurt and a member of the U.N. climate panel.
"That will mean more hydropower generation even if glaciers melt."
For example Norway, which generates almost 100 percent of its power from hydroelectricity, is likely to get more rain and snow because of climate change even as glaciers retreat.
But if glaciers do disappear, one main impact will be lower river flows in dry seasons -- when irrigation is often needed for crops. That would particularly threaten people in the world's biggest rice-growers, China and India.
Nations with high power demand in dry seasons could suffer from lower flows, but Doell said hydropower reservoirs could be used to mute the overall impacts of melting glaciers downstream.
"A reservoir helps to broaden the availability of water throughout the year," she said. "But there are few dams in south-east Asia, where the impacts of melting glaciers will be most severe."
WAYS TO STORE WATER
From the Swiss perspective, the Lausanne study forecasts run-off from the Swiss Alps will fall by 7 percent to 2049, as glaciers recede and precipitation rises by 6 percent in winter and drops by 8 percent in summer.
These wetter winters and drier summers may force changes in the way Switzerland stores and moves water.
In the past, the country used to make sure its storage lakes were full in September to provide hydropower for heating as energy demand peaked in winter, while they were empty in April, ready to be replenished by melting snow and ice.
"Since the electricity market was liberalized and listed companies involved, which are more oriented to earning money and delivering energy at the best price, it has been more difficult to fill the lakes in the winter," said Bruno Schaedler, a hydrologist from Bern University.
The melting glaciers will be a bonus in the short term, but the hydro industry will have to manage water more efficiently: "When we don't have the reserves of the glaciers, we will need more storage dams," said Joerg Aeberhard, head of hydraulic production at Swiss energy company Alpiq.
Swiss hydropower is not completely dependent on glaciers, he stressed: melting snow is more important and provides run-off with less sediment. "We are worried about climate change, but I am more worried as a citizen than as a generator of hydroelectric power."
By the end of the century, the Lausanne study forecasts run-off will have fallen by 17 percent as the glaciers will have virtually disappeared.
About 55 percent of the 100 cubic km of water stored in Switzerland's glaciers at the end of the last mini Ice Age in 1850 was gone by 2006. Total water stored in the glaciers of the European Alps as a whole had fallen two-thirds to 61 cubic km in 2006.
Bern University hydrologist Schaedler said Switzerland would probably need to make more use of pumped storage power stations -- which pump water into high reservoirs when demand is low, to release the water as demand peaks -- to manage changing flows in run-off and help the rest of Europe cope with more unpredictable precipitation.
While winters may be wetter and summers drier, he said the fact that the Alps attract three times heavier rainfall than the average for the rest of Europe suggests the country will still be relatively comfortable.
"The role of Switzerland as a water tower will become more important for the rest of Europe with climate change and changing precipitation," Schaedler said.
(Additional reporting by Alister Doyle in Oslo; Editing by Sara Ledwith)