FACTBOX: Impacts of glacier retreat on hydropower

(Reuters) - Retreating glaciers from the Alps to the Andes are likely to disrupt hydropower generation in coming decades.

Following are details of glaciers and the wider impacts of climate change on hydropower, the most widely used form of renewable energy:

* WORLDWIDE

More than a billion people live in river basins fed by glacier or snow-melt. Climate change will lead to a retreat of glaciers and cause wider disruptions to rain and snowfall patterns from tropical Monsoons to Arctic snowfall.

* ASIA

Himalayan glaciers may shrink to 100,000 square km (40,000 sq miles) by the 2030s from 500,000 sq km if current warming rates continue. That would increase river flows in some river systems for two to three decades, followed by decreasing flows.

Water supplies will be hit in areas fed by melt water from the Hindu Kush and Himalayas, on which hundreds of millions of people in China, Pakistan and India depend.

* EUROPE

Small glaciers will disappear and larger glaciers will shrink by between 30 and 70 percent by 2050.

For the whole of Europe -- where 20 percent of electricity comes from hydropower -- generating potential of hydropower plants is projected to decrease by six percent by the 2070s, mainly because of changes in precipitation.

That translates into a 20-50 percent decline around the Mediterranean, a 15-30 percent increase in northern and eastern Europe and little change for western and central Europe.

* SOUTH AMERICA

Over the next 15 years, inter-tropical glaciers are very likely to disappear in the Andes, reducing water availability and hydropower generation in Bolivia, Peru, Colombia and Ecuador. The issue is already "critical" in the four nations.

* NORTH AMERICA

A potential fall in the level of the Great Lakes could mean big economic losses as a result of reduced hydropower generation both at Niagara and on the St. Lawrence River.

By the 2020s, about 41 percent of water supplies to southern California are likely to be vulnerable to warming from loss of Sierra Nevada and Colorado River basin snowpack.

* AFRICA

Hydropower generation is likely to be hit by climate change, according to a study of hydro-electric power generation in the Zambezi Basin. The snows on the peak of Kilimanjaro, Africa's highest peak, have shrunk by 80 percent in the past century.

* AUSTRALIA, NEW ZEALAND

Annual streamflow in Australia's Murray Darling basin is likely to fall by 10-25 percent by 2050 and 16-48 percent by 2100. In New Zealand, annual flow from larger rivers in the Southern Alps is likely to increase. Proportionately more runoff is very likely in winter and less in summer -- helping hydro-electric generation during the winter peak demand period.

(Sources: 2008 and 2007 reports by the U.N.'s Intergovernmental Panel on Climate Change - IPCC)

(Reporting by Alister Doyle; editing by Sara Ledwith)