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.