It is not clear how much the loss of glacial runoff will affect drinking water supplies downstream. Experts say much of the decrease can be offset by expanding reservoirs to catch water during the rainy season.
But potable water will not be the only casualty. A World Bank study indicates that glacial melt it is likely to raise generating costs at hydroelectric dams on rivers fed by melt water.
Nevertheless, a hydroelectricity revival is underway in South America, especially in water-rich Amazonia. Not only will that add to the competition for water, but environmentalists also worry that dams like the controversial project on the Madeira River in western Brazil will block the flow of nutrient-bearing sediments and fish migration routes.
Dams may also change the hydrological cycle in Amazonia, which affects precipitation in the Andes. Climate models and scientists do not agree on exactly what changes will occur in Amazonia. Some will depend on whether El Niño cycles are more frequent or intense. Researchers are handicapped by a lack of historical data from Amazonian countries.
"We know more now than we did 20 years ago, but we still don't know half of what we need to know," said José Marengo of Brazil's National Institute of Space Research in Sao Paulo. "There are few studies and little meteorological data. There are huge data gaps in all the countries. In hydrological data, there are series of 20 or 30 years, when we would need 100 years or more to see if there is a cycle of flooding and drought."
Small farmers in the Andes, however, say there is already sufficient cause for alarm. Concerns over water shortages and salinization of pasture and crop land have spurred protests against large mines in Piura, in northern Peru, and near Oruro, in southern Bolivia, by farmers who say there is not enough water to go around.
Meanwhile, the tension continues between export agribusinesses on Peru's southern coast and the small farmers upstream. Large-scale farmers on the coast have more efficient irrigation systems, but the profusion of wells is pumping water out of the aquifer nearly twice as fast as it can recharge, according to Javier Chiong of the Ministry of Agriculture in Ica.
Large farmers downstream are calling for a major infrastructure project to channel water from the highlands, dispersing some of it through canals in the desert to recharge the aquifer. Small farmers and llama herders upstream say the scheme could dry the Andean bogs, an ecosystem about which little hydrological data exist.
"There's a lack of planning," said Gotuzzo of the Farmers Association of Ica. "And it's the poor people who will suffer the most. The rich will be able to solve their problems."
This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.