ICA, Peru - Two decades ago, the strip of sand between the Pacific Ocean and the Andean foothills was empty except for the occasional fig or carob tree. But the northern end of perhaps the world's driest desert – a harsh and unforgiving clime – is now the center of Peru's export agriculture industry.

Rising demand for irrigation and drinking water is draining the aquifer faster than it can recharge, and a scheme to channel more water from the Andean highlands, which receive seasonal rainfall, is pitting big agribusinesses on the coast against Quechua-speaking llama herders in the mountains.

Experts say the conflict is just one sign of rising tensions over water use as supplies of the vital resource dwindle and shift with changes in climate.

"Water belongs to the people who need it most, and we need it most," says Gino Gotuzzo, of the Farmers Association of Ica, who grows asparagus and some other crops on about 60 acres of desert. Up the mountain, however, Quechua-speaking farmers say plans to channel runoff to coastal farms will dry up the spongy high-mountain wetlands where they pasture llamas and alpacas, ruining their livelihood.

Peruvian officials brush aside the specter of "water refugees." As supplies dwindle, they say, they can channel water from the highlands, where rain falls between October and April, or divert rivers that flow east to Amazonia, which receives more precipitation than its sparse population uses.

Nevertheless, droughts associated with El Niño events in the 1980s and 1990s spurred increased migration from rural areas to cities in Peru, and the exodus from Brazil's chronically drought-stricken northeast is one factor in that country's Amazonian deforestation.

With cities growing and agriculture expanding throughout South America, experts predict that climate change will exacerbate water scarcity, increasing conflicts between competing users, pitting city dwellers against rural residents, people in dry lands against those in areas with abundant rainfall, Andean mining companies against neighboring farm communities, and eucalyptus plantation operators on the Argentinean and Uruguayan plains against farmers who say the trees are sucking the water table dry.

In Peru, officials say the problem is not water scarcity, but Nature's poor distribution. More than two-thirds of the country's 29 million people live on the dry western side of the Andes, where less than 2 percent of the country's water flows, while only one-fourth live in Amazonia, which can get more than 80 inches of rain a year.

But plans to redistribute water by rerouting rivers or drilling through the Andes raise questions for which neither politicians nor scientists have easy answers. How much water can be piped from reservoirs in the Andean highlands or Amazonian cloud forest without damaging those ecosystems? Who has priority: thirsty cities or food producers? Subsistence farmers or export agribusinesses? Poor rural communities or revenue-generating mines? Agriculture or hydroelectricity?

On Peru's coast, virtually every city has its eye on an uphill neighbor's water supply. In neighboring Bolivia, street protests in 2000 and 2004 known as the "water wars" forced two private companies, Bechtel and Suez, to give up water management concessions. City planners in Quito, Ecuador's capital, are looking to the Amazon to replace water supplied by dwindling glaciers. And Brazil plans to meet its growing energy needs by damming rivers throughout the Amazon, which critics say could further disrupt the region's hydrology.

The Intergovernmental Panel on Climate Change predicts that by 2020 upwards of 1.5 billion people worldwide will be facing water stress, including anywhere from 7 million to 77 million in Latin America.

"Inherent in these projections," said IPCC Chairman Rajendra Pachauri, "is the potential for conflicts and the disruption of peace."

With nearly 9 million people, Lima, Peru's capital, is the second-largest desert city in the world, after Cairo. It grew up beside a river that slices down from the Andean highlands to the Pacific Ocean. Many such coastal valleys contain vestiges of pre-Hispanic canals and irrigation systems, a sign that water management has been a challenge for several millennia.

"Lima is a thirsty city," says Guillermo León, president of the board of directors of the state-run water and sanitation company, SEDAPAL. In shantytowns lacking water hookups, residents must buy water from tank trucks. They use less than one-third the amount of water used by residents of wealthier districts, but pay four or five times as much for the water.

Water stress is also serious on the Bolivian Altiplano, the two-mile-high plain near Lake Titicaca, an area that is home to more than 3 million people. That region's rivers provide an average of 132,000 gallons of water per person per year – scarcely enough for household use, even if Bolivians are thriftier than US families, who can use up to 400 gallons a day, according to the U.S. Environmental Protection Agency.

Often, the scant water available is polluted. Three-quarters of wastewater in Peru is dumped untreated into rivers, lakes and the Pacific Ocean, and the Health Ministry has identified dozens of rivers polluted with lead, cadmium, arsenic, mercury and other metals from mining operations.

In the Andes, these problems are exacerbated by demand for water for irrigation. About 80 percent of Peru's water goes to agriculture, and only 8 percent of farm land uses water-conserving systems like drip irrigation, according to Abelardo de la Torre, head of the new National Water Authority, which is overseeing the design of watershed management plans throughout the country.

The need for efficient irrigation will become critical within the next few decades, as ice caps disappear from the Andes, where most of the world's tropical glaciers are located, and where small farmers depend on meltwater during the dry season.

Outside La Paz, Bolivia, the Chacaltaya glacier, once billed as the world's highest ski resort, is nearly gone. And Ecuador plans to pipe water from the eastern side of the Andes to supplement the dwindling supply from two receding glaciers that provide Quito's drinking water.

In 1991, tropical Andean glaciers covered some 1,065 square miles, with 70 percent in Peru, 20 percent in Bolivia, and the rest in Ecuador, Colombia and Venezuela. Since then, glaciers have disappeared from Venezuela and are shrinking in the other countries. Calculations show a loss of nearly 10 percent per decade.

Ironically, the increased melting means a water bonanza now, but César Portocarrero, an engineer who helps small farmers install drip irrigation systems in Peru's Cordillera Blanca, named for its snow-capped peaks, said he has seen an increase in conflicts between neighbors and communities, which may be an early sign of water stress.

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.