Adán Pajuelo is harvesting carnations, deftly clipping stems as he hustles down the row, when he pauses to glance up the mountain toward the source of water for his field—a lake and the glacier that feeds it. His community is concerned about a local utility’s use of water from the lake, and about possible downstream pollution from a mining project planned nearby.

“The retreat of the glaciers is a huge concern for everyone. It makes us think that we won’t have water in the future,” says Pajuelo, who heads the local organization of water users in this Andean farming community. He says he fears the mine “will take away what water we have.”

The glaciers in Peru’s central Cordillera Blanca are shrinking steadily, leaving policymakers and water users along the Santa River to grapple with long-term implications that may include not just less water during the dry season, but also a greater concentration of pollutants as a consequence of lower water flow. And recent studies show that the dry-season water flow may be decreasing faster than previously believed, giving people less time to adapt.

“The major problem is that there are no government policies” for addressing the problems stemming from shrinking glaciers, says Fidel Broncano, mayor of Caraz, a town of about 30,000 people on the Santa River, downhill from Pajuelo’s field.

This state of affairs, however, is beginning to change. A new US$1 million project financed by the Inter-American Development Bank focuses on climate-related disaster risk management in seven regions. These include the Callejón de Huaylas, a valley at the foot of the Cordillera Blanca where the Santa River flows toward the Pacific Ocean, 347 kilometers (216 miles) away.

And in late February, it was announced that the state-run National Water Authority and various government ministries—including Environment, Agriculture, Energy and Mines, Housing, Health and Production—will sign an inter-agency agreement to share data and research results, coordinate water policies and implement the country’s National Water Plan.

Nearly all of the glaciers in the tropics—the belt around the Earth between 30 degrees north and 30 degrees south latitude—are in the Andes Mountains. Peru has about 71%, Bolivia 20% and Ecuador 4%, with the remainder divided between Venezuela and Colombia. But the Andes’ ice cover has been shrinking for over half a century. The rate was relatively slow in the 1960s and 1970s, began quickening in the late 1980s and has risen sharply in the past decade. On average, Andean glaciers are now retreating at the rate of about 2.5% annually, according to French glaciologist Antoine Rabatel.

Since the 1960s, the glaciated area in Peru, Bolivia and Ecuador has generally shrunk by between 20% and 35%, although the glacier on Ecuador’s Mt. Chimborazo has lost more than half its area since the 1960s. Venezuela’s total glaciated area decreased from 2.03 square kilometers (0.78 sq miles) in 1952 to just 0.3 square kilometers (0.1 sq miles) in 2003.

Because precipitation has remained fairly steady during those years, the shrinkage is due not to reduced snowfall but to rising temperatures, Rabatel says. He expects most of the lower peaks in central Peru’s Cordillera Blanca to be ice-free by the middle of this century, although peaks taller than 5,400 meters (17,716 feet)—including the iconic Mount Huascarán, at 6,768 meters (22,204 feet)—are likely to remain white. (See “As glaciers melt, so does climate record”—EcoAméricas, Sept. ’07).

With its postcard-perfect snowcapped peaks, the Cordillera Blanca is Peru’s best-known and most studied glaciated mountain range. Facing it across the river are the ice-free hills of the Cordillera Negra. During the rainy season, from October to April or May, farmers on both sides rely on rainfall for their crops.

During the rest of the year, however, farmers in the Cordillera Blanca have an edge, because the glaciers serve as a reservoir, storing precipitation as ice and gradually releasing it during the dry season. Hydrogeologist Jeffrey McKenzie of McGill University in Montreal, Canada, says glaciers are “hydrological Prozac; they smooth out the highs and lows.”

McKenzie, an associate professor of earth and planetary sciences, is one of a group of Canadian and U.S. scientists studying glacial melt and its impact on downstream water users as part of a US$1 million project funded by the U.S. National Science Foundation.

The group, which includes glaciologists, hydrogeologists, geographers, biogeographers, anthropologists and a historian, is tracking water from glaciers in the Santa catchment to determine how much runs off as surface water, how much filters into groundwater and how long water stays in the ground before it reaches the Santa River. They hope their data will help government officials design and implement water-management policies for the watershed.

Glaciers contribute relatively little to the Santa during the rainy season, when most of the river’s flow comes from precipitation. In the dry season, however, they account for about 30%.

So while fears of a waterless future are unfounded, dwindling water flows from glaciers could have important consequences in the Santa River Valley. Water supplies there already are being stretched, thanks to the demands of farmers and towns, a hydroelectric plant and two export-agriculture irrigation projects far downstream on the desert coast, says hydrologist Michel Baraër, an assistant professor at the University of Quebec.

Water-management planning is particularly urgent because the Santa appears already to have passed a point Baraër calls “peak water.” When glaciers begin to melt, they release a sudden surge of water, he says. Over time, however, that amount drops until the melt water flow stabilizes again at a lower level.

Measurements from six glacier-fed tributaries of the Santa River indicate that “peak water” probably passed in the 1980s, Baraër says. “Thirty percent less is a lot, and it is a reality now,” Baraër adds. “We don’t have 50 years to adapt. The question is, ‘How do we share the water [when] the resource is declining?’”

Some nonprofit organizations have helped farmers prepare by installing drip irrigation systems for their crops, which include corn, wheat, potatoes and flowers. Ironically, however, some experts say flooding poses a more immediate danger than drought.

That’s because warmer temperatures mean more precipitation falling as rain, rather than snow, on steep mountain hillsides. This tends to ncrease the risk of flash flooding and landslides. Blocks of ice may also tumble down from glaciers and crash into lakes, triggering outburst floods as water breaks through or washes over natural dams. (See “Falling ice from glacier gives Peru climate-change preview”—EcoAméricas, April ’10.)

Records of outburst floods and avalanches date back to colonial times. They show that in the Callejón de Huaylas portion of the Santa River Valley alone, such disasters have killed some 23,000 people since the 1940s, according to historian Mark Carey of the University of Oregon. But with the Callejón de Huaylas population on the rise, the stakes are now higher. If an outburst flood from Lake Palcacocha were to occur today on the scale of the one that happened in 1941 that flattened much of Huaraz and caused 5,000 deaths, Carey says, it might kill tens of thousands.

Further downstream, 4,000 people died in the town of Ranrahirca in 1962 in an avalanche that began on Mount Huascarán. Eight years later, an earthquake shook loose another mass of ice and mud from Huascarán that buried an estimated 15,000 people in neighboring Yungay, where only the top of the old church tower still pokes above the ground.

The National Water Authority’s Glaciology Unit monitors lakes, draining some water when they reach hazardous levels, says Jesús Gómez, coordinator of glaciology studies for the unit.

But towns in the valley have been slow to take disasters seriously, says Josefa Rojas, who coordinates the Inter-American Development Bank climate-change adaptation project for Peru’s Environment Ministry. Working in the Quilcay River watershed below Lake Palcacocha, where the government declared states of emergency in 2010 and 2011 because of flood risk, the project will measure and track the flow of water in order to model landslide hazards and develop risk-management plans.

Researchers will also study water quality, particularly acidity and heavy metals, Rojas says. She adds that the work in the Quilcay watershed will include phytoremediation—using plants to improve water quality.

Two investigators—McGill University’s McKenzie and Bryan Mark, an associate professor of Geography at Ohio State University—measured the pH of a stream in a neighboring valley and found that it registered about 3.4. That’s as acidic as orange juice, and considerably below the range of 5.5 to 9 that the U.S. Environmental Protection Agency recommends for drinking water.

Mark suspects the acidity is the result of a chain of events related to the changing climate. As glaciers retreat, he says, they expose more mineral-bearing rock. Once exposed to the air, those minerals oxidize, increasing the acidity of runoff flowing over the rock. Acidic water dissolves more heavy metals, sometimes to a degree that makes it unfit for human consumption or agriculture.

Those streams flow into the Santa River, where they mix with runoff from other watersheds in which old mine tailings are polluting the water with metals such as lead, cadmium and mercury. The Santa River is further contaminated by sewage and solid waste from towns along the banks that lack landfills and treatment plants.

“The first thing we have to do is restore our polluted rivers,” Gómez says. “They are the cities’ sewers.”

A decrease in the Santa’s flow is likely to increase the concentration of contaminants, says Mark, who is monitoring discharge rates and pollution at more than 20 points along the river, from above Huaraz to the coast. High levels of pollution, especially from heavy metals, could affect the large Chavimochic export-agriculture project on Peru’s desert coast.

Chavimochic diverts water from the Santa to irrigate some 75,000 hectares (185,000 acres) of desert, allowing cultivation of export crops including asparagus, artichokes and fruits. There are plans to expand the project to 144,000 hectares (356,000 acres), with a large reservoir to ensure a water supply during the dry season. Chinecas, another irrigation project slightly to the south, also draws some water from the Santa. Eventually, water from the Santa may no longer reach the Pacific Ocean in the dry season, Carey says.

As demand grows and the Santa’s flow decreases, some experts foresee tussles over water in the Callejón de Huaylas. One conflict erupted in 2008, when farmers in Pajuelo’s community blocked access to Lake Parón, a glacial lake above Cruz de Mayo, accusing Duke Energy, which operates a hydroelectric dam on the Santa, of overdrawing from the lake and destroying irrigation infrastructure with the heavy flow.

The farmers padlocked the dam’s sluice gates, launching a two-year standoff that only ended when government officials, worried that the lake’s water level had risen to a danger point, negotiated a solution.

Tensions remain, however, and are exacerbated by the farmers’ concerns about a gold mine planned for the area. Though the mine would not affect Lake Parón directly, Pajuelo and his neighbors worry it would foul irrigation water downstream. Concern about water supply and quality of water have led to several inconclusive meetings with authorities.

Discord over Lake Parón could be a sign of conflict to come, says Adam French, a researcher from the University of California-Santa Cruz, who has been studying water use in the Callejón de Huaylas.

As the population grows and glaciers continue to shrink, French says, “there will be increasing competition for the use of a resource that is not increasing in quantity.”