Peru's glacier meltdown threatens water supplies

As glacier meltwater trickles down mountainsides in the Andes, some places in Peru may already be seeing temporary increases in water supply, according to new research published in ES&T (DOI: 10.1021/es071099d). But as the ice disappears, researchers say, so will the water that flows from it, and people will be hit especially hard during the dry summers when glaciers normally release water. How severe will local shortfalls be, and how soon will they affect millions of people in South America?

In the city of La Paz (Bolivia) and its suburb El Alto, more than 2 million people get about a third of their drinking water from glaciers—and those glaciers have shrunk by more than half since the 1960s, according to Walter Vergara, a World Bank expert on climate change in Latin America. The situation in less monitored areas is more of a mystery. Satellite images show that glaciers are shrinking, but they don't provide a reliable estimate of how much water is released or where it goes, and climbing glaciers to get better measurements is risky and expensive.

To overcome these limitations, a team led by geographer Bryan Mark of Ohio State University developed a stable-isotope method that can determine how much of a community's water supply is glacier-fed, without scaling the glaciers. The technique relies on differences in the levels of naturally occurring isotopes of hydrogen and oxygen from glaciers compared with rainwater and other sources. Water samples collected from streams are analyzed for isotope levels by mass spectroscopy to determine the percentage of glacier-fed water they contain and that fraction can be monitored for changes over time.

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