Water, climate change: recipe for trouble?

As the Navy likes to remind us, water covers 70 percent of our planet and enables global commerce. Military strategists also caution that future wars will be fought over access to waterways and even over drinking-water supplies. And yet, we still lack a comprehensive understanding of how the world's water possibly could be affected by the phenomenon of climate change.

Many parts of the world are experiencing shifts in temperature and precipitation, which in turn affect wildlife and natural resources. As a result, scientists internationally are sounding a collective call to study how the changing climate is influencing that cycle and, in particular, how water behaves in the ecosystem.

To begin investigating the dispersal of water from mountaintops, through landscapes and into rivers and oceans, researchers at the University of Arizona are planning to conduct long-term experiments at a glass-enclosed facility in the southwestern desert. Once dubbed a failed science experiment for space colonization, the Biosphere 2 is being renovated this summer to accommodate the ecohydrology research,

"Our goal is to make a predictive tool for how water behaves in our environment," says Travis Huxman, director of Biosphere 2 and an associate professor of ecology and evolutionary biology at the University of Arizona, which took over management of the 3.14-acre facility last July.

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Scientists currently use statistical models to make predictions, such as how rainfall will influence river behavior, "But the reality is, you can't extend those statistical tools into an uncertain future," he says,

The elements of global climate change--rising temperatures and changes in carbon dioxide concentrations, precipitation and nitrogen deposition--all affect water behavior within an ecosystem. For exam pie, when there is a higher concentration of carbon dioxide in the atmosphere, plants tend to absorb more water.

But because it is difficult to predict how ecosystems will respond to all those varying elements at the same time, the scientists are constructing specific landscapes to help them isolate the different factors.

Inside the intensive agriculture biome of the Biosphere 2, scientists are building three "hillslopes" in separate bays that measure 30 meters long and 18 meters wide. These hillslopes consist of specially shaped basins, called zero-order catchments, which slope at a 12-degree angle and converge in a gully. When filled with soil, the landscapes will allow researchers to examine the ecology, hydrology and geochemistry that occur in the sedimentation. Ecologists and hydrologists will learn how water flows and how alterations to the spatial distribution of soil moisture affects what plants grow and where they grow, says Huxman.

Scientists will force a seasonal climate upon the landscapes, which initially will remain barren for 200 to 500 days. During that time, scientists can measure how water moves naturally through the soil. Then they will add plants and other vegetation to examine how water filters through those life systems.

"The idea here is that that will accelerate our understanding of global change," he says.

The unique ability of the Biosphere 2 to seal out the Earth's atmosphere on demand will help scientists monitor the exact composition of air that flows in and out of the experiment.

"To do this in the real world would be impossible," Huxman says. Scientists not only would have to control the weather, the soil evolution and the species composition in the ecosystem, but they also would require the ability to measure the water flow wherever it might travel.

The enclosed facility gives scientists that control.

"The Biosphere 2 is really the first attempt by people in the ecological and environmental sciences to ask a really big question, so even doing science at that scale is really new to this discipline," says Huxman.

Though the landscapes are not exact replicas of a hillslope and its associated ecosystem, they are downscaled tools that will allow scientists to investigate the mechanisms of water flow and extrapolate their theories to the real world.

Huxman says that those theories will yield better methods for predicting water flow in the future. "If atmospheric scientists can tell us how the distribution of precipitation will be in the future, then we can more accurately say how much of that water makes it down a river to the human endeavor," he says. "Right now, we don't do a good job of that."

The program has received funding through gifts and grants to run the experiment for l0 years on an annual $5 million budget. Scientists hope to continue well beyond that time frame.

The research ultimately could be useful for military planners as they try to figure out how climate change issues might be of concern to global security.

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