Climate-change realities could ruin water planning

Study: Humans upset delicate weather balance

Shaun McKinnon
The Arizona Republic
Feb. 1, 2008 12:00 AM
Human-caused climate change could undermine a century of building dams, canals and reservoirs across the West as warmer temperatures alter the way water flows through the dry country, scientists say.

Two separate studies, published in today's issue of Science magazine, describe weaknesses in an already fragile system of stretching limited water supplies, suggesting that what happened in Arizona this week, when warm rains filled reservoirs too early, could occur more frequently.

One study attempts to quantify for the first time the human contribution to climate change in the West. It offers evidence that man-made greenhouse gases from vehicles or power plants have caused up to 60 percent of the variations in snowpack, stream flow and higher temperatures over the past half-century.

The second study argues that climate change has rendered the past all but useless in managing water supplies. What look like cyclical droughts could turn into a new climate regime. Water-storage systems built based on historical weather and climate patterns will fail more often as conditions change, forcing water managers to adapt or face shortages.

"We have built all of our infrastructure to maximize the world as we know it," said Tim Barnett, a researcher at the Scripps Institution of Oceanography in San Diego and lead author of one of the studies.

"As long as the climate stays the same, then we've optimized the system," he said. "But it's not going to stay the same. Things that used to work aren't going to work."

Losing water
Both of the new studies start with the premise that climate change already has begun affecting water supplies in the West. Barnett's research finds the earliest evidence as far back as 50 years ago and attributes it increasingly to human activities that produce carbon dioxide and other greenhouse gases.

Barnett said the researchers hunted for natural variables that could have caused such dramatic changes, poring over weather observations and tree-ring records dating back centuries. They considered solar activity and volcanoes.

At every step, he said, "the answer was no; there was no natural explanation."

But there were consequences: smaller snowpacks, winter rain in the high country, rivers that run out of water too soon, and drier, hotter summers.

Those changes chip away at the carefully balanced system of watering the West, one that counts on storing water as snow during the colder months and stashing it in reservoirs during drier periods.

If that system is upset, if rain falls instead of snow and runoff arrives before it's needed, then the water is lost.

'Old rules don't apply'
Although scientists are quick to say they can't attribute specific events to global warming, the warm storm that soaked Arizona provided an example of how an off-kilter climate could affect water management.

Rain fell even in the high country, sending water gushing down the Verde River to reservoirs that couldn't contain it.

Salt River Project was forced to release the overflow into the dry Salt River, unable to store it for later use.

Snow would have remained in the mountains and melted at a more manageable rate.

"That's a harbinger of the future right there," said Brad Udall, director of the Western Water Assessment, a Colorado-based research organization.

"Reservoirs actually need to get drawn down to get ready for spring runoff and for any additional rain," he said. "Because rain intensity is expected to increase with warmer temperatures, we're probably going to have to draw reservoirs down lower in the spring. In some years, we could wind up with less water stored."

Climate change also makes the past a less reliable tool to predict the future, Udall said, echoing the second study set for publication today.

"The old rules don't apply anymore," he said. "The real problem is we don't know what we're going to replace them with."

Drought and the future
In the Science magazine article, researchers say that human-caused changes in the climate will play havoc on the averages and extremes used to plan for floods, droughts and water storage. Those measurements help determine how much water needs to be stored or how cities allocate resources.

"Climate change magnifies the possibility that the future will bring droughts or floods you never saw in your old measurements," said Christopher Milly, the study's lead author and a research hydrologist for the U.S. Geological Survey.

"For agencies like the Army Corps of Engineers and the Bureau of Reclamation, this would mean fundamental changes in the way they do business," Milly said.

Scientists can't offer a solution yet, beyond urging water managers to consider a wider range of possibilities as they plan for the future.

"We need to have enough flexibility to change course in case the system goes in a way it hasn't before," said Kelly Redmond, deputy director of the Western Regional Climate Center in Reno, one of six climate-study centers overseen by the National Oceanic and Atmospheric Administration.

"We have to plan for possibly being in a new regime," Redmond said.

Whether the current drought represents a new regime is still unknown, Redmond said, but that question looms large in front of researchers.

"We know from the tree-ring records that the Southwest does experience long droughts on its own," he said. "Is it one of those droughts, or is it a new type of drought? That's what we don't know."

Looking for options
Water managers have long planned for droughts, which are expected occurrences in the desert. Global warming adds a wrinkle not everyone knows how to handle yet.

"All you can do is be prepared to look over a wider range of options," said Larry Dozier, deputy general manager of the Central Arizona Project, which delivers Colorado River water to Phoenix and Tucson.

Those options could include desalting brackish water or ocean water, working with farmers to change crop patterns or, if dry conditions persist, buying water from farmers to supply cities.

Arizona also fought hard during negotiations with the other Colorado River states to delineate specific guidelines for declaring shortages, hoping some advance knowledge would help avert disaster.

But if the old rules don't apply, the new rules may not work, either.

"There are no knowns right now," Dozier said. "We have no more certainty."