Saturday, February 2, 2008

Drought in the Southwest - "There are no knowns right now"

My wife, visiting family in Scottsdale, Arizona, called me this morning to tell me about a front page article in the Arizona Republic titled Climate-change realities could ruin water planning. The article was inspired by a new study reported in Science magazine - Stationarity Is Dead: Whither Water Management?

The killer quote (I thought) that wraps the AZ Repub article was this one, by Larry Dozier, deputy general manager of the Central Arizona Project, which delivers Colorado River water to Phoenix and Tucson:

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

Adaptation will be more an exercise of living with uncertainty that one of changing the way we live for a new steady-state environment. It won't be like traveling to another country and bringing the right clothes to fit a different climate. It will be more like being taken without any control to one new location after another, with surprise weather greeting you in each destination. You'd better bring everything from your swimming trunks to your down parka.

The article does a good job of explaining why the warm and heavy rains that have fallen on Arizona so far this winter are not the answer to its water shortage problems. The entire strategy of water management in the largely desert region of the American Southwest is based on snowpack. The real water storage should be held in the form of snow in the mountains of Arizona, Colorado and Utah, then released gradually to replenish reservoirs during the dry and hot summer months. If the winter precipitation falls as rain, it rapidly fills reservoirs to capacity, forcing releases of overflow into river channels - effectively wasting water that would have been available later in the year had it been in frozen state.

Authors of the Science article were interviewed for the newspaper article.

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."

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