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Study Warns of Less Colorado River Water

Posted on: Wednesday, 14 March 2007, 09:00 CDT

By TONY DAVIS, ARIZONA DAILY STAR

Global warming likely will mean less water for the already overallocated Colorado River in coming years, the nation's most influential research organization concluded Wednesday.

That means more severe droughts over the next century that will require better management and strong, sustained cooperation among the seven river basin states, the National Academy of Sciences says in the first study by a major research group to say that climate change is likely to shrink the river's supply.

Residents of Arizona and the other six states should prepare for "costly, controversial and unavoidable tradeoffs" in water use, the report says.

In Arizona, the report means the state needs to buy and store more surplus river water supplies that remain, and may need to limit growth in the distant future, a State Department of Water Resources spokesman said.

"The preponderance of scientific evidence suggests that warmer future temperatures will reduce future Colorado River streamflow and water supplies," the academy report says.

Some water shortages can be eased by conservation, technological improvements such as desalinization and buyout of farms. But the academy warns that technological change and conservation aren't panaceas for future water problems because "demand is inexorably rising" due to growth. Agriculture buyouts could reduce the region's ability to produce food, the report adds.

The report was written by a panel of a dozen scientists, including three from the University of Arizona and the U.S. Geological Survey in Tucson. It recommends no specific actions beyond a study of regional urban water practices.

While many water managers are aware of the report's conclusions, part of the general public doesn't recognize how precious regional water resources are, said one of the authors, UA associate geography professor Connie Woodhouse.

"You turn your tap on at home, water comes out," said Woodhouse, who worked on the report while a scientist for the National Oceanic and Atmospheric Administration in Boulder. "It's not a given. It's something we have to be aware of: potential scarcity and a finite resource."

In Arizona, the prospect of river flows slashed by global warming means the state should step up efforts to recharge water, said a water department spokesman and a former state water official. It already has artificially recharged 3 million acre-feet into three basins in the Phoenix and Tucson areas.

Transfers of water rights are possible to cities from farms, which use 60 percent to 70 percent of the state's water. One idea: paying farms in advance for the right to parts of their supplies in dry years, said Kathy Jacobs, director of UA's Arizona Water Institute.

In the long term, however, drought-reduced water supplies could lead to higher prices that could limit population growth, said Jack Lavelle, a Department of Water Resources spokesman.

Lavelle and Jacobs, a former director of the department's Tucson management area, said air quality, traffic and hotter temperatures are more likely to limit growth than water. Arizona is blessed with water compared to neighboring states and has gone much further in banking and storing Colorado River water, Lavelle said.

The state is also negotiating an agreement in which Nevada would pay Arizona to buy and store more water, in exchange for Nevada's being able to use water that it plans to import from northern Nevada and store in Lake Mead. Arizona would normally have the right to take some of that water under century-old legal agreements.

But if a drought-induced shortage extended over several years, "we may find ourselves in some kind of extreme conservation measures," Lavelle said. If rural developers can't find adequate water supplies in such a scenario, that will probably affect growth, he said.

In urban areas such as Tucson, if water is so expensive that developers can't make a good enough deal to ensure some profit, "that might be a limiter on urban growth," he said.

The academy report confirms what many scientists had warned about since the mid-1980s about warmer temperatures' threat to the river. The report points out that tree ring records dating back 500 years show that many severe, extended droughts have struck the region that are worse than the current drought.

Researchers are divided over whether global warming will mean more or less rain. But scientists generally agree that warmer temperatures mean less river runoff even if rainfall stabilizes. One reason: Warmer weather brings more rain and less snow, and rain is likely to be absorbed into the ground - not streaming into rivers.

A study by a National Oceanic and Atmospheric Administration researcher warned last year that the Colorado's flow could at times shrink by half under the worst-case drought scenarios. A study by University of Washington scientists has warned of a 25 percent reduction.

Did you know ...

The Colorado River provides drinking water to more than 25 million people and irrigation to 2 million farm acres.

Source: Arizona Department of Environmental Quality

* Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com.

Source: Arizona Daily Star

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