Friday, September 23, 2005
Copyright © Las Vegas Review-Journal

Global warming's effect on river flow examined

Global warming is almost certain to change the way the Colorado River flows, but rising temperatures do not appear to present a direct threat to Southern Nevada's primary source of water.

During a conference Thursday in Las Vegas, researchers said there is no clear evidence that global warming will result in less precipitation along the Colorado River.

Though higher temperatures could cause Rocky Mountain snow to melt earlier in the year, the researchers said the water still will find its way to the river and its twin reservoirs of Lake Powell and Lake Mead, from which the Las Vegas Valley draws 90 percent of its drinking water.

"It's not that we're getting less precipitation, but that less of it is falling as snow," said Dr. Michael Dettinger, research hydrologist for the U.S. Geological Survey.

But that does not mean the Colorado and the people who depend on it are safe from the effects of climate change. "With all this water leaving the basin early, you end up with a much drier basin in the summer," Dettinger said.

That can lead to any number of problems, including increased demand for water and frequent and potentially severe flooding, he said.

Dettinger's comments came during the two-day conference called "Urban Water Supplies and Climate Change in West."

Dr. Martin Hoerling led off the conference with an overview of the latest research on climate change. The meteorologist for the National Oceanic and Atmospheric Administration's Climate Diagnostic Center in Boulder, Colo., said there is now ample evidence that global climate change is being fueled by human emission of greenhouse gases.

"It is the rate at which things are changing that should be alarming us, not that it's a few degrees warmer than it used to be," he said.

Based on current modeling, average temperatures across the globe are expected to climb by three degrees over the next 50 years. That's enough to reduce the average snowpack by almost 60 percent in a coastal range such as the Cascades of Oregon and Washington, said Alan Hamlet, a scientist at the University of Washington in Seattle.

Dettinger said there is a perception that global warming is "a problem we are leaving to our children's children."

"Nothing could be further from the truth," he told the audience of about 50 climate experts and water managers. "We will be dealing with these problems before most of the people in this room retire."

"I think it's something we're going to have to look at," said Kay Brothers, deputy general manager for the Southern Nevada Water Authority. "The climate models now are so refined ... (they are) becoming more useful to water managers."

The conference, sponsored by the water authority, the Desert Research Institute and the New York-based nonprofit Natural Resources Defense Council, will end today after a 10:15 a.m. panel discussion moderated by water authority General Manager Pat Mulroy.