Drought, warming hit Wyo's water supply
PHIL WHITE Star-Tribune correspondent | Posted: Friday, October 6, 2006 12:00 am
LARAMIE - Recent drought and climatic warming, whether natural or human-caused, are having significant effects on Wyoming's water supplies, the deputy state engineer said at a water conference at the University of Wyoming Thursday.
Harry LaBonde said the drought has forced his office to restrict water use on some streams that have not been regulated in many years, if ever, and to enforce restrictions sooner in the season.
He said that only unusual precipitation in the Colorado River's lower basin avoided a "call" upon the upper basin states in 2005 pursuant to the Colorado River Compact, which allocated certain amounts of water to each of the states along the Green and Colorado rivers. LaBonde said that Lake Powell in southern Utah, which stores water to meet demands of the downstream states, was at only 38 percent of capacity in 2004, down from 94 percent in 1999.
Mike Besson, director of the Wyoming Water Development Commission, said Wyoming should expect to see 30 percent less water in the not-too-distant future.
"This is frightening," he said. "We will have to reduce our use."
One way to do that, he said, is to substitute wind-generated electric power for coal-fired generation, which requires large amounts of water for cooling. Besson also mentioned a system used in Arizona where water is spread over alluvial layers and soaks in, returning to the system later.
He said groundwater will become a more important source of water as the climate changes. "The next big hurdle will be quantifying the groundwater," he said.
Several speakers said the higher temperatures being experienced in recent years have caused an earlier runoff of mountain snowpack, which means less water is available during crucial parts of the growing season. Besson said the water has been coming off about 35 percent sooner than historic levels.
He also said the state needs to move forward with reservoirs to retain more water in the state, especially in the Green River Basin. He said his office began evaluating 24 opportunities for dams in 2000 and has identified two proposals as the most promising for increased storage in the Ham's Fork drainage of the Green River: raising the Viva Naughton dam and placing a new dam in the Dempsey Basin.
State climatologist Steve Gray said Wyoming is the fifth-driest state in the nation, averaging only 6 or 7 inches of precipitation per year in the basins of the southwest quarter. Wyoming is in the seventh or eighth year of a severe drought, he said, which has exposed the vulnerabilities of the state's water supply.
"The majority of the water comes from a single source, mountain snowpack," Gray said, "and the mountains comprise only about 7 percent of the state's land area."
Gray said scientists agree that global warming is at least in part due to human activities such as burning fossil fuels, deforestation and urbanization.
"If we continue with business as usual," he said, "scientists predict that temperatures will rise up to 6 degrees Celsius."
Very small changes in average annual temperatures can have large effects on water use in Wyoming, he said.
Noting that some scientists predict increased precipitation in Wyoming from the temperature increase, Gray warned that the increase in evaporation from a rise of only 2 degrees in temperature would offset a 15 to 20 percent increase in precipitation. That kind of warming, he said, would cause more of the state's precipitation to come in the form of rain instead of snow, further reducing the storage effect of snowpack.
Gray said tree ring studies of streamflow in the Colorado River show huge fluctuations over the past 1,100 years. However, the levels of precipitation enjoyed by that drainage in the 20th century, before the onset of the drought, were far above the historic means, he said.