[3] UW Study Says Dams Could Cope With Climate Change
A new computerized crystal ball developed by climate scientists from the University of Washington and the Corps of Engineers says future dam operations could cope with big changes in the Columbia Basin they expect by 2060--much less snowpack and earlier melt in some places---to maintain an adequate power supply and reasonable flood protection.
The modeling effort was explained in the latest issue of the Journal of Water Resources Planning and Management. It took a broad-brush approach, using a monthly-time series, and found that dam operators could begin refilling some reservoirs up to a month earlier than current operations call for, and hold water longer to cope with the warmer climate they expect to see 50 years from now.
Lead author Alan Hamlet, a UW research assistant professor of civil and environmental engineering who works with the UW's Climate Impacts Group, is an expert in Northwest hydrology. He helped write the 2009 report about future climate impacts to the state of Washington, which estimated the state's snowpack will decline by 40 percent by the 2040s from the 1916-2006 average. However, the report said, overall precipitation is not likely to change much.
"There are anticipated dramatic changes in the snowpack which ultimately will affect when the water comes into the Columbia's reservoirs," Hamlet said, in a Jan. 21 statement that accompanied the article's release. "Changes in flood control operations constitute only one climate-change adaptation strategy, but our study shows that incorporating climate change in flood management plans can improve the performance of existing water systems in future climates."
The analysis is based on future temperatures that were developed by the Intergovernmental Panel on Climate Change, which estimated a 2 degrees Celsius increase by the 2050s.
The paper noted that each reservoir had its unique qualities. With more warming expected in Idaho than at other reservoirs, operational changes at Dworshak Reservoir would be more drastic than those at Montana's Libby project. The authors estimated Dworshak refill would have to begin a month earlier than it does now, while refill timing at Libby would be close to current operations.
With the expectation of less snow and peak spring flows, overall flood risk would decline in some places, said Se-Yeun Lee, a UW post-doc who worked on the analysis for her doctorate. "With reduced flood risk we can release less water and refill earlier," she said. "As a result, we can supply more hydropower in summer and more storage for other needs like fish flows."
The paper concluded that the existing infrastructure can work successfully in the future if changes are made in the way flood rule curves are generated: "The simulation results using the optimized flood rule curves demonstrate that additional trade offs between reservoir refill and flood control may be possible if flood risks like those experienced in the 20th century are acceptable, because the optimized flood rule curves show reduced flood risk."
The authors said they were continuing to refine their analysis to test for flood impacts at daily time scales.
However, their analysis may be overestimating future snowpack loss and timing of peak spring flows, according to a recent paper by other UW atmospheric researchers (Stoelinga et al), which has pegged snowpack losses in the range of only 2 percent per decade. They say it's likely snowpack declines are mitigated by a cool North Pacific Ocean, which may dampen overall effects of global warming in the Northwest.
If this analysis proves correct, snowpack losses would only be about one-third to one-fourth of the levels that were modeled in the new Hamlet et al. paper, and operations at dams would not have to change nearly as much as the new paper suggests.
But Hamlet isn't too impressed with the Stoelinga paper's results. "Right now this study is something of an outlier," he told NW Fishletter by email. "It doesn't mean they are wrong, but it requires some follow up to better understand the differences between their methods and those used in previous studies." He said "follow on studies are needed to see if the results are robust or just artifacts of the particular downscaling and analytical methods they chose."
Another new paper involving a UW researcher says the earth has warmed much less than climate modelers expected.
In a Jan. 19 study published online in the American Meteorology Association's Journal of Climate, Stephen Schwartz of the Brookhaven National Lab, Robert Charlson of the UW and their co-authors say global climate models estimate the earth's mean temperature should be up nearly 4 degrees Fahrenheit from fossil fuel use since the industrial era began. But only a 1.4-degree increase has been observed.
"The data show that either we have 40 years of emissions left before the atmosphere can't absorb any more carbon dioxide, or we're already past the point of no return. In other words, the uncertainty rate is unacceptably high," said Charlson, a professor of atmospheric sciences.
The new paper says the discrepancy between the observed and modeled temperature increase comes from two factors. First, the climate may be less sensitive to greenhouse gases than currently assumed, and/or reflection of sunlight by haze particles in the atmosphere could be offsetting some of the expected warming.
They said another factor might be the slow response of temperature to the warming influence of the gases, but they found this so-called "thermal lag" is likely only a minor influence.
Their paper also said that their most optimistic analysis suggests that it would take another 35 years of present-day levels of fossil fuel emissions to reach the IPCC's 3.6 degrees Fahrenheit threshold the panel regards as the dangerous level of human interference on climate.
But we may already be over the edge.
"These results do not in any way reduce or remove the need for solid action now to move toward a zero-carbon dioxide emission economy," said Charlson. "The results tell us that doing our utmost now might work very well if the most optimistic values of sensitivity are real, but that it is possible that nothing will work no matter how hard we try."
He said if uncertainties like gauging the effects of haze particles aren't reduced, "we will be in the same boat 10 or 20 years from now as we are today." -B. R.
The following links were mentioned in this story:
Optimized flood control in the Columbia River Basin for a global warming scenario
NW Fishletter #270, January 21, 2010
Why Hasn't Earth Warmed as Much as Expected?
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