[7] Early Forecast Tool Calls For Near-Average Water Year

While still sounding the alarm for global warming, some Northwest climate researchers are calling for a pretty much average water year in 2006. That was the message from an Oct. 26 meeting in Seattle, a day before some were to take part in a regional get-together on climate change, hosted by King County and billed as, "The Future Ain't What It Used To Be."

The affair, sponsored by the University of Washington's Climate Impacts Group, was a low-key meeting of researchers and water users who heard that the high-powered hydrologic experts are now using ESP to help them generate long-term forecasts, but it's not the kind found in old late night TV shows. ESP stands for Ensemble Streamflow Prediction, a way to predict future water supply that starts with current soil conditions, and then adds past precipitation and temperature data to produce simulated flow scenarios.

The good news so far is that the Oct. 1 forecast (for April-Sept.) calls for the water year at The Dalles to be at 95 percent of average, about 97 percent at British Columbia's Mica Dam on the Columbia, and better than average, about 103 percent, at Montana's Libby Dam on the Kootenai River. Snake River flows at Hells Canyon are expected to be about 80 percent of normal, while southern Idaho rivers may see flows in the 45-percent to 60-percent range.

A forecast based on data from the National Weather Service's Climate Prediction Center is more optimistic, though the agency's official water supply forecasts won't begin until December. It calls for 104 percent of average flows between next April and September at The Dalles, 104 percent at B.C.'s Mica, and about 108 percent of average at Libby. Lower Snake River flows are pegged around 115 percent of average, and southern Idaho flows more than 120 percent of average. The CPC forecasters are saying that the next three months should see warmer-than-normal temperatures throughout the West, but neutral El Nino conditions should remain in place for the next 6 to 9 months.

But the ESP factor is only part of an ambitious experimental forecast system developed at the University of Washington that was described at the meeting last week. The big model uses forecast data sources such as NOAA and NASA, along with a dash of El Nino data and information on the Pacific Decadal Oscillation to create the final product dubbed the VIC hydrology model, or variable infiltration capacity macroscale hydrologic model.

Still one of the main conclusions from UW researchers Alan Hamlet and Andy Wood was not exactly a barn burner--they said it's early in the year for making water forecasts, especially in an ENSO-neutral year when signs of either El Nino warming or La Nina cooling are lacking. They said most Pacific Northwest basins are still on the dry side by 3 percent to 10 percent, with exceptions being the south edge of the Snake River and B.C. Because of higher rainfall, westside basins in the Cascades are more likely to recover from "moisture deficits."

That may already be happening since the weather service's River Forecast Center reports that October precipitation above Grand Coulee has been 147 percent of average, 117 percent of average at The Dalles, but only 92 percent of average on the Snake River above Ice Harbor. September was wet as well in many basins, where some like the Flathead in Montana received nearly 200 percent of average precipitation.

The UW's Matt Wiley gave the Puget Sound region "a forecast of average conditions, with a good chance of everything else." Describing how the region snapped out of a serious water deficit earlier this year, he said, "ten or twelve inches of rain between March 1 and July 1 can sure solve a lot of problems."

Eric Salathe, UW researcher, believes humans are partly responsible for the change in climate, particularly in the last 30 years. He said some climate models show a decrease in future precipitation by the 2020s. But it's more likely that with more warming in summer than winter, precipitation changes are uncertain, though it is possible that winters will be wetter and summers drier than now. "We are entering unknown territory," Salathe said, noting that most climate modelers expect temperatures to increase between 3 and 11 degrees F by 2100.

The climate change meeting slated for the following day was a mix of speakers and discussion groups, where breakout sessions were designed to tackle tough questions about coping with a future of reduced snowpacks, early runoff, increased winter flows and decreased summer flows.

Groups met to discuss specific problems for hydropower, agriculture and fisheries that may occur if things warm up as much as many expect, possibly three degrees F by the 2040s in the Northwest, and twice that by the 2080s, when precipitation could go up as much as 18 percent. Electrical production may have to shift toward renewables, nuclear or thermal, while reservoir operations may have to be adjusted, more conservation efforts begun, or even more dams built.

Salmon stocks could suffer from increased water temperatures, and some folks are already stumping for the integration of climate change information into salmon recovery planning. NOAA Fisheries scientists are working with the UW's Climate Group to look into the impacts of a changing climate on fish recovery alternatives being developed in Puget Sound's Snohomish Basin. Participants said that by comparing expected results from a range of management options, federal scientists could choose the plan that would have the best survival benefits for ESA-listed stocks, like local chinook.

One study dealing with Columbia River salmon (Columbia River Inter-Tribal Fish Commission, 2004) reported by session planners says earlier reservoir refill and more water storage could help managers reach flow targets and mitigate some negative effects from climate warming, but such a strategy could reduce power production up to 35 percent.

Another session was slated to discuss future impacts of climate change on the agricultural sector, where irrigation water may become scarcer. A study has predicted that water for irrigation in the Yakima Basin could decrease by 20 percent to 40 percent in the next 50 years. -B. R.

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