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River Operations In Review: Will Early Runoff In Columbia River Basin Be The New Normal?
Posted on Friday, December 09, 2016 (PST)

As a contrast to especially warm and dry conditions in 2015 throughout the Columbia River basin, 2016 started off with a “reasonable snowpack,” but a warm April melted snow at a record pace resulting in an early runoff, according to a report from the Northwest River Forecast Center.

 

“The timing of the runoff from what is normal was a sure sign that we were losing our snowpack too early, which would leave us high and dry through the summer,” Kevin Berghoff of the NWRFC told the Technical Management Team this week at its Year End Review, December 7.

 

TMT is made up of fisheries and hydro/reservoir managers from state, federal and tribal agencies. Every December the group looks back at actions taken during spring and summer in managing Columbia and Snake river federal hydro/fish operations.

 

Berghoff’s presentation was among eleven others reviewed in Portland during the day-long session.

 

The seasonal precipitation this year (October 1, 2015 to September 30, 2016) was better than in 2015, one of the worst water years on record, but not in every place, Berghoff said.

 

In 2015, precipitation in much of the region was 70 to 90 percent of normal, whereas in 2016 most of the region was 90 to 110 percent of normal, December through March. Still, he said, there were plenty of areas in the region that remained at the 2015 levels for precipitation, including in the upper Snake River basin (see Berghoff’s presentation at http://www.nwd-wc.usace.army.mil/tmt/agendas/2016/1207_Agenda.html).

 

Precipitation began to decline earlier than normal. By April and May, much of the Snake River basin was at 70 to 90 percent of average precipitation, and the Kootenai River basin in Montana was below 50 percent precipitation.

 

Temperatures were 3 to 6 degrees and more higher than normal in 2015, and February and April 2016 saw similarly large departures from normal temperatures, leading to the early runoff.

 

Those warm April temperatures depleted the snowpack, Berghoff said. By May, most SnoTel sites (snowpack measuring stations) were at less than 50 percent of normal and there was little runoff potential left.

 

“We’ve had an early runoff two out of the last five years,” Berghoff said. “While that is not a trend, it does begin to make the case for a ‘new normal.’”

 

He said the last two years have been unique. However, 2016 was due to higher sea surface temperatures, while 2015 was due to “The Blob,” a large pocket of warm water that persisted in the northern Pacific Ocean from 2013 to late 2015.

 

Kyle Dittmer, meteorologist with the Columbia River Inter-Tribal Fish Commission, said that the region is currently experiencing a “border-line” La Nina to neutral conditions, which tends towards weather with more variability.

 

Berghoff added that weather would tend to be cooler and wetter.

 

Precipitation in the Columbia River basin above The Dalles Dam was higher than normal in December and March, slightly below normal in January and February and, at just 63 percent of normal, significantly below normal, in April.

 

Temperature departures in the same area, December through April, were consistently above normal, reaching the highest departures from normal in February and April at 5.2 degrees Fahrenheit and 5.5 degrees F above normal.

 

Runoff volume during the December through April period followed rainfall and eventually snow melt, with runoff estimates at The Dalles of 109 percent of normal in December, near normal runoff in January and February, and runoff increasing to 130 percent of normal in March and 157 percent of normal in April, the month with the most runoff, and then falling to 63 percent of normal by June.

 

Water supply, April to September in the Kootenai River basin at Libby Dam was 91 percent of normal. It was 86 percent of normal at Hungry Horse Dam, 84 percent of normal at Dworshak Dam and 89 percent of normal at The Dalles Dam.

 

Also see:

 

--CBB, September 16, 2016, “La Nina Prediction For Northwest Winter Now Neutral, Could Mean Warmer-Than-Average Temperatures,” http://www.cbbulletin.com/437537.aspx

 

--CBB, July 15, 2016, “Study: The Warm-Water ‘Blob,’ Combined With El Nino, Depressed Marine Productivity Off West Coast,” http://www.cbbulletin.com/437129.aspx

 

-- CBB, April 10, 2015, “‘Warm Blob’ Of Water Off West Coast Linked To Warmer Temps, Disruption Of Marine Food,” http://www.cbbulletin.com/433648.aspx

 

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