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NW Fishletter #388, Dec. 3, 2018

[1] Climate Change Study To Help BPA Prepare For Warmer, Wetter Columbia Basin

Imagine a Columbia Basin where February's biggest storm brings rain to the Cascade Mountains instead of snow, prompting the winter snowpack to begin melting, causing peak runoff three months earlier than usual.

Erik Pytlak can, but it's not in his imagination.

Pytlak manages the Bonneville Power Administration's Weather and Streamflow Forecasting group, and when he isn't predicting availability of water for power generation over the next three months, he's working on the longer-term question of climate change, and how warmer temperatures will impact the weather and streamflows in the Snake and Columbia rivers. For the past four years, he's worked with other federal agencies and universities to produce their most recent analysis on climate change in the Columbia Basin.

Released in June, with half the funding coming from Bonneville, the first part of the report, titled "Hydroclimate Projections and Analyses," will now be used in a second report analyzing how projected changes in temperature, precipitation, snowpack and streamflow will impact Columbia Basin hydropower through the rest of this century.

Pytlak gave a presentation to the Northwest Power and Conservation Council on Nov. 14, and answered follow-up questions the next day in an interview with NW Fishletter.

The report was produced by the River Management Joint Operating Committee--which includes BPA, Bureau of Reclamation and the U.S. Army Corps of Engineers--with help from research teams at the University of Washington and Oregon State University. It uses more recent data and modeling to update RMJOC's 2011 climate change study.

Among major findings: By the 2030s, the Columbia Basin will very likely experience higher average winter flows, earlier peak spring runoff and longer periods of low summer flows. "And what I mean by 'very likely' is a greater than 90 percent chance," Pytlak told the Council.

Columbia Basin temperatures have already risen by about 1.5 degrees since the 1970s, and the warming is forecast to continue, he said. The report predicts they'll increase another 1 to 4 degrees by the 2030s, with the greatest warming in the interior and less warming near the Pacific Ocean. If greenhouse gas emissions are curbed soon and drop by 2050, temperatures by the 2070s are likely to warm another 3 to 6 degrees compared with current observations, according to the study. If emissions continue increasing on the current trajectory, basin temperatures will rise by 4 to 10 degrees above current observations.

Forecast precipitation trends are more uncertain, but most models now show winters in the Columbia Basin are likely to get wetter throughout the rest of the century, and summers could get drier, especially in drier areas. The earliest and greatest streamflow changes are likely to occur in the Snake River Basin, where the study predicts a 20 percent to 30 percent increase in winter precipitation, Pytlak said. But the Snake River is also the part of the Columbia Basin with the greatest uncertainty, he said. That's because historical data--such as streamflows prior to irrigation--is more uncertain, and because the Snake River has a lot of surface and groundwater exchange, making it harder to model, he said.

"Uncertainty does not mean that climate change is uncertain. Climate change is quite certain," he told NW Fishletter. But the degree of change, the rate of change, and what those changes will do to the atmosphere and hydrology are uncertainties, he said.

The study developed 172 different scenarios, and 19 of those that capture a full range of possibilities will be used to examine impacts to the hydroelectric system, Pytlak said. He noted that BPA is responsible to continuously evaluate and anticipate risks in the Federal Columbia River Power System so it can be prepared for the future. "When is our water supply going to come? What does that mean in terms of generation? This is part of our understanding of risk, and it's our responsibility to understand all the risk," he said. "It allows us to prepare, and know where our strengths and weaknesses are."

Pytlak told the Council that atmospheric carbon dioxide is at its highest level in hundreds of thousands of years--and possibly in millions of years. Scientists believe that 3 million years ago, when CO2 levels were this high, the earth's temperature was 5 to 7 degrees higher than today, and sea levels were 60 to 80 feet higher, he said.

Pytlak said carbon dioxide isn't the only greenhouse gas of concern. Methane, which is many times more efficient in re-emitting heat energy, is also increasing, and included in the climate change models. He noted that this current round of warming has been rapid and constant since the 1980s.

Changes in snowpack will be the biggest regional impact from a warming climate. Pytlak said initially, precipitation in the Canadian Cascades is expected to continue as snow, but in the U.S., more and more winter storms will bring rain to the Cascade Range instead of snow. That will translate to higher streamflows from November through April, and sometimes, an earlier snowmelt and runoff or multiple peaks, he said. Summer will bring lower flows, partly due to the earlier runoff, but also because glaciers will provide less water as they continue to melt.

Pytlak added the study is designed to be of value not only to Bonneville, but to the entire Northwest as well as other regions. The information is available to all, and is already being looked at by other hydropower systems across the country, Pytlak said, adding, "This work is contributing to the national discussion on climate modeling and change."

In a briefing to the Council following Pytlak's, scientists from the Pacific Northwest National Laboratory put some of the warming trends from the study in context of the impacts to hydropower, and adequacy of the region's power supply.

Sean Turner, PNNL's water resources management modeler, and Nathalie Voisin, its regional water-energy dynamics research lead, outlined how multiple climate "events" occurring at the same time can affect energy reliability more than the impacts of each event, added together.

As an example, he said, a warming climate will likely result in increased power demand in the summer, as needs go up to cool buildings and pump water to irrigate crops and landscaping. "It might be that the system has enough redundancy to handle that," he said. In addition, the system may produce less hydropower in summer due to lower flows, and the system may be prepared to handle that as well, Turner said.

But, he said, in order to prepare for both changes at the same time, the region should be ready for a combined impact greater than the sum of both, he said.

Turner said their analysis shows that under one scenario, the changes will prompt inadequate supply due to low flows twice in 100 years, and an inadequate supply due to additional load five times in 100 years. But when both events occur simultaneously, supply will be inadequate 13 times in 100 years, he said. "If you want to be considering climate impacts to the system, you need to look at lots of different impacts, and simulate them at the same time," he explained. -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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