As the Earth warms, experts know the Columbia will change – they just don’t know how much or when.

91̽»¨ environmental engineers are launching a new study to try to understand how climate change will affect streamflow patterns in the Columbia River Basin. The team will look at the impact of glaciers on the river system, the range of possible streamflow changes and how much water will flow in the river at hundreds of locations in future years.

“Getting a new set of streamflow predictions factoring in climate change will help guide long-term decision-making for the Columbia River Basin,” said , a 91̽»¨professor of civil and environmental engineering. He is leading the project with , 91̽»¨researcher in civil and environmental engineering, and of Oregon State University.

The Columbia River’s headwaters are in the Rocky Mountains of British Columbia, and the waterway winds about 1,200 miles through Washington and along the border of Oregon before emptying into the Pacific Ocean. Hydroelectric dams provide cheap electricity to roughly three quarters of the Pacific Northwest’s population and help with flood control throughout the basin, particularly in the Portland metro area. It’s also an important waterway for migrating salmon, steelhead and sturgeon, and for navigation, irrigation and agriculture.

Changes in streamflow due to climate change could affect hydropower and flood control operations on the Columbia as well as fisheries management and future policy decisions, including a possible treaty renegotiation between the U.S. and Canada.

The 91̽»¨researchers will use the most recent projections from the Intergovernmental Panel on Climate Change along with climate and hydrology models to come up with a dataset of streamflow predictions for Bonneville Power Administration, the U.S. Army Corps of Engineers and the Bureau of Reclamation, which jointly commissioned this study. The Bonneville Power Administration’s Technology Innovation Office, Oregon State University and the 91̽»¨are funding the study, which leverages glacier model developments from a NASA-funded interdisciplinary science project.

“Hopefully, this study will be able to better bracket the uncertainty that exists methodologically between all these climate and hydrology models. If we want to be able to plan ahead on a 20- to 50-year timescale, we need to know what range of uncertainty to expect,” Nijssen said.

The impact that declining glaciers could have on the basin hasn’t fully been studied by U.S. scientists until now, though Canadian researchers recently started to look at their role. Glaciers are receding across the region and, as temperatures warm, they will continue to melt and erode. In 2005, glaciers covered about 420 square miles in the upper reaches of the Canadian Columbia Basin, or roughly 5 percent of that area. Twenty years before glaciers covered 490 square miles.

Melting glaciers put more water into the river system and boost its flow, but only for a period. This short-term boost could actually benefit the river – especially during low-flow periods in the drier summer months – but only in the short term. As the glaciers eventually disappear, perhaps as early as 2100, this added water will also disappear and further reduce already low summer flows, researchers say.

But the river’s yearly flows depend mostly on melting snowpack. Cooler spring and early summer temperatures can preserve mountain snowpack until the drier months, when water from melting snow is important to keep river flows high enough for migrating fish. As the climate warms, though, the timing of when that crucial snow melts and discharges into the river also is likely to change.

“The hydrology of the Columbia River basin is really driven by winter snow accumulation and melting in the spring and summer months. When it warms up, you change that balance,” Lettenmaier said.

The UW’s data could have policy implications for the Columbia River. Since 1964, a treaty between the U.S. and Canada has governed the river for hydropower production and flood control. But starting in 2014, each country can notify the other of an intent to terminate or modify this treaty. Changes to the treaty could be implemented as early as 2024.

“We want to have the best scientific information possible to help federal agencies and other regional stakeholders in long-range decision-making,” said Erik Pytlak, manager of the weather and streamflow forecasting for the Bonneville Power Administration. “With or without a treaty, climate change is coming. It will be beneficial for all of our partners and customers in the region to have an updated understanding of what climate change is doing to the region.”

The UW’s streamflow predictions will be publically available after the study is finished in three years. Similar studies are underway at Portland State University, also funded by Bonneville, and by climate scientists in Canada.

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For more information, contact Lettenmaier at dennisl@uw.edu or 206-543-2532 and Nijssen at nijssen@uw.edu.

In the past five years, scientific studies estimated declines of future flows ranging from 6 percent to 45 percent by 2050. A paper by 91̽»¨ researchers and co-authors at eight institutions across the West aims to explain this wide range, and provide policymakers and the public with a framework for comparison. The is published this week in the .

“The different estimates have led to a lot of frustration,” said lead author , who recently earned a 91̽»¨doctorate in civil and environmental engineering. “This paper puts all the studies in a single framework and identifies how they are connected.”

Besides analyzing the uncertainty, the authors establish what is known about the river’s future. Warmer temperatures will lead to more evaporation and thus less flow. Changes to precipitation are less certain, since the headwaters are at the northern edge of a band of projected drying, but climate change will likely decrease the rain and snow that drains into the Colorado basin.

It also turns out that the early 20^th century, which is the basis for water allocation in the basin, was a period of unusually high flow. The tree ring record suggests that the Colorado has experienced severe droughts in the past and will do so again, even without any human-caused climate change.

“The Colorado River is kind of ground zero for drying in the southwestern U.S.,” said co-author , a 91̽»¨professor of civil and environmental engineering. “We hope this paper sheds some light on how to interpret results from the new generation of climate models, and why there’s an expectation that there will be a range of values, even when analyzing output from the same models.”

The authors include leaders in Western water issues, ranging from specialists in atmospheric sciences to hydrology to paleoclimate. Other co-authors are at the University of Colorado in Boulder; , Tapash Das and Hugo Hidalgo at the University of California, San Diego; , Holly Hartmann and Kiyomi Morino at the University of Arizona in Tucson; Levi Brekke at the federal Bureau of Reclamation; at the U.S. Geological Survey in Denver; and Martin Hoerling at the National Oceanographic and Atmospheric Administration in Boulder; and Kevin Werner at the National Weather Service in Salt Lake City.

The authors compared the array of flow projections for the Colorado River and came up with four main reasons for the differences. In decreasing order of importance, predictions of future flows vary because of:

• Which climate models and future emissions scenarios were used to generate the estimates.
• The models’ spatial resolution, which is important for capturing topography and its effect on the distribution of snow in the Colorado River’s mountainous headwaters.
• Representation of land surface hydrology, which determines how precipitation and temperature changes will affect the land’s ability to absorb, evaporate or transport water.
• Methods used to downscale from the roughly 200-kilometer resolution used by global climate models to the 10- to 20-kilometer resolution used by regional hydrology models.

While the paper does not determine a new estimate for future flows, it provides context for evaluating the current numbers. The 6 percent reduction estimate, for example, did not include some of the fourth-generation climate model runs that tend to predict a dryer West. And the 45 percent decrease estimate relied on models with a coarse spatial resolution that could not capture the effects of topography in the headwater regions. The analysis thus supports more moderate estimates of changes in future flows.

“Drought and climate change are a one-two punch for our water supply,” said Overpeck, a professor of geosciences and of atmospheric sciences at the University of Arizona.

The new paper is intended to be used by scientists, policymakers and stakeholders to judge future estimates.

“I hope people will be able to look at this paper and say, ‘OK, here’s the context in which this new study is claiming these new results,'” Vano said.

The research was funded by NOAA through its and its National Integrated Drought Information System.

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For more information: Vano: 206-794-7946 or jvano@uw.edu; Lettenmaier: 206-543-2532 or dennisl@uw.edu; Overpeck: jto@email.arizona.edu; Udall: 303-492-1288 or bradley.udall@colorado.edu