Uncertainty and Extreme Events in Future Climate and Hydrologic Projections for the Pacific Northwest: Providing a Basis for Vulnerability and Core/Corridor Assessments

Jeremy S. Littell, Guillaume S. Mauger, Eric P. Salathe, Alan F. Hamlet, Se-Yeun Lee, Matt R. Stumbaugh, Marketa Elsner, Robert Norheim, Eric R. Lutz, Nathan J. Mantua
Posted on: 7/18/2022 - Updated on: 3/03/2023

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The purpose of this project was to (1) provide an internally-consistent set of downscaled projections across the Western U.S., (2) include information about projection uncertainty, and (3) assess projected changes of hydrologic extremes. These objectives were designed to address decision support needs for climate adaptation and resource management actions. Specifically, understanding of uncertainty in climate projections – in particular for extreme events – is currently a key scientific and management barrier to adaptation planning and vulnerability assessment.

The new dataset fills in the Northwest domain to cover a key gap in the previous dataset, adds additional projections (both from other global climate models and a comparison with dynamical downscaling) and includes an assessment of changes to flow and soil moisture extremes. This new information can be used to assess variations in impacts across the landscape, uncertainty in projections, and how these differ as a function of region, variable, and time period.

In this project, existing University of Washington Climate Impacts Group (UW CIG) products were extended to develop a comprehensive data archive that accounts (in a reigorous and physically based way) for climate model uncertainty in future climate and hydrologic scenarios. These products can be used to determine likely impacts on vegetation and aquatic habitat in the Pacific Northwest (PNW) region, including WA, OR, ID, northwest MT to the continental divide, northern CA, NV, UT, and the Columbia Basin portion of western WY New data series and summaries produced for this project include: 1) extreme statistics for surface hydrology (e.g. frequency of soil moisture and summer water deficit) and streamflow (e.g. the 100-year flood, extreme 7-day low flows with a 10-year recurrence interval); 2) snowpack vulnerability as indicated by the ratio of April 1 snow water to cool-season precipitation; and, 3) uncertainty analyses for multiple climate scenarios.


Littell, J.S., Mauger, G.S., Salathé, E.P., Hamlet, A.F., Lee, S-Y., Stumbaugh, M., Elsner, M.M., Norheim, R.A., Lutz, E.R., Mantua, N.J. 2014. Uncertainty and Extreme Events in Future Climate and Hydrologic Projections for the Pacific Northwest: Providing a Basis for Vulnerability and Core/Corridor Assessments. Final report for Department of the Interior Pacific Northwest Climate Science Center. Climate Impacts Group, University of Washington, Seattle, WA.

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The University of Washington Climate Impacts Group builds climate resilience by advancing understanding of climate risks & enabling science-based action to manage those risks. We are widely recognized for scientific discovery, as an experienced creator of impartial & actionable science and as a catalyst for building regional climate resilience.

Established in 2010, the Northwest CASC (NW CASC) provides regionally-relevant scientific information, tools, and techniques to resource managers and communities in Washington, Oregon, and Idaho. Its purpose is to provide scientific information, tools, and techniques that managers and other parties interested in land, water, wildlife and cultural resources can use to anticipate, monitor, and adapt to climate change.