How to Choose: A Primer for Selecting Sea Level Rise Projections for Washington State

Crystal Raymond, Nicole Faghin, Harriet Morgan, Heidi Roop
Created: 7/30/2020 -


As global sea levels rise — and preparing for these and other consequences of climate change increases in priority — we have seen an increasing demand for detailed local sea level rise projections and for guidance that supports their use in planning, policy development and project design. Recognizing gaps in existing sea level rise (SLR) information for Washington state, in 2018 a team of scientists developed updated projections for Washington’s coast under the auspices of the Washington Coastal Resilience Project (WCRP).

These projections show a range of SLR magnitudes that Washington state could experience, associated with different potential climate change futures driven by society’s choices about greenhouse gas emissions. The 2018 SLR projections provide more insight into the potential range of SLR that Washington state could experience than has been available before, bringing new information to potential users. However, using these projections requires careful consideration of certain choices described in this primer when selecting values to use in planning and design.

This primer is designed to guide potential users of the 2018 SLR projections through the choices necessary to select and use SLR projections for their particular context. The intended audiences include coastal planners, engineers, climate adaptation specialists, restoration ecologists and others who seek more direction on how to use and choose from the 2018 SLR projections. Although the approach described here is intended to facilitate the use of the 2018 projections, it represents fundamental principles of selecting climate change scenarios for use in risk assessment, planning, and decision making, and could be applied in other locations with other datasets.

This primer provides information to assist the user with selecting from the range of projections for use in a variety of contexts including: (1) climate change or coastal vulnerability assessments and adaptation plans, (2) policies and plans for coastal management, (3) the design of projects in the built environment, and (4) the design of projects for nearshore restoration. The choice of which projections to use may differ in each context, but the process of choosing projections and the decisions that need to be made when selecting projections are similar for all contexts. We describe some factors to consider when making each of these choices:

  • Which of the 171 locations to use?
  • How to select relevant timeframes?
  • How to select appropriate probabilities?
  • Which greenhouse gas scenarios to use?

For each choice, we direct the user to the reports that contain more scientific detail on the projections and to a SLR data visualization that allows the user to explore the full range of projections. The primer begins with a brief description of the series of reports developed for the WCRP and the SLR data visualization. Section 2 provides an overview of how to use the SLR projections in combination with information on existing water levels to assess exposure to expected future water levels. Sections 3-6 describe some factors to consider for each of the necessary choices when selecting from the range of projections. Section 7 describes some additional options for visualizing and mapping SLR projections, which can be useful for the process of selecting projections, as well as for conveying information about selected projections to a broader audience.

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