By Ian Miller, Washington Sea Grant
A few months ago Washington Sea Grant's Paul Dye put together a blog post for the CHRN describing the conceptual underpinnings of the Washington Coastal Resilience Project (WCRP). Now that the WCRP is a bit more than a year old, I wanted to provide a bit more detail on some of what we are doing as part of "Objective 1" of the project, which is focused on:
"Filling critical information gaps and improving the communication of risk about coastal hazards and related climate impacts (sea level rise, storm surge, wave impacts, and shoreline erosion) that hinder planning and action in Washington's coastal communities."
First off, let's be clear that for the WCRP we are primarily talking about flooding and erosion hazards related to sea level, storm surge, and waves, not tsunami hazards. The distinction is important since most Washington coastal communities are exposed to both varieties of hazard. With that distinction in mind, the fundamental idea behind Objective 1 was to try to improve the information available to Washington's coastal communities in order to advance planning associated with current and future coastal flooding and erosion hazards.
It is worth noting here that, via FEMA flood mapping, we already have reasonably good information on coastal flooding that communities use and rely on for planning and permitting-- the problem is that as sea level rises the characteristics (i.e., the magnitude or frequency of flooding, or the location or severity of erosion) of those hazards are likely to change. For those of us focused on Objective 1, we are trying to take advantage of, and translate, some new tools and insights from the scientific community that hopefully improve our ability to plan for this changing risk profile for Washington's coastal communities. I tend to lump what we are doing in Objective 1 into one of four big innovations:
1) Moving towards communicating the full range of possible sea level rise in a probabilistic framework, and away from using narrow "likely" ranges, or scenarios
2) Assessing vertical land movement around coastal Washington, at resolutions that allow us to create relative sea level projections that are robust for community use
3) Acknowledging that it's not just about mean sea level, but we really need to figure out the ways in which sea level rise influences extreme events and coastal flooding by integrating storm surge and wave impacts to create extreme water level projections
4) Trying to move towards including projected shoreline erosion, and not just future sea level or extreme coastal flooding, in sea level rise vulnerability assessments (in the same way that the Friends of the San Juans and Coastal Geologic Services did)
I won't delve into each of these here and now-- look for future blog posts. For now lets focus a bit more on #1-- communicating sea level projections in a probabilistic framework. What do we mean by that? Those interested in planning for sea level rise in Washington's coastal communities have leaned on a few previous assessments, most notably the 2008 "Mote Report" and the 2012 National Research Council's report on sea level rise for the west coasts of the United States. In fact, I was a partner on a climate change vulnerability assessment and adaptation planning process for the Jamestown S'Klallam Tribe in which we used projections from the National Research Council's report. We ran into an issue, though, in applying those projections to a sea level rise vulnerability assessment: a broad range of possible future sea levels are presented but with little in the way of tools that could help us to assess what magnitude of sea level rise to plan for. We ended up using three sea level scenarios adapted from the National Academy's projections, and created maps for each scenario...but couldn't give any guidance to the community in regards to the likelihood of each scenario that they could build into their vulnerability assessment.
For a subsequent project focused on Clallam and Jefferson Counties, we adopted a new "probabilistic framework" for sea level projections published in 2014 by Bob Kopp at Rutgers University. What this approach attempts to do is to provide a reasonable assessment of the full range of possible sea level rise, and also to assign probabilities within that range. The probabilities allow us to assess questions like, "What is the most likely future sea level for a particular emissions scenario, given the current state of the science?" or "What are the less likely, but still possible, higher ranges for sea level in the future, based on the current state of the science?" What we saw emerge from that effort were much more engaged discussions about community vulnerability to sea level rise, and new insightful conversations about the potential costs and benefits of particular planning or investment decisions in light of various possible future sea levels. I also believe that we saw a better understanding of the uncertainties associated with projecting future sea level (which are considerable). In sum: a deeper and more meaningful conversation about the future implications of sea level rise for Washington's communities.
We anticipate using the same approach for Objective 1 (and it's worth noting here that other communities around the country are moving in this direction. A recently released assessment for California used this same probabilistic approach to communicate updated projections). What do these projections look like? Well there are a variety of ways to try to summarize and visualize this sort of information. Here, for example, is a visual representation of projections for the RCP8.5 emissions scenario at a variety of different probabilities, coupled with an estimate of OBSERVED annual average water level for Washington State:
This is drawn from a sea level rise assessment for Island County that I was involved with. Note as well that this figure includes a comparison with projections from both the "Mote Report" and the National Research Council report referenced above. The range of uncertainty shown in this figure is large, especially as you move towards 2100-- in fact, you can compare the width of the uncertainty band to the projections from previous reports to see that the probabilistic framework communicates a much larger range of possible future sea level rise than was communicated in the past. Certainly the impacts to Washington's communities from sea level will be dramatically different if we see seven feet by 2100, versus two feet, versus 0.5 feet, all of which are possible. What the probabilistic format allows us to do, though, is to examine those implications in light of likelihood...something we couldn't fully do before.
Another way to represent this information is with a table. Here are the same projections as in the figure above (in feet) in table format:
This is considerably harder to wrap your head around...in fact I often refer to this as "the awful table"...but it is designed and intended to give maximum flexibility to a community for decision-making. A community could use this table to do their own mapping, or to see the most detail in terms of WHEN or HOW MUCH sea level change is likely. It's hard to wrap your head around, but once you do it provides the greatest insight about possible future sea level (again, based on this assessment of current science) across a range of dates and probabilities.
And finally, here is an example of a summary table for multiple emissions scenarios drawn from the California report linked above:
There is a lot to like about this summary approach. Notably it summarizes sea level rise information across a range of emissions scenarios, and also pulls out and summarizes some of the more relevant planning probabilities-- those in the most likely range, and also those in the "unlikely but higher impact" zones. Within our project team we are having a lot of discussions right now about the best and most effective ways to communicate these projections.
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