A new sea level rise impact assessment hits the news...but may not be newsworthy

A few days ago the Center for Climate Integrity released quite an interesting study intended to try to estimate the cost of protecting the nation's coastlines against sea level rise using shoreline armoring approaches.  I was interviewed for a response, as were other colleagues within the Washington Coastal Resilience Project, and collectively I think we pushed a few key points in response to this study:

1.  On the plus side:  The overall benefit of studies like this, from my standpoint, is to both remind us that there are impacts to things we care about from sea level rise, and to come up with comparative cost/impact estimates for sea level rise across some area of interest (the United States, Washington State, etc.).  Put another way, studies like this can provide us with ways to prioritize different adaptation actions over some area we care about.  An example of a similar study is Zillow's real estate exposure analysis analysis from a few year's ago.  I didn't look at Zillow's analysis as a real prediction of real estate impacts, but I DID see it as a useful way to evaluate relative vulnerability to sea level rise across the country, and across Washington State.  That is useful.

2.  Also on the plus side:  They do a good job focusing on the near-term.  They emphasize in their results that they are using a sea level rise scenario that is likely by 2040.  That is very much within contemporary planning horizons.  That is useful.

3.  Now, on the negative side:  This study SHOULD NOT lead anyone to imagine though that armoring is the only, or the most desirable, way to address sea level rise.  Lest you imagine that we were alone in this response, my friend and colleague Rob Young in North Carolina had the same response.  There are a variety of possible responses to sea level rise, including adaptating vulnerable infrastructure, or pulling it back from the coast, or soft-shore armoring options, that may very well be cheaper AND more effective than traditional armoring for reducing risks from sea level rise.

3.  And also, on the negative side:  There may be some flaws in this study.  I didn't outright say this in my interview, mostly because at the time I had barely had a chance to review the report.  But now that I've had a chance to dig into it a bit more I can't really figure out where they got the numbers they did.  Setting aside the question of how accurate the dollar values are, this  also compromises the usefulness of this study as a way to assess relative vulnerability along the coast.  To be clear, the methods they outline seem sound...but let me illustrate my concerns.

Here is a map of the contemporary Mean High High Water shoreline of Port Angeles, snipped from the NOAA Sea Level Rise Viewer:

So the blue areas are those that are currently flooded at the current average high tide.  I chose Port Angeles to focus on for two reasons:  First, this is where I live, so I know the shoreline really well.  Second, Port Angeles pops out in their analysis as one of the most exposed communities on Washington's coast, requiring 15 miles of seawalls to provide protection by 2040, under the scenario that they considered.

Okay, so lets dig into that a bit.  First, 15 miles is a lot.  Measuring the length of shorelines is hard and you get different numbers doing it different ways.  BUT, I did a quick and dirty assessment of the TOTAL shoreline length for the city of Port Angeles using Google Earth and came up with...12.5 miles.  Total:

I don't get all of the tiny little wiggles and such, but I do include the bluff backed shoreline to the east of Port Angeles.  So at first blush 15 miles of seawall "required" by 2040 seems quite a lot. .

I also mapped, again using the NOAA Sea Level Rise Viewer, their chosen scenario for their analysis, a 50th percentile sea level rise projection for 2040 under RCP 4.5 (I came up with 5 inches) and a 1-year return frequency storm surge event (1.5 feet)  Here is the map:

Compare this carefully with the map above and look for differences.  See any?  There are a few but they are VERY slight.  There is a good physical reason for this...we have a steep shoreline, and we already get plenty of events the push water 2 feet above MHHW.  As a consequence, there isn't much built in that zone.  How did their model translate this into a change into a changed flood exposure that "requires" armoring the entire coast of Port Angeles? 

Before I look to a study like this as a useful way to assess relative vulnerability to sea level rise on Washington's coast I have to understand that.