Getting nerdy with sea level in the Pacific Northwest

A few weeks back I gave the webinar above on a new approach we are using to project future sea level in a climate change adaptation planning project I am involved in focusing on Clallam and Jefferson Counties in Washington State. The approach takes advantage of a new synthesis of sea level rise projections published last year.

Despite struggling with how to most effectively communicate probabilistic sea level rise projections, I'm really liking this new approach, and its got me thinking about how to do an even better job of incorporating and communicating the current and future hazard related to sea level processes. In the webinar, though, I highlight a few outstanding needs - gaps in research or data needs that are limiting our ability to be as rigorous we can possibly be with assessing contemporary and future hazards related to sea level and coastal impacts.

As an example, consider that these sea level rise projections are meant to get at the "still water level" (i.e. ignoring waves). In general we've viewed that as an okay first-order approximation of the hazard in the inland waters of Washington State...but is it?

First consider the photo above, which comes from Cliff Mass's Weather Blog (check out the specific blog here), but that he attributes to the West Seattle Blog. This photos was taken on 17 December 2012, when the water level, as measured by the NOAA tide gauge in Seattle, reached 14.47 feet relative to MLLW:

This water level was just shy, by a whisker (0.01 feet to be exact) of the record water level measured in Seattle on 27 January 1983.

Next consider this photo, taken at the same exact spot by Melissa Poe of Washington Sea Grant on 29 November 2014:

On this day, still water level reached just 13.11 feet:

Well shy of the near record water level of 14.47 feet associated with the event from 17 December 2012...yet the flooding extent is essentially the same. The obvious difference? A local wind storm generating waves:

So what this tells me is that the data that we derive from tide gauges, and that we use to assess the coastal flooding hazard now and in the future only tells us part of the story, and we need better information on waves in order to take things to the next level. This is nothing new, Peter Ruggiero and others have been telling us for years that we need to account for "total water level"...including the influence of waves. But largely that message has focused on the substantially more energetic wave climate of the outer coast of the Pacific Northwest. Clearly we need to account for waves in the inland waters as well. Now, if only we had data...