Thursday, January 20, 2011

"King" tides in Edmonds, WA

An increasing probability of coastal flooding due to extreme high tides is one of the impacts of climate change in the Pac NW that we should consider. Here is a brief from today's Seattle Times regarding Edmonds preparations for expected high tides this weekend.

They mention in the paper that these "king" tides occur once or twice a year. The astronomical components of water level, controlled primarily by the relative position of the sun and the moon, do indeed combine a few times a year in such a way to produce extremely high (and low) water levels. Usually communities are relatively well prepared for the astronomical component of king tides, since they are regularly occurring and predictable.

The trouble for coastal communities occurs when some climatic or oceanographic event adds more water on top of the already high water levels. In this article the additional water is attributed to precipitation. Sea level rise will also add elevation to the peak water levels. In Puget Sound strong winds in the Pacific Ocean can also push water into the inland sea, raising the overall water level. Finally, we must consider that waves (even the wind waves generated in Puget Sound) can increase the destructive force of high water.

Much of our region is still in a pattern of post-glacial rebound, which ameliorates to a degree the influence of pure or "eustatic" sea level rise. Relative sea level in some parts of the Salish Sea is, in fact, dropping rather than rising (Neah Bay, for example) because of high rates of tectonic uplift. We also have a tendency to think of sea level rise in rather simple terms, as a bit more water filling the tub. The real question for our region is a bit more complex: "How will the probability of occurrence of "king" tides increase over the next 10 to 100 years as sea-level increases and storm and precipitation patterns change?". In other words, will we see more articles like this one, in more places, over the coming years?

No comments: