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 Sea Level Rise (SLR) or Sea Level Change (SLC) - A Discussion and Background

OK, so this is one of the big stressors, both present and future, for life on Sullivan’s Island. I just wanted to lay the groundwork for what I will be doing in most of the sections in this website. In short, we can not know how bad a storm surge will be from year to year - we have to look at it statistically - but with SLR or SLC (either is fine) we have some good science to work from so we actually do have a good idea of what it will be in 20 to 40 years. After that, well, it gets a bit more cloudy.

We have all seen the graph above showing the monthly average (MSL) water levels in Charleston Harbor. It is reassuring, with a slope of 1 ft every century, but this is old science. I think with all we have dealt with in 2020 (Covid) we understand that linear is not always the way to look at things, so in this case, I don’t pay too much attention to the linear trend. The data is great, though.

I look at it from 1980 to present (about 40 years) and with the understanding that the trend is not linear (below). In this case there is a velocity term (kinda like linear) at 2.8 mm/yr and an acceleration term (0.00006 mm year^2). Note that the trend is lower than we have seen in the past couple of years so I would suggest it is a conservative assessment.

So, how does our local measured trend relate to all the curves out in the literature? Actually it is pretty much in the middle until about 2060 when different acceleration terms start to diverge fairly dramatically. As I mentioned above, the Charleston Curve (for lack of a better term) is likely a conservative one, so it is still very possible that the scenarios the higher curves portray are more in line with what the conditions will become. It is not very likely, however, that the curves too far below the Charleston Curve will be accurate for our island. In very plain language it suggests that by 2050 MSL will be right around 0.5 m higher on Sullivans Island than in 1992.

If you have gotten to this point good for you. I hope the information above gives you a practical feel, without going into the science of what is driving the change, of what magnitude we are looking at. The outcomes and processes that become affected are what I will be concentrating on.

That said, if you would like to continue on to how I am looking at change (coming up with risks) the information above will provide a good base. You can find the risk information HERE or in my BLOG where I go into a more complete discussion.