High Tides and Storm Surge Are NOT Sea Level Rising
In earlier parts of this series, we looked carefully at charts from the National Oceanic and Atmospheric Administration (NOAA) and found that sea level is rising only 1.7 millimeters per year along the northern New England coast.
That’s about the thickness of a credit card.
Many tidal stations along the coast show a slightly higher amount of sea level rising, maybe to 2 to 3 millimeters per year. That’s because the coast is actually sinking ever so slightly.
Turning these small amounts of rising into feet of rise over 100 years, we show that the sea level is only about 6 to 9 inches higher than it was a century ago.
How Did We Get Widespread Flooding in the Pre-Christmas Storm?
Here’s a satellite image of the storm as it developed and deepened over the eastern U.S. and Canada on December 23, 2022.
The National Weather Service (NWS) in Grey, Maine forecasted hurricane-strength winds blowing in from the ocean. These high winds would continue for several days, allowing seas to heap up and build as the waves reached the Maine and New Hampshire shores.
Combine Astronomically High Tides with Record Storm Surge
To make matters worse, the storm’s presence coincided with astronomically high tides. The NWS’s meteorologist, Jon Palmer, said that the high tides could be record-breaking. He expected the tides could reach 13 feet and even break the 13.24 -foot record that was set at Hampton Beach during the Blizzard of 1978.
Normal tide range in Portland, Maine is 9.1 feet. Boston is 9.5 feet. So these expected record-breaking tide heights of 13 to 13.24 feet would have water about 4 feet about the average higher high water level (mean higher high water, or MHHW).
The astronomically high tide would mean a level about 1.7 feet about the MHHW. The additional 2.3 feet of water height is storm surge-induced. Keep in mind that these levels do not include the wave height that comes crashing on to the beach at the time of high tide.
We will go into much further discussion of tides and storm surges in Part VI.
So, Why Isn’t This Sea Level Rise?
Sea level is independent of storm surges or varying tidal extremes. The tidal stations along the New England coast that are used to measure sea level rise mark the height of the sea level at a consistent point in the tidal cycle. Sea level is therefore independent of any changes in the tidal cycle due to lunar or solar influences.
It is also measured apart from any storm activity that would cause storm surges. In doing so, the tidal station is designed to just measure actual sea level independent of meteorological or celestial influences.
But This Storm Caused Significant Flooding Even Inland from the Coast
The NWS forecasted widespread flooding as streams overtopped their banks throughout the Piscataqua drainage basin. In a broad-brush forecast, the map below shows the regional susceptibility to flooding, even away from the shoreline.
We know from our previous discussion in Part IV that the drainage basin has experienced the effects of urbanization over the past several decades as the Seacoast Region has been developed. This means that the streams and the Piscataqua River are less “resilient” and less capable of absorbing heavy rainfall in the drainage basin. The NWS forecasted that up to 3 inches of rain was expected to fall during Friday, December 23rd.
Our previous discussion also described the streams in the drainage basin becoming “flashier” as the basin becomes urbanized. This means that instead of a more muted peak flood level moving gradually down the streams and Piscataqua River, an observer would expect to see a more pronounced flood peak arriving faster and then dissipating more quickly as the peak moved downstream.
Why Aren’t the Peak Flood Levels Along the Coast Proof of Sea Level Rising?
The astronomically high tides and the storm surge are no more permanent and lasting than a blizzard causing the next ice age. Once the tides receded and the storm passed, the sea level returned to where it was prior to the storms arrival and before the astronomically high tide.
The 1978 record-braking high tides and storm surge at Hampton Beach were damaging, but the sea level did not rise because of it. The same is true with the December 2022 storm.
It is our contention and our possible theory that sea level is governed as much by volcanism and insolation (see Part III) as any build-up in greenhouse gases in the atmosphere. The December 2022 storm’s impact is entirely separate from sea level rising.
