‘Riley’ Reinforces 5 Forms of Flooding
“Riley” was the 2nd Powerful Nor’easter to bash Boston in 2 Months; Severe Flooding. (NASA)
“Riley” was another deadly “100 year storm” that hit New England Friday (March 2nd). The previous “100 year storm” with even more fatalities hit the same area exactly 2 months earlier. That was “Grayson” but was better known as the “Bomb-cyclone” to describe its explosive rate of growth. Welcome to the age when unusual becomes the usual.
Looking at the issue of flooding, what are the lessons to be learned? Clearly statistics, and terms like a “100 year event” are now probably more misleading than informative.
If we are going to see the new reality in front of us and prepare for the future, we need to identify the different flooding components. Each is quite unique in terms of how predictable it is, how high it can get, and how long it will last before it recedes. Here are my five flood factors – with notes about how Riley demonstrated each.
- Storms – the weather system, possibly a hurricane, that tears at the coast with waves and storm surge. Riley packed wind speeds up to 70 mph (110 km/h) with some reports over 90 mph. The waves were estimated to be the height of a two story building, and put boulders on the streets of coastal towns like Scituate. That water quickly recedes.
- Rainfall (or snow) – this system dumped almost 40 inches (100 cm) of snow and 6 inches (15 cm) of rain along its path
- Runoff – it’s too early to calculate the runoff as the snow melts, and the rain moves downhill. While it is related to the precipitation, depending on topography it could multiply rainfall ten times deeper – or more
- High Tides – Last Friday was the highest tide EVER RECORDED in Boston Harbor, 14.7 feet (4.5 m) This was due to the three foot storm surge hitting at the monthly “full moon” high tide, in a month with a strong “king tide.” (For explanation of king tide see my blog post from two weeks ago.) The storm surge added a little over three feet to the king tide.
- Sea level rise – Over the last century, sea level in Boston is about a foot higher (30 cm), both due to the global higher sea level and some changes in ocean currents. Sea level rises much slow than all the other weather related flood effects. But sea level rise will not recede for millennia. It effectively raises the baseline for the other four causes of short-lived flood events.
Flooding is the combination of all five of these factors. When we recognize that higher sea level changes the baseline, we can more clearly see the challenge to design and build flood resistant communities.
So if I were planning future infrastructure or buildings in areas that need to rebuild following Riley, taking into consideration the 5 flood factors I would allow for three feet of higher sea level if I wanted to design for fifty years, and eight feet of higher sea level if I wanted the structure to be safe for one hundred years. That may seem extreme, but the facts about ice sheets and glaciers melting faster and faster are quite clear.
Living and dealing with strange storms, worse wildfires, record heat, deadly droughts, and severe snowfall is becoming the new normal. Why? Because the oceans have absorbed a tremendous amount of extra heat over the last century, enough so that average global ocean temperatures have warmed about 1.5 degrees Fahrenheit (one degree Celsius) over the last century. That is huge. 93% of the extra heat that is trapped by the insulating greenhouse gases is stored in the sea. To give you an idea of the extraordinary amount of this added heat…
we are raising ocean temperature, with the additional heat energy of four atomic bombs, every second, 24 / 7
Warmer oceans change ocean currents, thaw the Arctic Ocean, and change atmospheric currents like the Jet Stream. After 11,000 years of climate stability (holocene) we are in a new era (anthropocene). Now, we can see things are different and we know why. It’s that extra heat stored in the sea.
Could a “Riley” happen again? Without question. Like all variable weather it is hard to say when, where, and how strong beyond the current forecast technology of a few weeks. What we can say for sure is that we have de-stabilized weather patterns and climate, and that sea level will be higher, eventually many feet higher.
The latest estimates for sea level rise, are for a foot or two by mid century–just a few decades from now, and possibly six to eight feet by the end of the century. (Exactly how much depends on how warm we let the planet get between now and then.)
Next week, I will share my new message, “Why We Must Rise with the Tide”, as a call to begin seeing the future risk, as a challenge and opportunity.