John’s Blog/Newsletter: SEA LEVEL RISE NOW

“Do I have 20 or 30 years before my property floods?” is a typical question I get at least once a week. The other day it was someone about a property in Ochlockee Bay, marked on the map, an hour’s drive south of Tallahassee in the Florida panhandle.  Before that the request was about the Bahamas; prior to that, Prince Edward Island, Canada. Though I’ve written about this before, it’s worth revisiting and clarifying. Flooded streets, homes and businesses are becoming more and more common in coastal communities all over the world. Increasingly, people are realizing the reality of sea level rise (SLR) but have no sense of how soon and how high.  In fact, the question is very complex. Let’s look at 4 issues that need to be considered to get the answer they seek.

#1 – Recognize that flooding can combine 5 kinds of flood factors:

• (1) Storms, with hurricanes (typhoons) being extreme examples
• (2) Heavy rain, due to the warmer oceans, evaporating more moisture into the atmosphere
• (3) Downhill and downstream runoff, are related to heavy rain, but can multiply the water depth many times the rainfall, and move the flood hundreds of miles.
• (4) Extreme tides, following the cycles of the sun and moon, from monthly to a little-known 19-year pattern.
• (5) Rising sea level, the long-term game-changer.

Property near the coast has increased vulnerability to storm waves, but even if it is considerably inland, very low-lying property can flood from rising sea level by means of waterways, marshlands and tidal rivers. For example Sacramento, California is 80 miles from the coast, but is on a tidal river and vulnerable to sea level rise. Another special circumstance is if the property is built on porous rock, as is the case in South Florida and most coral-based islands. Porous limestone allows flooding to come up through the ground, even if it’s miles from shoreline. Headline disaster stories from the US Midwest, to India, China, make clear that the combination of the five flood factors can be catastrophic. You need to consider the risks of all five factors for your location.

#2 – Look at your property’s vulnerability in terms of lowest opening in the structure (doors, windows, vents). Equally important, consider the flood vulnerability in terms of your neighborhood and wider community. Will the streets and emergency access flood even before your property? What about power supply, fresh water supply, waste water, and communications? All of those factors will not only determine your safety and vulnerability, they will affect the value of your property. It’s great if you have the highest elevation of all your neighbors, but what if you wind up effectively on an island?

#3 – Understand sea level rise. It cannot be stopped this century, though it can be slowed if the world very aggressively works to slow the warming. Since we do not know how effective the world is going to be in terms of slowing the warming, we cannot precisely predict the height of future sea level, which largely comes from the melting ice sheets and glaciers. From what we know at present, safe planning is perhaps for a foot of higher base sea level by mid-century, only a few decades from now.

By mid-century the acceleration of sea level rise could “kick into high gear” at an exponential rate as I explained in a previous blog post. The second half of this century could bring six feet or more of sea level rise (SLR) which would be catastrophic. Even just a couple of inches of higher sea level, added to storm water heights, could be all that’s needed to breach a levee or threshold. Even one foot of higher sea level will be incredibly damaging to coastal communities. Infrastructure, businesses, and homes will take a big hit with more and more flooding at extreme high tides. Damages will be in the billions. An unknown is how soon will forecasting models be able to accurately predict the acceleration of SLR, which in part depends on our energy policy and technologic advancements to slow the warming. Better clarity about the future will affect current values. Also, SLR is not the same everywhere. In areas of land subsidence such as New Orleans (Louisiana), Hampton Roads (Virginia), Venice (Italy) and Jakarta (Indonesia) sea level rise is much faster and higher than the global average.

#4 – Market forces and psychology could discount values surprisingly soon. The above three points describe how your property will be affected physically by rising sea level combined with other flooding. The value of your property is determined by another factor: Market perception of value and risk. Even if your house has never flooded, but the flood waters from extreme high tides and storms are getting closer to your property, the value will likely be affected. Just as in the stock market, there is a saying that markets discount for future risk. In some areas with frequent flooding, property values already are being reduced.

I tell people there are 3 ways your house can go underwater: a) Permanently, when it is fully submerged by sea level rise. b) When it floods more frequently due to the combination of flood factors. Buyers might tolerate a rare flood event, but frequent flooding from any source, dilutes property values dramatically––who wants to buy a property that floods even a few days a year. c) The value can go “underwater” even before the water reaches the property line, if it becomes clear that the water is moving ever-closer.

I tell people that a decision about when to sell and when to move depends on your age, risk tolerance, your concern about the value of your estate, etc. Changes to federal and insurance industry policy could also substantially change the cost of flood insurance. It has been estimated that a $500 change in annual insurance premiums can change the property value by ten thousand dollars.

The fact is that there is no way to precisely say how many years you have with any particular piece of property. The above points may give you a better idea of the variables and the nuance. This new era of warmer temperature, producing extreme rainfall events, stronger storms and accelerating sea level rise is changing our world in real-time. When the accelerating rate of sea level rise becomes more obvious, vulnerable coastal property values could decline a lot faster than anyone imagines.

We are in uncharted territory…terra incognita as they used to say, the term for uncharted lands and treacherous sailing. As weather patterns change and sea level rises higher and faster than at any time in recorded human civilization, we too must navigate in uncharted territory.