Eyeing Floods of 2050, Seattle Prepares to Hike its Skirt

(Detail from Seattle Public Utilities map)
Deep blue means glug glug glug. (Detail from Seattle Public Utilities map)

Using very conservative assumptions about how much sea level is rising, City of Seattle planners project that within the next 40 years, storm surges and high tides will flood new areas of Seattle. While the sea level is expected to rise six inches, that coupled with an extreme event could raise the water by three to four feet.

Besides buying flood insurance, the City would like to know what citizens would like to do about their disaster scenario.

The City Council’s Mike O’Brien, chair of the council’s Energy & Environment Committee, says last month’s flooding of  Beach Drive in West Seattle is just the latest wake-up call. It’s time to develop a climate change action plan.

“Over the next two months we will hold a series of public forums and host an online survey to gather input from the people of Seattle to help guide the actions the city needs to take,” said O’Brien in a release to the media. “We welcome all ideas and suggestions for actions we should take in the next three years as well as in the long-term. We plan to adopt a bold Climate Action Plan on Earth Day, April 22.”

Council member Jean Godden, who chairs the committee that oversees Seattle utilities, added, “[W]e have work to do to ensure Seattle’s utility infrastructure and assets are prepared for climate change.” Seattle Public Utilities (SPU) has already been working on reducing its greenhouse gas emissions; Seattle, though supplied in most part by hydroelectricity, has in the past relied on coal to fill as-needed demand.

But SPU has also been mapping the parts of Seattle more likely to flood by 2050, from either a rise in sea level or record tides. Post-Hurricane Sandy, utilities in not-so-flood-prone areas are taking a closer look at their vulnerability to extreme events: Are underground transformers really watertight? Are aboveground transformers high enough? It took New York and New Jersey utilities 11 and 13 days, respectively, to restore power to 95 percent of customers following the hurricane.

One thing to remember when looking at the map is this important caveat: “Data provided by Puget Sound LiDAR Consortium indicates a vertical accuracy in the 2001 LiDAR data (NAV88 Datum) in the order of 1 foot. Considering this margin of error, the 6-inch sea level rise estimate may be too fine a gradation to be predictable.” So the light blue for sea level rise (kind of an idiot choice for color, since it’s next to the light blue for water — ed.) isn’t that reliable.

But also consider that the estimates for the rise in sea level come from University of Washington’s 2008 Climate Impacts Group report (pdf) “Sea Level Rise in the Coastal Waters of Washington State” (with figures from National Tidal Datum Epoch 1983-2001). Given the global rate of sea level rise already (Seattle’s trend for the past century has been two millimeters per year), researchers decided that at least six inches by 2050 was most likely — but their worst case scenario was 22 inches.

A 2012 report, “Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future,” using recent satellite data to track an increase in the rate of sea level rise, now projects as much as nine inches by 2030, and 19 by 2050. (This is all contingent upon an 8.0 megathrust quake not submerging us by seven feet, which has happened before. It turns out the Washington coast’s sea level rise is variable because parts — the northwest Olympic Peninsula, for instance — are being pushed up by tectonics faster than the ocean is rising.)

If you’re a fan of Nassim Taleb, you will already know that he advises people to prepare for the worst and let the likely take care of itself. With that in mind, our vulnerability to a Cascadia subduction zone megathrust earthquake far outpaces the risks of sea level rise from climate change. The latest odds are about 37 percent that Seattle will feel an 8.0 or greater in the next 50 years. When that occurs, the tsunami could be catastrophic (see pdf model of tsunami impact). The last megathrust quake, in 1700, sent a tsunami that was 30 feet tall when it hit Japan.