Study: 17,500 NW Homes In Harm's Way From Rising Seas

Mar 16, 2012

Seventeen and a half thousand. That's how many Oregon and Washington homes could be inundated by rising seas caused by global warming over the next century. The number comes out a study by the research non-profit Climate Central and the University of Arizona.

Right now, the level the Pacific Ocean rises about three millimeters per year. But research is one thing... taking action is another matter.

The study authors calculated how many Americans live less than 1 meter above the high tide line. In Washington state, that's about 10,500 homes, plus another ,7000 in Oregon that could be flooded by rising seas.

The biggest concentrations of vulnerable homes are in Seattle, and Warrenton and Seaside, Oregon. In a storm surge, rising seas could even affect the lower Columbia River including Longview and parts of Portland.

Nate Mantua is co-director of the Climate Impacts Group at the University of Washington. He wasn't directly involved in this study, but he says what's new here is the novel combination of high resolution elevation, population and tidal datasets.

"They didn't actually consider any specific future sea level rise scenario," Mantua explains. "Instead, they are using a one-meter increase as a reference and asking how many people would be vulnerable to a one-meter sea level rise. They didn't actually say that's our scenario for 2100."

Other studies have calculated how high the sea could rise locally due to melting glaciers, disappearing ice caps and the simple expansion in the volume of water as it gets warmer. Three feet, or one meter, is on the high side of the range for the end of this century.

But Mantua points out there is a great deal of local variation to consider. For starters, the land you live on is not staying still.

"Different parts of the coast are moving up and down at different rates over pretty short distances in the Northwest," Mantua says.

Here in our region there are numerous examples of cities and states that have completed assessments for how vulnerable they are to rising sea levels. The Swinomish Indian Reservation, City of Seattle and the State of Washington's highway department to name three.

But examples of places that have taken some concrete action in response are much harder to find. In Aberdeen, Washington, public works director Larry Bledsoe thought up an affordable defense. He's recommending the city council progressively raise the minimum elevation of ground floors in new construction.

"It seems prudent to make small adjustments now incrementally before the flood is upon us," Bledsoe says.

Another example from western Washington: A couple years ago, Nisqually Wildlife Refuge managers considered rising sea levels when they designed new dikes to protect freshwater wetlands. The new dikes have an extra wide base so they can more easily be built higher in coming decades.

"There is a little time if you want to put it that way," says John Clague. He's an expert on sea level change at Simon Fraser University near Vancouver, BC. Low-lying suburbs there are taking a hard look at their strategies.

"It's a bit like the options open to the military during a war," Clague says. "We can defend or we can retreat. Both are not very palatable options."

He says holding back the waters or relocating structures inland are both "very, very costly."

"Where the money is going to come from, I don't think anyone knows because it's a large amount of money. You know, it's outside the ability I think of most communities to deal with this problem, most urban communities in coastal areas."

Clague is worried by signs that indicate sea level rise is accelerating. His home province of British Columbia is telling its local jurisdictions to prepare for an average increase of about one meter over the next century.

On the Web extras:

This is the research paper as it appeared Wednesday in Environmental Research Letters:

Surging Seas: Climate Central report:

Province of British Columbia:

The UW Climate Impacts Group projected mean sea level rise to 2050 and 2100.
Puget Sound 2050: 6" (range 3"-22")
Puget Sound 2100: 13" (6"-50")

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