Global Warming
12:23 pm
Fri March 16, 2012

Study: 17,500 NW homes may sink under rising seas

Thousands of homes in Washington and Oregon could be inundated by rising seas caused by global warming over the next century, according to research by the non-profit Climate Central and the University of Arizona.

By calculating how many Americans live less than 1 meter above the high tide line, the researchers found 10,500 homes in Washington and 7000 in Oregon that would be flooded by rising seas.

The biggest concentrations of vulnerable homes are in Seattle, and Warrenton and Seaside, Ore.

In a storm surge, rising seas could even affect the lower Columbia River including Longview and parts of Portland.

Unique study

Nate Mantua is co-director of the Climate Impacts Group at the University of Washington. He wasn't directly involved in this study. He's 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. 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," Mantua said.

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," he said.

Projections

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")

Raise the floors

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, Wash., 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 said.

Time to prepare

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," said John Clague, an expert on sea level change at Simon Fraser University near Vancouver, BC. "It's a bit like the options open to the military during a war. We can defend or we can retreat. Both are not very palatable options."

... and both are 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 1 meter over the next century.

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