Matt Driscoll

Rising seas and falling land: Tacoma needs to prepare for the impacts of climate change

FILE - In this Dec. 12, 2014, file photo, waves break on the remains of a structure as a house that toppled over the eroding Pacific Ocean shoreline of North Cove, Wash., is shown in the background. A new report released Monday, July 30, 2018, provides the most detailed projections for how fast sea levels are expected to rise along Washington state shorelines over the next decades. (AP Photo/Ted S. Warren, File)
FILE - In this Dec. 12, 2014, file photo, waves break on the remains of a structure as a house that toppled over the eroding Pacific Ocean shoreline of North Cove, Wash., is shown in the background. A new report released Monday, July 30, 2018, provides the most detailed projections for how fast sea levels are expected to rise along Washington state shorelines over the next decades. (AP Photo/Ted S. Warren, File) AP

How much difference can 2 or 3 feet make? Or 6 inches?

When planning for a rise in sea level caused by climate change over the coming decades, researchers say, even a seemingly small increase in absolute sea level will have big implications along Washington’s more than 3,000 miles of coastline.

Roads, homes and vital infrastructure all stand to be affected. One-hundred-year weather events could become 18-year weather events, experts say.

That includes Tacoma, where researchers expect sea level to rise from roughly 1.5 to more than 3 feet by 2100, depending on the level for greenhouse gas emissions over that time.

Meanwhile, under what researchers consider a “high greenhouse gas scenario” — essentially described as the status quo, where emissions continue to increase — sea levels in Olympia are expected to rise between 2 and 3.4 feet.

How can we plan for this future? That’s one reason why a new report from the University of Washington Climate Impacts Group and Washington Sea Grant is so valuable, according to the researchers behind it.

Released on Monday, the report provides a detailed look at the probable rise in sea levels at 171 sites along the coast and Puget Sound. The study utilizes the latest science, including the potential for higher-than-expected sea level rise in the 21st century.

It also takes “geology driven land movement” into account — in layman’s terms, whether the ground is rising or falling.

The result is a comprehensive and exhaustive examination of what Washington’s coastal communities can expect in the coming years.

Previous sea rise assessments have been “too zoomed out to be useful for local communities,” according to Harriet Morgan, a researcher with the UW’s Climate Impacts Group and a co-author of the new report.

“What our projections did is they zoomed in a lot more,” she says. “We drilled down and made projections every 5 to 7 miles along the coast line.”

While previous sea rise assessments might have been good for headlines, if your job is to plan things like where hospitals and fisheries are built or where roads are constructed, it created more questions than answers, Morgan says.

For instance, while land at Neah Bay is expected to rise, because of geographical conditions, land in Tacoma and Seattle is expected to fall.

That complicates things, but it also makes a big difference.

“It actually magnifies (sea level rise),” Morgan explains of the expected vertical land movement in Tacoma, where experts expect a minimal but not inconsequential drop over the next 130 years.

To paint a picture, Morgan likens it to a bathtub.

“If you were in your bathtub, and all of sudden the sides of your bathtub were lowering, the water would go up,” she explains.

“Previous assessments hadn’t considered vertical land movement, which can play a role in Washington state in either counteracting sea level change or exacerbating it,” adds Washington Sea Grant’s Ian Miller, a coastal hazards specialist who co-authored the report.

“We wanted to take absolute sea level projections and then couple them with a vertical land movement assessment at a scale that’s relevant (to local communities),” he says.

According to Morgan and Miller, one of the most useful aspects of the report is its methodology. The study gives local communities a range of possible sea level changes over time, weighted by probability, allowing planners to use this information when making important decisions about the future.

That’s a potentially powerful tool, since the risk a city might be willing to take on when building a hospital is clearly different than what might be acceptable for building a park or public bathroom, Miller says.

“When you’re talking about something that potentially has a large impact, in a coast environment, you sort of want to try to get it as right as possible,” Miller says.

“From the standpoint of thinking about possible impacts of sea level change on coastal communities, it actually tends to lead to pretty nuanced discussion.”

While it’s early, and the trick will be effectively incorporating these projections into future planning, according to Jim Parvey, Tacoma’s chief sustainability officer, the report has the potential to be extremely relevant here.

It might influence the way we plan and protect ecological restoration areas, roadways like Marine View Drive and Ruston Way, and key facilities built along the water, he says.

“It’s a big step in the right direction,” Parvey says of the report. “It allows us to start war-gaming what we might be dealing with in the future a little bit, as we’re putting new infrastructure on line to see how it will be affected 25 or 50 years down the road.”

“When you’re building something for a city, that’s the kind of time frame you’re looking at,” Parvey adds.

“The better we can look into the future, the better we can design it now.”

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