Photo: Lindsay/Flickr for the WA King Tide Photo Initiative

Sea Level Rise and I-1631: What’s at stake for Washington?

, senior climate scientist | October 29, 2018, 1:53 pm EST
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On November 6th, residents of Washington will be casting their votes on Washington Initiative 1631, also known as the Protect Washington Act. If I-1631 passes, Washington will become the first state in the nation to directly put a price on carbon. The funds raised through I-1631 would be used to promote a cleaner, healthier environment for Washington residents.

While the recent intense wildfire seasons have understandably received a lot of attention, Washington is also at risk from a more insidious, ongoing threat: sea level rise. In the coming decades, sea level rise could put thousands of homes in Washington at risk of chronic flooding, which is flooding that happens 26 or more times per year.

Washington faces a range of climate risks that I-1631 could help to minimize, and Washington’s scientists agree that it’s time to act to minimize these risks (see the UCS-supported letter signed by 200 scientists calling for I-1631 in the Seattle Times). Let’s take a look specifically at the potential impacts of sea level rise and chronic flooding in Washington and how I-1631 could help.

How much has sea level risen in Washington so far?

There are six NOAA-maintained tide gauges that measure water levels along the coast of Washington. The state’s longest-operating gauge is in Seattle and has been in place since 1899. Since then, the gauge has measured an average rise in sea level of roughly 2.1 millimeters per year, for a total rise of about eight inches over the last century. That’s roughly on pace with the global average rise in sea level.

The Seattle tide gauge has measured an average rise of 2.05 mm/year since the turn of the 20th century. Other gauges in the state, brought online in the 1970s, record a slower rise.

Gauges installed in the 1970s at other points along the coast–such as Cherry Point, near the Canadian border, and Port Angeles–have recorded a notably slower trend of roughly 0.4 mm per year. This difference reflects the fact that some parts of the Washington coast are subsiding–such as those in the Seattle area–and some parts are undergoing uplift.

These rising and falling trends on land reflect the region’s tectonic patterns as well as processes such as the compaction of sediments and groundwater withdrawal, which can cause the land to sink. So the pace of local sea level rise is highly variable around the state.

The pace of local sea level rise varies considerably in Washington because some parts of the state are experiencing land subsidence while others are experiencing uplift.

And how much will sea level rise in Washington in the future?

Because of the differing land movement trends in Washington, projections for how much sea level will rise in the coming decades also vary. The state’s most recent sea level rise guidance includes site-specific projections for more than 170 locations along the coast, which is more detailed than anything I’ve seen for any other state in the country. The state reports both a likely range for the amount of sea level rise over time and higher magnitude but less likely possibilities that bracket an upper limit given the latest science.

The state’s guidance gives a likely range of 0.5 to 0.9 feet of sea level rise for the state as a whole by 2050, and states that there’s a small chance the state could see up to 2.0 feet in that timeframe. By 2100 given a high emissions scenario, the likely range of sea level rise for the state is 1.4 to 2.8 feet by 2100, though could be as high as 8.3 feet.

In our recent work on the extent of chronic flooding and its impacts on coastal real estate, we used a set of sea level rise projections based on those developed for the third National Climate Assessment and adjusted to account for the different rates of land movement as measured at the tide gauges around the state. We found that, with a high sea level rise scenario, the state could see an average of 1.9 feet of rise by 2050 and 6.2 feet by 2100. With a low scenario, in which emissions are drastically reduced and future sea level rise is limited, our projections show an increase of 0.5 feet by 2050 and 1.3 feet by 2100.

It’s important to note that our projections use a sea level baseline of the year 1992 while the state’s projections use the average sea level over the period from 1991-2009 as a baseline. Overall, the projections we used for our high scenario fall within the mid- to upper range of the state’s projections. And our low scenario falls below or at the lower end of the state’s stated likely range.

How will sea level rise impact Washington?

A king tide spills over a roadway in Harper, Washington in November 2014.

During above-average high tides or king tides today, impacts on the Washington coast are fairly minor, though high tides can affect access to parking lots, beaches, and other recreational areas.  As sea level rises, however, those high tides will become higher and reach farther inland.

Our analysis shows that by 2045, with our high sea level rise scenario, more than 7,000 homes statewide are at risk of chronic flooding. Nearly half of those are in the Aberdeen-Hoquiam region along Greys Harbor and the Chehalis River.

By 2045, with a high sea level rise scenario, roughly 3,200 homes in Aberdeen and Hoquiam are are risk of chronic inundation.
To explore areas at risk, see our When Rising Seas Hit Home mapping tool.

By the end of the century with that same high scenario, more than 23,600 homes statewide are at risk, including nearly 40 percent of those in the Aberdeen-Hoquiam region and 30 percent of those on the Lummi Reservation, located north of Seattle close to Bellingham. You can explore the number of homes at risk, along with their present day value and other data, using our interactive mapping tool for the state as a whole as well as by community and by ZIP code.

What does Washington have to gain by passing I-1631?

The passage of I-1631 in Washington and the emissions reductions that would result may seem like a drop in the bucket of what’s needed on a global scale. And indeed, limiting future warming will require concerted effort at every level from the individual to the international. But were the world to follow Washington’s example and substantially reduce emissions, there’s a possibility that future sea level rise could be limited.

The low sea level rise scenario we analyzed is predicated on a climate future in which global warming is limited to less than 2 °C above pre-industrial levels. This scenario highlights just how much Washington stands to gain: Compared to the high scenario, in which more than 23,000 homes are at risk of chronic flooding by the end of the century, there are only about 7,000 homes at risk statewide given the low scenario. In other words, roughly 70 percent of the homes that are potentially at risk could avoid chronic flooding were we to achieve this low scenario.

While the emissions choices we make today have a strong bearing on where we land at the end of the century, our past emissions have locked us in to a certain amount of sea level rise in the near term. With that in mind, we need to be helping coastal communities build resilience to the sea level rise-induced flooding they’ll likely see in the next few decades.

And that’s where I-1631 really shines: The funds raised through the initiative could be used for projects that limit community-level harms due to sea level rise. For example, the measure states that “Investments from this account may be used for…relocating communities on tribal lands that are impacted by flooding and sea level rise.” The Affiliated Tribes of Northwest Indians, which includes the Lummi Indian Nation, have supported the initiative.

And twenty-five percent of the revenue would go to a “clean water and healthy forests account” that would include projects that “reduce flood risks and prepare for a rise in sea level.” This forward-thinking approach is one that could be a model for other states to follow.

From a sea level rise standpoint, The Protect Washington Act is a clear winner for the state of Washington.

Photo: Lindsay/Flickr for the WA King Tide Photo Initiative
NOAA Tides and Currents
Miller et al. 2018
Photo: Fletcher Sandbeck/flickr

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