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Originally published Saturday, January 12, 2013 at 9:02 PM

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Seattle calculates how climate change will redraw its shores

Seattle Public Utilities maps the local effects of global climate change and projects that by 2050, higher shorelines will inundate parts of Interbay, Georgetown, South Park, West Seattle, Golden Gardens and Harbor Island.

Seattle Times staff reporter

Seattle confronts a changing world

Climate Action Plan: www.seattle.gov/environment/climate_plan.htm

Green Ribbon Commission Recommendations: www.seattle.gov/environment/documents/GRCReport_forweb.pdf

Source: City of Seattle Office of Sustainability and the Environment

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Parts of Interbay, Georgetown, South Park, West Seattle, Harbor Island and Golden Gardens will be under water as the local shoreline creeps higher due to global climate change, Seattle Public Utilities predicts.

A recent map is just one of many such reckonings in the works as city agencies calculate the local effects of global climate change and how to respond and adapt to protect people and infrastructure.

From preparing for more intense heat to protecting the new downtown sea wall under construction to calculating the number of maintenance holes, pump stations and outfalls that will be under water in the new normal, city agencies are readying for sea-level rise caused by the amount of heat-trapping greenhouse gases, especially carbon dioxide, pumped into the atmosphere by human activities.

Calculations by the Washington Climate Impacts Group and the Washington Department of Ecology published in 2008 predict a sea-level rise in Seattle of 6 inches by 2050.

Less-likely scenarios are a sea-level rise of 3 inches on the low end and 22 inches on the high end. And that's the new normal. Winter rain and wind storms and seasonal high tides — or combinations of any of those or other events — mean even higher water.

As part of its ongoing response to climate change, the city of Seattle last year requested an update to its climate action plan from a green-ribbon commission. Its 150 recommendations will go out for a six-week public-comment period beginning Monday.

Agencies also are looking ahead. Climate change is now one more factor engineers and planners must consider as they build projects in Seattle and maintain what's already here.

"We did this map to understand impacts on our infrastructure," said Paul Fleming, manager of climate and sustainability for Seattle Public Utilities (SPU). "In the big picture, this isn't just about sea-level rise. It's about drinking water, urban flooding, and how we design new projects."

The utility is still analyzing the implications of its map, Fleming said. "We did this to understand which of our assets would be inundated under these scenarios. We go from a global phenomenon to something with a much more local flavor: Here are the assets that are going to be wet."

Globally, much of the projected sea-level rise is due to thermal expansion. The ocean is warming and will continue to do so, and that means the water in it is taking up more space. So sea levels rise.

Not everywhere. In some locations, other forces of nature, such as rising landforms, cancel out sea-level rise. The northwest corner of Washington state is still rising from the decompression of the landscape caused by the weight of glacial ice. Collision of tectonic plates offshore is also giving Washington's outer coast a lift — at least until the next earthquake.

Seattle has some things going for it, too. The water supply is in the central Cascade Mountains, so it won't be infiltrated by seawater creeping toward groundwater. But depending on location, water supply, drainage and wastewater infrastructure possibly could be affected by everything from flooding to corrosion as the sea creeps upward.

The system also works largely by hydraulic head, which will be reduced as sea levels rise, reducing the capacity of everything that runs on gravity.

"There are thousands of maintenance holes, and in some, water would go up the pipe instead of down, and if the system is full, it will pop up another (maintenance hole) upstream, spilling onto the street," said James Rufo-Hill, meteorologist for SPU. "It will stress the ability of the system to perform because we will lose pressure."

Other effects of climate change, including drought and wildfires, also could diminish the water-supply quality and quantity in the far future.

The results of sea-level rise will remain hard to predict, in part because sea level is linked to so many factors. "The bottom line is, you can come up with a variety of numbers for one location, but the real question is one of timing," said Phil Mote, lead author of the 2008 sea-level rise report and scientist at the Oregon Climate Change Research Institute.

"When is the next huge storm going to coincide with a high tide in winter and an El Niño? We don't know when that bad timing of factors is going to lead to inundation; it could be next winter, or 50 years from now."

But some degree of sea-level rise is certain, Mote said. "It's basic physics. Ocean water heats, and it expands. You just can't get away from rising sea levels being an inevitable consequence. How much and how fast: That alone is what determines how the shorelines will look."

Meanwhile, the climate continues to warm. According to NOAA's Climate Data Center, 2012 was one for the record books in terms of temperature and extreme weather events, from drought to wildfires, hurricanes and storms.

Last year also saw a record warm spring, the second-warmest summer, fourth-warmest winter and a warmer-than-average autumn. The average temperature for 2012 was a full degree above 1998, the previous warmest year ever, and 3.2 degrees above the 20th-century average.

Seattle City Councilmember Mike O'Brien said that while city officials may feud on some issues, they are united in recognizing the importance of global climate change. From tolling to discourage driving to energy efficiencies in heating and cooling buildings, there is a lot the city needs to look at to respond with prevention and adaptation strategies, O'Brien said.

Denis Hayes, president and CEO of Seattle's Bullitt Foundation, and co-chairman of the green-ribbon commission, noted that with the feds in limbo, it will be up to the locals to innovate and imagine solutions, despite the global scale of the problem.

"You are helping to transform the culture, and you can have things that come up from the grass roots rather than being dictated from above that will endure and benefit future generations," Hayes said.

"What can we do that is bold and will capture people's attention? If we do it well and succeed in Seattle, others will notice."

Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com. On Twitter @lyndavmapes.

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