New Puget Sound climate study: Older projections coming true, more changes ahead

Closer to home than the thousands of world leaders in Paris to discuss how to limit the scale of human-caused global warming, the consequences of climate change underway around Puget Sound have been detailed in an in-depth scientific study.

The report, issued in November by the University of Washington’s Climate Impacts Group, found projections in a 2005 study on potential warming effects have come to pass, its authors said. The consequences threaten cornerstones of South Sound life from worsening floods and droughts to diminishing salmon stocks and snowpacks.

Possible consequences include changes to lifestyles perhaps difficult for previous generations to conceive. Consider: a mostly snowless Mount Rainier looming over a population so battered by intense rainstorms that umbrellas come into regular use, even by Puget Sound lifers.

In the near term, however, climate change for Puget Sound is not projected to be as cataclysmic as in regions already facing livability challenges. Ocean rise isn’t on pace to subsume entire islands here. Temperatures are not approaching Saharan levels. The average annual precipitation is even expected to remain about the same.

“The good news part of the story is that certainly, relative to other parts of the world, the Pacific Northwest is somewhat insulated from the most extreme effects,” said Joel Baker, science director at the Center for Urban Waters.

But the way South Sound cities and towns have developed around predictable slow rains and summer snow melts has begun to show signs of strain, which the study’s authors say are expected to worsen.

“If anything, some of the projections were low,” Baker said. “We’re seeing more changes than even they projected in 2005.”

HIGH-INTENSITY STORMS CAUSING FLOODING

The study found that a higher percentage of the the region’s annual precipitation is arriving in short, high-intensity storms, which dump water faster than drainage systems were built to handle.

Tacoma streets crews are installing new stormwater catch-basins through the Stadium District to combat recurrent flooding problems in historic Stadium Bowl.

“The heaviest 24-hour rain events in the Pacific Northwest will intensify by 19 percent, on average, by the 2080s,” the study states.

Flooding isn’t just a municipal-infrastructure problem, said Guillaume Mauger, the study’s lead author.

The melt of glaciers off the side of a volcano, such as Mount Rainier, carries high amounts of sediment into streams and rivers, which when it accumulates on the river bottom “could really create more flooding downstream,” Mauger said.

A federal study of the White River after flooding in Pacific in 2009 found that sediment buildup had cut some river channel capacity 20 to 50 percent, pushing the waters up and out of the established banks.

“In some places, sediment on the river bottom was 10 feet higher than it used to be,” Mauger said.

Sea-level rise — not a direct threat to most of the South Sound, though low-lying downtown Olympia is a notable exception — also is projected to worsen river flooding by making it harder for swollen rivers to drain into the Sound.

DEMAND ON RESERVOIRS COULD CLIMB

Because higher temperatures are projected to hasten snowmelt and make more of the region’s precipitation fall as rain, water systems that depend on melting snow to fill the watersheds they draw from could be forced to turn more to the prospect of increasing reservoir use.

“That’s expensive, and the environmental impact is a whole can of worms,” Baker said, “but the fact that the annual precipitation (amount) is not changing means to me that we’re not going to run out of water. We’re just going to have to build systems that kind of replace a snowpack.”

One example of that is planned near Sequim, where the Washington Water Trust is aiding an effort to build an 88-acre reservoir on state-owned land to be fed by seasonal high flows of the Dungeness River. Its estimated cost is up to $32 million, for which state money has not been appropriated.

State Department of Ecology officials said they aren’t familiar with any recently built reservoirs.

“To dig a new reservoir is a huge and costly undertaking,” Ecology Department spokesman Dan Partridge wrote in an email.

The three largest Puget Sound municipal water suppliers — Seattle, Tacoma and Everett — each depend on a system of reservoirs and groundwater wells that has not shown significant strain in recent droughts.

Using the low and moderate greenhouse-gas scenarios for coming decades, the study projects Tacoma’s water supply, will in 2070 to 2099 be about 93 to 96 percent of what it was from 1970 to 1999.

The study’s projections do not account for any change in demand for municipal water supplies, from population or industry. A proposed methanol plant for the Port of Tacoma would require up to 14.4 million gallons a day, which equates to about two-thirds of all the water used by Tacoma Water’s residential customers in 2014.

Tacoma Public Utilities spokeswoman Nora Doyle said Tacoma would rather expand resources, such as developing more water-storage capacity behind Howard Hanson Dam on the Green River, than look into excavating a new reservoir.

“Storage is an important issue, especially if we regularly see warmer, drier summers and falls with less snow and rain, or if we see considerable growth in the region,” Doyle wrote in an email.

Although the climate change study focuses on environment and not demographics, Baker said population growth throughout the Puget Sound region could be boosted further with climate-change refugees from areas facing more extreme impacts, including the southwestern United States and Southeast Asia.

“Where those people go is a really complex, important question,” Baker said, “and I don’t think anyone knows the answer to that.”

SALMON PRESSURED TO ADAPT

Because less precipitation will be arriving as winter mountain snow, less snowmelt will feed streams juvenile and spawning salmon rely on in summer. The study says thermal stress and other new problems could harm salmon and steelhead populations faster than they can find new places to migrate.

“Their life cycle depends on having the right amount of water coming down the rivers at the right temperature at the right time,” Baker said. “If they don’t have that, then they’re not going to survive.”

As summer streams warm and shrink, the fish populations that do find safe waters will be packed closer together, making them more susceptible to disease, the study says, though the diversity of salmon in the region might help the fish’s resiliency rate.

Other fish, too, would feel consequences from warming waters, including lake species. Warmer waters can give those habitats spring plankton bloom earlier than the next link up in the food chain — a type of water flea — is ready to consume them, destabilizing the system’s balance.

Taken as a whole, Baker said, the study shows climate change is bringing “a fundamental shift in the way the Pacific Northwest system works” and will require many adaptations.

“It goes well beyond not being able to ski as much as we’d like,” he said, “as much as we’d like to think that’s the most important part of it.”

This story was originally published December 2, 2015 at 11:37 AM with the headline "New Puget Sound climate study: Older projections coming true, more changes ahead."