UW News

February 8, 2019

‘Underwater forecast’ predicts temperature, acidity and more in Puget Sound

UW News

Most of us rely on the weather forecast to choose our outfit or make outdoor plans for the weekend. But conditions underwater can also be useful to know in advance, especially if you’re an oyster farmer, a fisher or even a recreational diver.

A new University of Washington computer model can predict conditions in Puget Sound and off the coast of Washington three days into the future. LiveOcean, completed this past summer, uses marine currents, river discharges and weather above the water to create the forecasts.

“It’s like a weather forecast of the ocean in our region,” said lead developer Parker MacCready, a UW professor of oceanography. The project is the culmination of about 15 years of work. “It started off small, modeling parts of Puget Sound, and went to modeling the Columbia River and the coastal ocean nearby, to modeling the whole region. We’re making the model bigger and more realistic all the time.”

Unlike existing marine forecasts that tell boaters the wind and waves out on the water, this model drops below the water’s surface to predict water temperature, salinity, oxygen, nitrogen, pH, chlorophyll — a sign of biological productivity — and aragonite saturation, the most important factor in shell formation, from the surface down to the seafloor.

The simulations are updated daily on the UW’s Hyak supercomputer with a resolution of 500 meters (about a third of a mile) throughout Puget Sound, and slightly more for the outer coast, from southern Oregon to near the tip of Vancouver Island. The model incorporates 45 river flows, uses a UW weather forecast for wind, rain and sunlight, and compares its predictions against dozens of marine testing sites.

LiveOcean was originally developed to predict the impacts of more acidic seawater on the local shellfish industry, and has support from the state-funded Washington Ocean Acidification Center as a tool for local shellfish growers. This will be the first spring that the tool is available for their use.

“If growers buy seed from a hatchery, when’s a good time to put those out in the water?” MacCready said. “Is there predicted to be a very corrosive ocean acidification event? If so, they should hold off until the water becomes less acidified.”

The National Oceanic and Atmospheric Administration also funds the project. It uses the forecast in combination with human analysis to produce the joint UW-NOAA bulletin on harmful algal bloom forecasts, or “red tides,” that it shares with coastal managers.

The Puget Sound forecasts have other applications. Elizabeth Brasseale, a UW graduate student in oceanography, has used LiveOcean to predict where invasive green crab larvae might travel next, enabling Washington Sea Grant to pinpoint its green crab eradication efforts. The model can predict the three-day drift path for any object — spilled oil, wastewater overflow, trash or even an old-fashioned message in a bottle — released from a given point in Puget Sound.

The LiveOcean forecasts are now available on the UW-based Northwest Association of Networked Ocean Observing Systems website. To access the forecasts, click “Layers” at the top left, find “Models” and then scroll down to “LiveOcean” to view maps for temperature, salinity, oxygen, nitrogen, phytoplankton, pH as well as aragonite saturation. (Click the scale bar to make it bigger.)

LiveOcean is among a handful of seawater forecasts being developed for the Pacific Northwest. The SeaCast app, from Oregon State University, covers Oregon and Washington coasts. The SalishSeaCast from the University of British Columbia focuses on the Salish Sea, and the Salish Sea Model from the Pacific Northwest National Laboratory simulates the region’s water but does not issue forecasts.

MacCready compares the situation with global climate models, where models with different specialties give a better overall understanding of the system.

While the daily LiveOcean forecast is useful for making decisions today, the tool also has accumulated several years of historical simulations that allow people to analyze past events, like the unusually warm conditions off the Pacific Northwest coast that peaked in 2015.

“We know that our model is able to reproduce ‘the blob,’ and that it shows up really nicely,” MacCready said. “This new version will allow a much better exploration of what that event looked like inside the Salish Sea.”

LiveOcean builds on decades of experience with Puget Sound’s complex geography and intricate coastlines. In addition to helping managers, it’s intended to act as a teaching tool. MacCready has created documents on how tides work in Puget Sound, the long-term warming trend in Puget Sound and has written an accompanying primer on where Puget Sound’s water comes from.

“The big thing I try to explain to people is that we have this persistent current below the surface dragging deep, saline water into the Salish Sea, where it mixes with the freshwater and then flows out,” MacCready said. “That flow is 20 times bigger than all our rivers combined, and it brings in 95 percent of our nutrients. It’s really the biggest river in Puget Sound, but it’s actually coming uphill, from the deep ocean.”

As spring arrives in Puget Sound, the rains will let up, snow will melt and the rivers will begin to rise. Winds along the coast will soon reverse direction, which draws more nutrient-rich flow from the deep ocean. And residents of the Sound will be getting out on the water for activities of all kinds.

“Now that this makes daily forecasts and performs pretty well, I think it could be used for a lot more applications,” MacCready said. “I’d be delighted to hear from people with ideas.”


For more information, contact MacCready at 206-685-9588 or pmacc@uw.edu.