A new report offers an updated look at flooding risk on the Skagit River, where some of the most damaging floods are expected to become more frequent with climate warming, while existing infrastructure such as dams and levees won’t be able to protect communities from the worst of it.

The project, led by the Swinomish Indian Tribal Community, with partners including the University of Washington Climate Impacts Group, is intended to help local leaders and residents better understand their risk. They hope the flood model they developed can inform emergency management and development decisions, and help the region adapt, said Heather Spore, environmental policy manager with the Swinomish tribe. 

The official federal flood maps in Skagit County haven’t been updated since 1985. When the group started the project, they heard from local officials still relying on paper maps from the Federal Emergency Management Agency. Then a December deluge brought record flooding to the region. About 75,000 Skagit Valley residents were ordered to evacuate. 

The model was nearly complete by the flood, and the group was able to provide some animations of the 100-year flood to Skagit County emergency managers during their response.

“And even though you have an overarching assumption, or you know that it’s going to get worse over time with climate change, you may not have a real picture in your mind of what that looks like,” Spore said. “We didn’t have a good way to visualize that or understand how that impacts people’s ability to shelter in place or evacuate from certain locations.”

The model was used to produce a series of maps that show the depth and duration of river and coastal flooding across specific locations, including hazards to people and cars. They include flooding projections for the 2040s and 2080s. The maps also show the potential for dike failure at specific locations, informed by an earlier federal project. 

Even if the broad contours are similar to the old maps, the details are different. Specific places, like the town of Hamilton, get hit really hard at almost every flood level. And that’ll happen even more in the future. Parts of Sedro-Woolley will remain dry and could provide refuge.

The maps can help residents better understand what roads will be flooded and unsafe, as well as risks to their homes and businesses. The project team built from an Army Corps of Engineers model, incorporating the most up-to-date projections on Skagit River and coastal flooding, as well as on the Samish River. It’s not a regulatory tool and nobody will be compelled to use it, Spore said. But the report, maps and additional materials are all available and free to access online. 

“We’re hoping that this information can really be helpful to local jurisdictions and the community who look at these maps and say, ‘Oh, wow, we better have a go-bag. We better have an alternate route,’” Spore said. 

Floods have long been a fact of life along the Skagit River, the largest watershed draining to Puget Sound. 

The Skagit, like other Northwest rivers, used to move in broad, slow pulses amid heavy rainfall. Water could fan out over a wide floodplain — through oxbows, sloughs and braided channels. European settlers evicted the river, confining it to a narrow channel, while building their lives and livelihoods in the floodplain. 

Now, flooding puts more than half of Skagit County’s more than 130,000 residents in harm’s way, also threatening businesses and salmon. 

Human-caused climate warming will continue to fuel a shift from snow to rain in the mountains that feed the Skagit watershed. Instead of being held in natural storage and slowly melting off in the spring, more precipitation will fall as rain and course into the river to fuel bigger floods. The Northwest has seen about a 25% decline in peak snowpack since 1950, and modeling suggests that by the 2080s, snowpack could be at about less than half of historical levels. 

All of the effects of climate change — including heavier rainfall, rising sea levels and increased sediment flowing downstream — point toward larger floods, said Guillaume Mauger, the state climatologist and a research scientist at the University of Washington Climate Impacts Group.

On average, climate models project that the heaviest storms will become about 22% more intense by the 2080s on average, and Skagit, Padilla and Samish bays are projected to see 1.5 to 2 feet of sea level rise by 2100. 

And the largest floods are expected to become more frequent. Today’s 100-year flood events, or those considered to have a 1% chance of happening in any given year, will happen about four to five times as often by the 2040s.

“So you start to see these widespread damages and consequences across the basin,” Mauger said.

One challenge of mitigating flooding effects is that there’s no one silver bullet, Mauger said. 

The watershed is impounded by five hydropower dams: two on the Baker River and three on the upper Skagit River. When flooding is projected, the Army Corps of Engineers operates Ross Dam and Upper Baker Dam for flood control.

Without the dams, the November 2021 floodwaters could’ve been 8 feet higher, the Skagit Valley Herald reported at the time. That’s because much of the rain fell upstream of the dams. But dams aren’t the panacea, Mauger said. 

For the top 10 largest Skagit floods (excluding December 2025), nearly half of the total flow has originated from areas unaffected by the dams in the watershed. 

And the current system — roughly 50 miles of levees in the Skagit — begin to overtop in some places at the 25-year event. 

The report didn’t specifically look at solutions, but in the future could be used to examine potential management options. Using the model, officials could see the implications of using certain modifications upstream (such as levees) for downstream communities, and where things like setting back dikes and levees and giving the river room to breathe could help. 

“We need to start having those conversations about how to increase resilience,” Spore said, “and hope that this tool can bring the community together to have those constructive discussions about shared risk and how we can work together to reduce future harms to the Skagit community and ecosystems.”