A new flood-risk assessment for the Skagit River watershed projects that a flood considered a once-in-100-years event today could occur about four to five times as often by the 2040s as the climate warms. Led by the Swinomish Indian Tribal Community with partners including the University of Washington Climate Impacts Group, the project produced maps showing the expected depth and duration of river and coastal flooding in specific locations. The maps cover projections for the 2040s and 2080s and identify potential hazards for people, vehicles, homes and businesses, as well as places where dikes could fail. The work aims to give residents and local officials more detailed information for emergency planning and development decisions. The federal flood maps for Skagit County have not been updated since 1985, and some local officials have relied on paper maps, according to the project team. The model was nearly complete when a December flood led to evacuation orders for about 75,000 Skagit Valley residents. Project staff shared flood-model animations with county emergency managers during the response. “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,” said Heather Spore, environmental policy manager for the Swinomish Indian Tribal Community. The updated maps show that flood impacts vary across the valley. Hamilton is vulnerable across a range of flood scenarios, while some parts of Sedro-Woolley are projected to remain dry and could offer refuge. The information could also help residents identify unsafe roads and plan alternate evacuation routes. The assessment is not a regulatory tool, and jurisdictions are not required to use it. The maps and related materials are available at no cost through the project website. Climate change is expected to intensify flood risks through heavier storms, rising seas and a shift from snow to rain in the mountains that feed the watershed. The region’s peak snowpack has declined by about 25% since 1950, and projections indicate it could fall to less than half of historical levels by the 2080s. Models also project that the heaviest storms will become about 22% more intense on average by then, while Skagit, Padilla and Samish bays could see 1.5 to 2 feet of sea-level rise by 2100. Those changes add pressure to a watershed where more than half of Skagit County’s population of over 130,000 people is exposed to flooding. Floodwaters also threaten businesses and salmon habitat. Five hydropower dams operate in the watershed, and the Army Corps of Engineers manages Ross and Upper Baker dams for flood control when high water is expected. But dams cannot control water flowing from every part of the basin, said Guillaume Mauger, Washington’s state climatologist and a research scientist with the University of Washington Climate Impacts Group. Nearly half the flow in the 10 largest Skagit floods, excluding the December 2025 flood, came from areas not affected by the dams, according to the assessment. The valley also has about 50 miles of levees, some of which begin to overtop during a flood with a 1-in-25 chance of occurring in a given year. The assessment did not recommend specific fixes, but its modeling could help officials evaluate options such as setting back levees and dikes to give the river more room. “We need to start having those conversations about how to increase resilience,” Spore said, adding that the tool could help communities discuss shared risks and ways to reduce future harm to residents and ecosystems.