Climate change is ramping up flood risk in the Pacific Northwest: Study

A powerful future earthquake, coupled with climate-driven surges in sea levels, could significantly increase flood risks in the Pacific Northwest, a new study has found.

These conditions could impact thousands of residents and their properties in Northern California, Oregon and Washington State, according to the study, published on Monday in the Proceedings of the National Academy of Sciences.

A major earthquake could ultimately cause coastal regions to sink up to 6.5 feet, expanding the federal-designated coastal floodplain by 35 to 116 square miles, the study authors determined.

They defined the coastal floodplain as the area that exhibits a 1-in-100 chance of flooding each year.

"Long-term effects could render many coastal communities uninhabitable," lead author Tina Dura, an assistant professor of geosciences at Virginia Tech, said in a statement.

Dura and her colleagues created tens of thousands of models to assess the amount of land sinkage that could occur after the next big Cascadia earthquake. They then used geospatial analysis to quantify earthquake-fueled expansion of the floodplain at 24 adjacent communities and estuaries.

Since earthquake timing remains uncertain, the team modeled the effects of such an event happening both now and in 2100, when climate-driven sea-level rise would exacerbate the impacts of any land sinkage.

If a major earthquake occurred now, the scientists determined that an additional 14,350 residents, 22,500 structures and 777 miles of roadway would fall within the post-event floodplain zone — more than doubling flood exposure.

Potential flooding would affect five airports; 18 "critical" care, rescue and education facilities; eight wastewater treatment plants, one electricity substation; and 57 possible contamination sources, such as animal feeding operations, gas stations and solid waste sites. 

"Today, and more so in 2100 as background sea levels rise, the immediate effect of earthquake-driven subsidence will be a delay in response and recovery from the earthquake due to compromised assets," Dura said.

While now the floodplain would expand at most from 35 to 116 square miles, by 2100, that zone could grow to up to 143 square miles, according to the study. At that point, a major earthquake could more than triple the flood risk for residents, structures and roads, the authors noted.

The region would also experience significant economic loss, as an increased inundation of tidal waters would render soil unsuitable for cattle grazing and farming, the researchers explained.

Other possible impacts include the erosion of natural systems and beaches, which act as storm surges and help dissipate waves during weather events.

"The impacts to land use could significantly increase the timeline to recovery,” Dura said.

She warned that ecosystem losses might not be recoverable, while movement away from the coast might be impeded by both existing human development and land features.

“The loss of intertidal wetlands directly impacts ecosystem services such as water filtration, habitat for fisheries and shorebirds, and carbon storage capacity,” Dura added.

Although the future flood status of the Pacific Northwest could be dire, it is far from unique around the world, according to the authors. They cited similar such zones off the coasts of Alaska, Russia, Japan, Indonesia, New Zealand and South America — emphasizing the global relevance of the research. 

Going forward, the scientists therefore expressed hope that these findings could help inform hazard assessments and mitigation strategies for communities worldwide. 

"Preparing for these compound hazards can minimize long-term damage, ensure resilient communities, and protect critical coastal ecosystems from permanent degradation," they concluded.