More than a third of coastal Alaska structures may be at risk of flooding by 2100
In the fall of 2016, an unusually strong storm hit the coastal Native village of Kipnuk, Alaska, causing ocean water to flood into the community. The storm surge inundated the lowland area where Rayna Paul and her family lived. While they evacuated to the town's school on four-wheelers, a wave slammed into the boardwalks they were driving on, and Paul's nephew, then just 8 years old, started floating away. Paul grabbed him by his coat.
"The thought of losing my nephew was unimaginable," she said.
They made it to safety, but cleanup and repairs took months. Four-wheelers were found floating in a nearby lake, and anything that hadn't been secured before the flood was scattered around the town. "It was the worst experience," she said. "This is a harsh reality that tribes from our region face." Paul now works as the environmental director for Kipnuk, and her responsibilities include planning to protect the community from future floods.
As climate change continues to spur sea level rise and increase hurricane intensity, mapping possible future flooding is crucial. A new study, published in Scientific Reports, used community accounts of past floods to show how sea level rise is likely to make future floods worse. The work adds to scientists' understanding of how climate change could affect Alaska's coastal communities as part of a broader effort to improve flood modeling in the state.
The data in the new study are "really important context for flood planning," said Richard Buzard, a geologist at the U.S. Geological Survey (USGS) and lead author of the new research. Buzard completed the work as a doctoral student at the University of Alaska Fairbanks.
Old Observations, New Database
Models of future flooding are checked, or validated, with observations of past flood frequency and severity. Flood modelers can use the record high flood elevation in a community as a proxy for that information. But in rural, coastal Alaskan communities, much of this kind of historical data exists not in a central database but in the memories and records of community members.
Remote coastal communities in Alaska, where climate change is acutely felt and rapid changes are observed, are often forgotten or underappreciated.
"Remote coastal communities in Alaska, where climate change is acutely felt and rapid changes are observed, are often forgotten or underappreciated," said Nora Nieminski, a geologist with the Alaska Department of Natural Resources' Coastal Hazards Program who was not involved in the new study. Flooding can be especially devastating for these tiny communities, which may have limited resources to repair damage.
To obtain the historical data necessary to improve flood modeling, researchers gathered spoken or written accounts, photographs, and videos from residents going back to 1887. Some of the records were gathered in interviews between Buzard and community members knowledgeable about flood history.
The collection of records, called the Flood History Database, continues to be updated by scientists from the state of Alaska, USGS, NOAA, and the National Weather Service. The records present the "unique methods we need to use to fill in data gaps," Nieminski said.
In the new study, researchers used the historical accounts to estimate current and future flood exposure. They compared record flooding to topography and the locations of buildings in 46 communities under two scenarios: 0.5 meter (1.6 feet) and 1.0 meter (3.3 feet) of sea level rise by 2100. NOAA estimates that global sea level will rise between 0.3 meter (1 foot) and 2 meters (6.6 feet) by 2100.
The team found that currently, 22% of structures in coastal Alaskan communities are located within the record high floodplain, putting them at risk of flood damage. Under the 0.5-meter scenario, that number rose to 30%. But under the 1.0-meter scenario, the proportion of structures at risk grew to 37%.
In each scenario, more than half of the structures at risk from flooding were residential.
Paul said she's always concerned about flooding in Kipnuk and is starting to notice more frequent flood events each year.
The authors noted that flood risk is a function of geopolitical and colonial forces, too. According to a 2022 report from the U.S. Government Accountability Office, Indigenous communities are often located in coastal areas because that's where the federal government built schools that Indigenous children were mandated to attend. Decisions about where to build didn't necessarily consider flood hazards, Buzard said.
They could have a high proportion of exposure to flooding. But they might not be prioritized as highly.
Small, rural communities face systemic obstacles to obtaining federal assistance to address flood exposure due to population size thresholds, the authors write. "These are low-population communities, and that has been a disadvantage at times," Buzard said. "They could have a high proportion of exposure to flooding. But they might not be prioritized as highly." He hopes the research will help decisionmakers better understand the threats these communities face.
Future Flood Modeling
The new study is a "stepping stone" in a larger effort to better model how and where floods happen in coastal Alaska, Buzard said. The data will ultimately be used for community-specific assessments of flood-related hazards, such as erosion or property damage. Such assessments help communities like Kipnuk develop plans to mitigate flood hazards, Paul said. "They help us better prepare for natural disasters."
Buzard is part of a team working to adapt a widely used USGS flood model, the Coastal Storm Modeling System (CoSMoS), for use in Alaska. Arctic environments such as coastal Alaska require a different modeling approach than the original CoSMoS uses because sea level rise also interacts with factors such as sea ice, he said.
"All these pieces of information are really crucial to guide safer development and planning for each of these communities," Nieminski said.