Powerful autumn storms have sent surges of seawater as far as 20 miles inland onto the tundra of southwestern Alaska, and such flooding is expected to become more frequent as the climate changes, according to a study published in the current issue of the journal Arctic.
The study, by scientists with the U.S. Geological Survey's Alaska Science Center and the University of Alaska Fairbanks, examined the past century's storms and the floods they created on southwestern Alaska's Yukon-Kuskokwim Delta. The scientists used historical records dating back to 1913 and satellite imagery from the last two decades to quantify storm-caused damages.
The biggest seawater surges, they found, were in 1974, 2005 and 2011, each from storms so intense they would be expected to occur only once every 50 years.
The 2011 Bering Sea superstorm -- nicknamed "blizzicane" and "burricane" for its combination of hurricane-force winds and blowing snow -- wreaked havoc all along Alaska's Bering Sea coast. It struck in early November, created widespread flood and wind damage and resulted in one death.
Over the past century, only the 1974 storm -- also a November event -- was more powerful, according to the study. Interviews with the region's elders indicated that a 1931 storm was of nearly the same intensity, the study said.
For the more recent storms, satellite imagery -- especially imagery collected by cloud-penetrating radar -- provides detailed information about the extent of storm-surge flooding, said Craig Ely, a USGS biologist and co-author of the study. But reconstructing storms that struck before the satellite era was not an easy task, Ely said.
Storm-driven seawater inundated areas where people do not live, so there are spotty historical records, he said. There is a dearth of tide data for southwestern Alaska, though Nome has useful records on tides and weather events, he said. To help piece together past storm history, he and his co-authors examined driftwood piles, estimating when they were moved up from the shoreline. "It's a little bit tricky," he said. "You can have floods that go over the top of old driftwood and don't float it up."
The scientists explored remnants of old settlements that had been abandoned after they were flooded in big storms. One example, Ely said, is the changing location for the Cup'ik village of Chevak. A site now known as Old Chevak served as a refuge for flooding victims in 1931, according to elders' accounts, and subsequent flooding caused people to abandon that site for what is today's Chevak, a village of nearly 1,000 people that is located on the Niglikfak River.
With fall sea-ice cover reduced and other interrelated changes in the region's climate, the storms and resulting surges are expected to become more frequent, according to the study.
"We know that summers are warmer and ice formation is occurring later," Ely said. Less ice means that storm waves can more easily reach land, he said. And the exposed, dark-surfaced seawater absorbs solar heat, so wider areas without ice result in more retention of energy in the seas that feeds storm systems, he said.
In addition to the heavy tolls taken on people in the region, the surges of salty seawater can be expected to have various ill environmental effects: harm to freshwater ponds and non-saline habitats, hastened permafrost thaw and damages to nesting birds' habitat. If storms are early enough, Ely said, the seawater surges can wipe out birds' nests, as happened to Emperor goose nests destroyed by a June 2012 storm. However, the major fall storms detailed in the study struck after birds migrated south, he said.
Not all of the storm surge effects are bad, Ely said. The water unleashed by storms can move fish between ponds, sometimes to their benefit, he said. And the surges bring lots of sediment from the sea to the flat landscape, he said. "If they don't get sediment deposition, they can't keep up with sea-level rise," he said.