Record-early Alaska river breakups are part of a long-term warming trend

Breakup-related betting events on both the Tanana and Kuskokwim rivers just recorded their earliest dates ever.

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A 2008 photo shows the Nenana Ice Classic tripod on the Tanana River. (Frank Kovalchek / CC BY 2.0 via Wikimedia Commons)

When a wooden tripod dropped from the last bit of melting ice into the flowing water of Alaska’s Tanana River just after midnight on Sunday, it was more than the earliest recorded breakup of ice in the century-old Nenana Ice Classic betting pool.

That breakup and the record-early April 12 breakup of Kuskokwim River ice in the southwestern Alaska city of Bethel are part of a long-term trend toward less freeze and more open water in Alaska’s rivers.

Until Sunday, April 20 was the earliest recorded breakups for both the Tanana River at Nenana, a town about 55 miles southwest of Fairbanks, and the Kuskokwim River at Bethel.

The record-early breakups come at the end of a winter that was significantly warmer than normal throughout Alaska and adjacent parts of Canada.

They also followed Alaska’s warmest March on record, with temperatures soaring 15.9 degrees Fahrenheit above average, a February with record-high temperatures along western Alaska and a second consecutive winter with extremely low levels of ice in the Bering Sea.

While this year’s early spring is “extreme,” these conditions will become more common in the future, said John Walsh, chief scientist at the International Arctic Research Center at the University of Alaska Fairbanks.

“That’s a preview of what we might be seeing and of what we’re going to see in an average year 30 to 40 years from now,” he said.

Shorter ice seasons on the rivers have profound impacts for rural residents who depend on frozen rivers for travel.

“The rivers are our main transportation routes,” said Mark Leary, an official with one fo the local tribal governments. “If we’re not able to travel on the river, we’re all 100 percent dependent on air travel, which is hugely expensive.”

Unreliable ice is also dangerous, said Leary, who works with the volunteer Bethel Search and Rescue organization.

Last month, four people died when their vehicles dropped through slush or holes in the thin Kuskokwim ice. The deaths happened in separate incidents; two of the victims were driving snowmobiles and two were driving all-terrain vehicles.

In the latter case, which happened on the last day of March when river conditions were more similar to those seen in May, Leary and his colleagues tried to warn the travelers, who were in a group of five riding all-terrain vehicles.

“They actually drove by us, and we tried to stop them,” he said. The search-and-rescue group wound up saving the lives of three of the five travelers.

Climate scientists also have good reasons to pay attention to river breakup dates.

River ice reflects conditions over entire seasons and over broad geographic regions, said Brian Brettschneider, an Anchorage-based climatologist and researcher with the International Arctic Research Center.

“It’s a proxy for what the climate has been like for the last five months,” he said.

River breakup is a clearly defined end of winter, and — at least in Alaska — it is unaffected by factors like urban heat islands or industrial construction, he added. “In many respects, it’s the ultimate unpolluted, if you will, climate variable,” he said.

The Nenana Ice Classic in particular provides useful scientific information about the trend away from ice to free-flowing water.

The betting pool, started by Alaska railroad engineers in 1917, has become an iconic Alaska tradition. It is managed by the Nenana Chamber of Commerce and raises money for local nonprofits. It uses a system of wires to connect the tripod to a clock; when the tripod falls, the wires are tripped and the clock stops, determining that year’s official breakup time. The methodology has been constant year to year, a boon for scientists, including those from NASA.

“That’s a good 100-year record that, as far as well can tell, is a very consistent record,” Walsh said.

Typical breakup dates of the Tanana River, a tributary of the Yukon River, used to be after the first week of May, according to Nenana Ice Classic records. By 2015, breakup was usually occurring at the end of April.

The story is nearly the same at the Kuskokwim River  There is a similar but much-younger betting pool, the Kuskokwim Ice Classic, but the National Weather Service has records that predate the startup of that event.

In the past, breakup in Bethel typically occurred in mid-May, according to the 92 years of records kept by the National Weather Service. Since 1980, according to the records, breakup there has advanced by about a week —not counting this year’s record-smashing early melt.

The trend continues on the Yukon River in nearby Canada. Breakup of the river at Dawson was about five days earlier at the end of the 20th century than it was at the beginning of the century, according to research by the late Rick Janowicz, a long-serving hydrologist who worked for the Yukon Government.

Even more dramatic than the rivers’ early breakup is a shift in how late they freeze for the winter.

Accounts from the Klondike Gold Rush by journalist Tappan Adney and others describe ice forming in rivers in mid-September and rushed travel by steamship to reach the Bering Sea before freeze-up made the Yukon River impassable.

Even as recently as the early 2000s, the Kuskokwim and Yukon rivers were usually sufficiently frozen in November to allow safe vehicle travel, according to National Weather Service records.

But in the winter of 2018-19, there was so little river ice around Bethel on the river that the Kuskokwim 300, an important 300-mile sled-dog race held each January and used as a qualifier for the Iditarod Trail Sled Dog Race, has to be converted to a series of 75-mile laps to avoid large areas of open water. Prior to that race, a family of five traveling the river to watch New Year’s Eve fireworks in Bethel had to be rescued when their snowmobiles fell through the ice.

This winter, the Kuskokwim’s ice also came late and was unreliable. Ice remained thin and pocked with holes even in December, according to Bethel Search and Rescue. By February, the ice was no longer safe for travel, according to the group.

For the Kuskokwim, low river ice has a connection to low Bering Sea ice, Brettschneider said.

“There’s probably one degree of separation. The warm Bering Sea really contributed to warm temperatures in Alaska, and then it’s the warm temperatures that prevented the river ice from getting really thick,” he said.

That extra warmth from the open Bering Sea added to long-term warming, he said, leading to poor freeze and early thaw on the Kuskowkim River. “We had a bad situation that was made worse because of bad ice,” he said.

The trend toward later freeze-up is pronounced across the border in Canada, according to Janowicz’s research. At Whitehorse, freeze-up of the Yukon River was occurring a full month later at the end of the 20th century than it was at the beginning of the century, according to Janowicz’s research.

In recent winters, the river has failed to fully freeze at Dawson, forcing some alternatives for Yukoners who relied on ice bridges in the past.

Along the lower Kuskokwim River, the shortened ice season has forced some lifestyle changes, Leary said.

Among them are the food-gathering practices, he said. Spring waterfowl hunting — an activity that engages “every male over the age of 10” — was normally done by snowmobile, he said. “But that doesn’t look like it’ll be the case this year. So people will be doing it by boat,” he said.

To address future winter-travel problems, he said, Bethel Search and Rescue has started raising money to buy an airboat, a vehicle that will be able to travel in the full range of conditions expected on the river — ice, slush and open water.