After an unusually cold spring, forecasters are cautioning that this year’s breakup of Alaska’s major rivers pose a heightened risk of flooding for dozens of communities along the riverbanks.
While in places like Anchorage, spring breakup means the end of winter — muddy roads, Xtratufs and tire changeovers — in more rural communities that rely on rivers as a source of transportation, breakup season can be a time of anxious waiting. The ice is too thin for walking or snowmachining, and the water is too full of ice and debris to safely boat along. And there’s the looming possibility of ice jams, which can cause water to swell over riverbanks, flooding communities and homes.
This year, for nearly all of Alaska’s largest rivers — including the Yukon, Tanana, Kuskokwim and Koyukuk rivers — there is an above-average potential for spring flooding, according to Celine Van Breukelen, a hydrologist with the Alaska-Pacific River Forecast Center, which closely tracks breakup each year.
The increased flood risk is due to two major factors: above-average snowpack and below-average temperatures in April throughout most of the state, which together have delayed melting and increased the risk of a more dynamic breakup, Van Breukelen explained.
So far, breakup is one to two weeks behind schedule, according to the National Weather Service. The Tanana River from Salcha up to Tanacross has broken up, according to a breakup report updated Tuesday. But most of the major rivers are still coated with ice.
“Not much has happened yet,” Van Breukelen said.
Flooding is likely — but exactly where is hard to predict
Spring air temperatures are the biggest factor for when and how the rivers will break, followed by snowpack depth and river ice thickness. Higher temperatures through April often lead to what scientists call a thermal breakup, which causes more gradual melting events and little flooding.
Dynamic breakups — which are what scientists predict will happen this year — occur when temperatures stay lower for longer and then rise substantially late in the season, causing snow and river ice to melt all at once. Ice jams occur when less-intact ice moves downriver and comes into contact with unmoving ice, forcing water over riverbanks and into villages and homes.
In late May 2013, one of the worst dynamic flooding years in recent history, an ice jam at Bishop Rock blocked up the Yukon River, flooding every building in Galena. Van Breukelen said April temperatures this year have been similar to what they were in 2013.
Because of the vastness of the state’s river system, exactly where flooding might occur isn’t always easy to predict with any precision, said Jeremy Zidek, a spokesman with the Alaska Division of Homeland Security and Emergency Management.
“In these above-average flood potential years, we typically do see some type of flooding somewhere, but the severity and the location is not possible to determine,” Zidek said.
Last year, Manley Hot Springs flooded during spring breakup due to an ice jam on the Tanana River, forcing dozens of people to evacuate — an event that no one had predicted, he said.
One way that Alaskans can help improve breakup forecasts is by submitting river condition observations to Fresh Eyes on Ice, a citizen science project out of the University of Alaska Fairbanks.
The photos — which can be submitted through the university’s webpage, via a smartphone app developed by NASA or on social media — are sent to the National Weather Service, which is used to help validate satellite imagery. The university is making a push for more observations this year given the increased flood risk.
Because it can be hard to know where flooding might occur, Zidek encouraged Alaskans in communities near major rivers to take precautions now in case of disaster. Those recommendations include:
• Talk about flood risk with friends and family members, making sure they know that it might become necessary to move to higher ground. Have a plan.
• Move boats, vehicles and heavy equipment away from the river, and make sure boats are accessible in case they’re needed during a flood.
• In case you need to evacuate, have a “go” bag ready that includes identification and other important documents, a change of clothes, medication and personal hygiene items.
• Store important documents and valuables in plastic bags and in high places, like the tops of dressers.
• Gather pet food and supplies as well, and know where pets can be relocated or sheltered during a flood.
Ice jam or ice dam flooding is often a very sudden event, which is why advance planning is so important, he added.
“The ice dams are going to occur where they occur,” he said. “And when that happens, the water levels rise very quickly.”
Correction: This story has been updated to reflect that the 2022 spring flooding in Manley Hot Springs was caused by an ice jam on the Tanana River, not the Nenana River.