HELENA, Mont. — In the shadow of hills and rock walls, the north entrance road at Yellowstone National Park normally traces the river, ferrying visitors from the outside world to a very different one teeming with wildlife and otherworldly geothermal features.
But large chunks of pavement are now gone on this crucial tourist corridor, washed away in a vicious June storm that swelled the Gardner River and sent mud and rocks racing down hillsides. Some road stretches were obliterated or left with half a lane — if that — with jagged edges that made it seem as if the river had taken big bites of asphalt.
In its 150th year, Yellowstone, the country’s oldest national park, finds itself at an existential crossroads in an age of climate change. It will rebuild after the flood damage, which has forced the two northern entrances to close for months. But the question is how, especially given the likelihood that flash floods, drought, wildfires and heat will dramatically change how the park can operate.
“We have a good sense of what’s coming down the line for us,” said Betsy Buffington, the Northern Rockies regional vice president for the National Parks Conservation Association. “What does rebuilding mean in this broader context?”
In the days after the storm, Yellowstone’s superintendent, Cam Sholly, suggested that old disaster measuring sticks have become outdated as climate change took hold. He described the recent storm as a “thousand-year event, whatever that means these days.”
“They seem to be happening more and more frequently,” he added.
The largest looming factor is a rapidly changing climate, which experts say contributed to the record flooding. An atmospheric river plus warm temperatures resulted in the equivalent of four to nine inches of rain in combined precipitation and snowmelt, according to NASA. The Yellowstone River just north of the park crested at 13.88 feet, smashing the previous record of 11.5 feet set in 1918.
If, as Mr. Sholly suggests, “thousand-year events” will happen far more often, National Park Service officials have to think seriously about whether it makes sense to rebuild roads and buildings in the same locations where they washed out. In some places, he said, parts of road slid 80 feet into the river.
With more rain-on-snow events, more flooding is expected. “A lot of the roads are historic stagecoach roads,” said Cathy Whitlock, a paleo-climatologist at Montana State University in Bozeman and an author of a climate change study of the park. “The park needs to be thinking about extreme events, the kind we haven’t seen before, and fortifying its buildings, roads and infrastructure.”
National parks across the country are confronting similar challenges. They are particularly vulnerable because many are at higher elevations, where the thinner atmosphere leads to warmer temperatures and where vanishing snow results in more ground absorption of heat, according to a 2018 study.
For now, Yellowstone officials are working to make sure that visitors can have some semblance of a vacation the rest of the summer. The southern portion of the park has reopened and the northern portion was scheduled to open on Saturday in time for the holiday weekend, though visitors will not be able to access it from the north.
The Federal Highway Administration has announced $60 million in quick-release funding to allow temporary fixes in the park, but the long-term rebuilding costs will soar far higher. The Associated Press recently estimated that the price tag could top $1 billion, though the National Park Service has not yet calculated a ballpark. “I am not going to give a high-level figure at this point,” Mr. Sholly said in an interview. “It’s going to be expensive.”
There have been no decisions on where to route the new road between Gardiner, a gateway community at the north entrance, and park headquarters at Mammoth. Mr. Sholly said rebuilding the same river route might be untenable because climate change made another catastrophic flood more likely.
He said the sections of washed-out road are “probably less than two miles, but they are in the worst areas for that to happen.” Aerial footage shows that in some places, floodwaters took out the entire roadway and reclaimed the river channel.
“I would rather see that river corridor restored,” he said.
The park’s northeast entrance also remains closed after parts of the main route there crumbled in the storm, cutting off the nearby tourist towns of Silver Gate and Cooke City.
Neither entrance is expected to reopen until the fall.
The problem this time was an inundation of water, but the opposite concern also has scientists worried. The snow line is creeping higher in the region, and the desiccated grasses, brush and tree limbs have become ready fuel for large wildfires.
Last year, wildfire fuels were so dry that the park suspended its policy of allowing natural fires to burn. The park has been thinning fuels through mechanical means around hotels, stores and other buildings to provide a defensive space should wildfires break out.
“We have seen fires burning where we haven’t seen them before,” Mr. Sholly said. “Last year, we had some of the warmest water temperatures and lowest water levels that we have seen in our rivers and streams.”
The park region, which has warmed 2.3 degrees Fahrenheit between 1950 and 2018, is probably as warm as or warmer than it has been in 20,000 years, according to paleo-climate records cited in Ms. Whitlock’s study. The dominant snow area level in 1950 was about 7,000 feet and by 2100 could be 9,500 feet, according to projections.
By 2060 to 2080, the park is projected to be 5 to 6 degrees Fahrenheit warmer than temperatures just before and after 2000, Ms. Whitlock’s study shows. Without mitigation, the temperature could rise a whopping 10 degrees by the end of the century.
Hotter and drier temperatures could also alter the park’s famous geothermal features, providing them with less water. A recent study found that during a megadrought in the 13th century, the Old Faithful geyser stopped erupting for decades. Geothermal features depend on a balance of water and heat.
Researchers are studying wildlife migration corridors outside the park to make sure that Yellowstone’s famous assortment of species, from grizzly bears to antelope, have ways to exit the park as it gets hotter. “If we want to protect the iconic wildlife of Yellowstone, we need to protect areas that wildlife need to migrate, move and maintain genetic diversity,” said Ms. Buffington, the conservation association vice president.
Cultural properties are also at risk. So far, it appears that the only park building to be damaged was a 1930s backcountry ranger cabin that washed away, Mr. Sholly said. An inventory of archaeological sites is underway to see if they sustained damage in the torrential rain.
As park officials rebuild, they will consider all of the potential impacts of climate change.
“What are the things we may not have thought of 10 or 20 or 30 years ago but will be thinking about 10, 20 or 30 years from now?” Mr. Sholly said.