Landslides, floods, smoke: Prepare for climate change effects in Denali National Park

Landslides triggered by permafrost thaw, floodwaters gushing from melting glaciers and smokier air from bigger and more frequent wildfires are among the problems that a warming climate is expected to create for people traveling in Denali National Park and Preserve, according to a new report.

A transportation plan for Denali, released Thursday by the National Park Service, identifies climate change as one of several challenges looming for transportation in the park, site of North America's tallest mountain and one of the top visitor destinations in Alaska.

The plan considers other factors as well, including the quality of wildlife viewing and other visitor experiences, visitor safety, protection of the park's quiet atmosphere and overall environment, and the status of access routes to the park entrance.

The plan is not a decision and does not make specific recommendations, but it outlines factors that should guide future management over the next 20 years, the National Park Service said.

"This is really a broad sweep saying we need to pay attention, and we need to pay more attention," said Molly McKinley, outdoor recreation planner at Denali.

The park is already known for its strict transportation rules. A single 92-mile road goes into its heart, and very few private vehicles are allowed past the first 15 miles. Most visitors use park shuttle buses for day sightseeing trips or to reach campgrounds and backcountry hiking destinations. The park is also an important destination for pilots flying small planes; ski-equipped aircraft ferry mountain climbers to remote glacial base camps and carry sightseers who want to view 20,310-foot Denali and other Alaska Range peaks from the air.

As is the case for the rest of the far North, Denali is expected to get warmer in coming decades. Average annual temperatures are expected to be 4.6 degrees higher by 2040 and 8.2 degrees warmer by 2080, with the biggest changes likely to come in winter, according to the state government's Alaska Region Climate Change Response Strategy, the plan notes.

"This increase in average temperatures is expected to have a major impact on transportation resources within the park," the plan says.

Denali is already showing effects of climate change, including accelerating glacial melt, expansion of woody plants to higher elevations and latitudes, and slumps in the landscape caused by permafrost thaw.

Those changes in the natural world can affect people traveling by foot, vehicle, boat or airplane, the transportation plan says. Floods from glacial melt could swamp road, trail or airstrip sections, for example, and increased wildfire smoke can create hazards for air travel.

The spread of bushes could also affect visitors' enjoyment, McKinley said.

"As the brush gets higher, the experience of driving along the park road is expected to change," she said. If brush gets in the way of people trying to view animals, park managers will have to decide what to do, she said.

Even the distribution of visitor crowds is potentially affected, the plan says. Milder spring and autumn weather is likely to increase what is now considered the offseason for the park, and thus increase demand for transportation and visitor services, the plan says.

The park road is particularly vulnerable to changing conditions, notably permafrost thaw, the plan says. Denali sits atop the boundary between continuous permafrost, in which is the area fully underlain by frozen soil, and discontinuous permafrost, which is the area where permanently frozen soil exists in patches.

"As temperatures rise, the boundary between continuous and discontinuous permafrost is expected to migrate north. This will expose the Park Road to an increasing change of subsidence-related damage," the plan says, resulting in more maintenance.

Of 141 sites along the road already analyzed, 24 percent are considered to be in poor condition, at risk for landslides or debris flow problems, rock falls, frost heaves or severe erosion, the plan says. Only 9 percent of sites are in good condition; the rest were classified as being in fair condition, the plan says.

Some climate-related problems along the park road have already emerged.

In October 2013, a 600-foot-long, 110-foot-wide mass of partially thawed permafrost chunks — at least one the size of a small cabin — slid onto the park road and blocked passage. Some smaller slides occurred in the summer of 2016; one temporarily closed the road at Mile 67 and stranded some visitors.

The 124-page Denali transportation document is part of a joint National Park Service-U.S. Department of Transportation initiative that aims to guide transportation management over the long term, McKinley said.

So far, Denali is the only Alaska national park with its own plan. The national program assessing parks' transportation needs is being crafted in accordance with federal transportation legislation signed by President Barack Obama in 2012. Only a few other parks around the nation have completed similar plans, McKinley said.

The plan can be updated in the future as more information becomes available, she said.

The National Park Service is accepting public comments on the plan until Oct. 2.