Arctic Growing Seasons Are Getting Longer

From the National Park Service Arctic Inventory and Monitoring Network's Landscape Dynamics Monitoring Brief, 2021.

A photo from the remote camera at the Mt. Noak climate monitoring station, Cape Krusenstern National Monument, June 6, 2019. The many white spots are Dryas flowers. National Park Service.

The National Park Service's Arctic Inventory and Monitoring Network (ARCN) tracks the timing and length of the growing season and the snow season in the five national park units of northern Alaska. Ecologist Dave Swanson uses remote automated cameras and satellite images to follow these seasonal changes.

Key findings

• The start and end of both the continuous snow season and the green season vary by about a month from year to year, and ground cameras confirm the satellite results are realistic.
• Spring is arriving earlier. By 2020, snow across ARCN melted out about 8 days earlier on average, and spring green-up came about 11 days earlier, than in 2000.
• Fall is ending later. By 2020, the green season ended about 11 days later and the snow season began about 5 days later than in 2000, though fall dates are less certain because of clouds and the low autumn sun.
• Peak midsummer greenness differs greatly from place to place with vegetation density, but stays fairly steady from year to year in any one place.
• Across much of ARCN, vegetation has grown very gradually greener since 2000 as plants became taller or denser.

Top: average dates of the end of the continuous snow season and start of the green season. Bottom: average dates of the end of the green season and start of the continuous snow season. ARCN, 2000–2020. National Park Service.

Trends in the end of the continuous snow season, 2001–2020. Red, pink and yellow areas, covering most of ARCN, show a trend toward earlier snowmelt, highly significant in the red areas. The strongest changes were in Bering Land Bridge and Noatak National Preserves, and a large area north of the parks also trended earlier. National Park Service.

How the seasons are monitored

ARCN has five remote automated cameras, one in each park unit, each taking five photos a day year-round. They record snowmelt, the flowering and leaf-out of selected plants, fall leaf color and the return of winter snow. Their view is very local, but it provides an important check on the satellite record. Satellite images from MODIS, available daily since 2000, show the coming and going of snow cover, spring green-up, fall senescence and peak greenness, and their frequency lets scientists use every clear day.

Why it matters

Changes in the timing of the snow and green seasons are likely to affect the movements and survival of wildlife, especially migratory animals such as caribou and birds, and the length of the season when people can travel through the parks on snow. Over the long term, longer growing seasons will let trees and shrubs spread into new areas and grow taller and denser.

Sources

• National Park Service, Arctic Inventory and Monitoring Network, "The Arctic growing seasons are getting longer," Landscape Dynamics Monitoring Brief, 2021. https://www.nps.gov/articles/000/arctic-growing-season-2021.htm
• Full NPS Natural Resource Report: https://irma.nps.gov/DataStore/Reference/Profile/228675