AK CASC scientists link the effects of snowpack changes on salmon in Alaska Park Science article

snow-capped mountains above a lake

AK CASC scientists Jeremy Littell and Stephanie McAfee are authors on a recent publication titled, “So Goes the Snow: Alaska Snowpack Changes and Impacts on Pacific Salmon in a Warming Climate,” in conjunction with the National Park Service.

As climate change alters conditions across Alaska, impacts will be varied in different parts of the state. For snow, though there is an overall trend towards shorter snow seasons and more rainfall-dominated watersheds in the long term, the coming decades will likely bring a range of changes across Alaska.

salmon in shallow water
Snow melt helps maintain cool temperatures and consistent stream flow for salmon. NPS Photo.

The paper considers changes in snow season length and snowpack— the snow that accumulates on the ground, persists through winter, and melts the following spring. These impacts vary across the state, with major decreases in snowpack expected in the coastal climate of Southeast Alaska, and modest increases in high elevation and latitude areas by the mid-21st century. This is because in locations that already remain near freezing in the winter, a small rise in temperature will prompt the transition from reliably snow-dominated winters to winters with a mix of rain and snow, and at lower elevations, from mixed rain and snow to rain-dominated winters. In colder locales the same increases in temperature will still be below freezing and thus not impact snow accumulation as immediately.

Snow is tied to the health and future of Alaska’s ecosystems and species. The future of Southwest Alaska’s abundant wild salmon runs, for example, will likely be impacted by the climatic changes expected for the region. Southwest Alaska provides a unique chance to study the relationships between climate, snowpack, and ecosystem function because of its geographic position at ecological transitions. 

Historically, most watersheds in Southwest Alaska have been snow-dominated. However, by the mid-21st century, the majority of watersheds in the region are projected to enter transitional climates, with low elevation watersheds becoming increasingly rain-influenced systems. By the 2050s, the snow season for much of the region is projected to decrease by one to five months and parts of the region may have no months with persistent snow cover.

For salmon, shifts in snowpack and snow season as well as glacial retreat could alter the health and productivity of the population. Declining snowpack alters the temperature, streamflow volume, water availability, and seasonal timing of runoff. These factors influence salmon spawning, migration, and survival patterns. For instance, in watersheds entering transitional or rain-dominant hydrologic regimes an increase in streamflow during winter months when salmon eggs are present in the gravel could increase the possibility of scouring and egg mortality during storms. 

As resource managers work to manage and protect salmon populations, considering these added stressors will aid in finding solutions that protect the ecological, subsistence, economic and cultural systems that depend on salmon in Alaska.