Some of the forecasted climate change impacts to the Pacific Northwest include:
- Increased winter precipitation and decreased summer precipitation
- Increased summer air temperature by 2080’s of 2.81 °C to 6.31 °C (5 to 11 °F)
- Increased winter air temperature by 2080’s of 2.44 to 4.28 °C (4 to 8 °F)
- Increased August stream temperature by 2080’s of up to 6 °C (11 °F)
- Reduced snowpack and earlier snow melt
- Changes in timing and magnitude of flow (earlier snowmelt peak, greater peak flood events, longer baseflow periods)
- Increased sediment transport rates of 200-400%
- Increased incidence and probability of forest fires
Habitat degradation is considered the leading cause for the decline of salmonid populations in the Nooksack watershed. High temperatures and low habitat diversity are the most significant factors limiting SF Nooksack early chinook in the lower SFNR, followed by high fine sediment load, lack of key habitats, low flows, and human disturbance (WRIA 1 SRB 2005). Some of the major impacts include:
- Low proportion and frequency of pool habitat.
- Reduction in availability of complex edge and floodplain habitats.
- Lack of instream wood and other forms of cover.
- Frequent high water temperatures that exceed optimal ranges or reach lethal limits.
- High proportion of fine sediment in spawning substrates.
- Decreased summer flows and higher peak flows.
- Degraded water quality (i.e. dissolved oxygen, pH, turbidity, nutrients).
Salmonids are particularly vulnerable to climate change because of their ectothermic (cold-blooded) physiologies and anadromous (living in both freshwater and marine water) life histories that require migration through linear stream networks that are easily fragmented (Isaak et al. 2010). Climate change impacts on temperature, flow and sediment regimes could profoundly affect physiology, behavior, and growth of individuals; phenology, growth, dynamics and distribution of populations; structure of communities, and; functioning of whole ecosystems (multiple authors, cited in Rieman and Isaak 2010), with increasing complexity and thus difficulty predicting impact at higher levels (Rieman and Isaak 2010). Climate change impacts to salmonids as a result of increased temperature can cause lowered dissolved oxygen, changes in growth of juveniles, changes in timing of emergence and migration, creation of thermal barriers to migration, disturbance to community structure, and increased occurrence of pathogens (i.e. Columnaris) or filamentous algae. The impacts of climate change due to changes in timing and magnitude of discharge may result in reduced habitat availability, reduced access to floodplain or side-channel habitats, or changes in timing or length of life history stages. Projected increased sediment with climate change may result in reduced egg-fry survival, changes in feeding behavior, biophysical injuries, or avoidance of habitats completely.
It is important to consider the pace of climate change and the ability of salmonids to adapt to that change. Salmonids do have the capacity to rapidly colonize new habitats, so to the extent that climate change will affect the distribution and availability of critical habitats, salmonids may be able to exploit what emerges, assuming such habitat is suitable and accessible (multiple authors cited in Rieman and Isaak 2010). Salmonids may also adapt over time through natural selection—evidence indicates evolution can occur within 10 to 20 generations (40-80 years; multiple authors, cited in Rieman and Isaak 2010) – although there is uncertainty about climate change outpacing evolution rates. Climate change impacts will affect every life stage of Chinook salmon, increasing the difficulty of adaptation.
Grah and Beaulieu (2013) discuss the implications of climate change and fish survival to members of the Nooksack Indian Tribe. Such climate changes will further adversely impact the Nooksack River in regard to available water, altered hydrographs and sediment dynamics, as well as suitable fish habitat and fish survival. As such, there is a real need to more accurately evaluate the hydrology, water temperature and sediment dynamics of the upper Nooksack River basin under today’s conditions and more importantly in the future under various accepted climate change scenarios. Thus, establishing an adequate baseline of conditions today is fundamental to detecting change in conditions in the future with continued and projected climate change.
Grah, Oliver, and Jezra Beaulieu. “The effect of climate change on glacier ablation and baseflow support in the Nooksack River basin and implications on Pacific salmonid species protection and recovery.” Climate Change and Indigenous Peoples in the United States. Springer, Cham, 2013. 149-162.