PRESSURE: Warming Temperatures Are Altering Salmon Streams
Climate change is threatening the clean, cold, and plentiful water in rivers that salmon need to survive. The average annual air temperature across Washington increased by 1.77 degrees Fahrenheit between 1960 and 2020,9 a trend that is projected to continue but at an even faster rate as heat-trapping atmospheric carbon dioxide levels continue to climb.
Glaciers, which provide cold water to streams in the Pacific Northwest, are vanishing. In addition, mountain snowpacks are becoming smaller over time as average temperatures increase and freezing elevations rise. The amount of water in streams in the summer, when young salmon are at a critical life stage, has become lower in most streams,10 and for longer periods of time. Scientists estimate that the amount of water that was released from melted snow declined 21 percent in the western United States from 1955 to 2016.11 Compounding the low-flow problem, water is being removed from rivers to irrigate farmland and accommodate an increasing human population.
As summer low flows decline and the air warms, water temperatures in rivers increase. Water temperatures greater than 64 degrees Fahrenheit stress salmon, and temperatures above 70 degrees Fahrenheit can be lethal.12 Without actions to reduce water temperatures, there will be fewer salmon and fewer rivers where they can survive.
The changing climate also is bringing rain instead of snow to some areas. With more rain, winter stream flow will increase by 25-34 percent by the 2080s, increasing the likelihood of severe flooding in the winter.13 Severe flooding becomes catastrophic when floodplains, which are natural storage areas for flood water, are developed for commercial and residential use.
As peak flows change in volume and season, the life cycles of salmon are being disrupted. More intense floods can destroy redds (salmon nests), reduce habitat complexity, and flush young salmon out of their calm-water habitat, reducing their chance for survival. While some juveniles may survive this premature transition from freshwater to saltwater, many won’t be large enough to catch prey or avoid being eaten.14
The amount of snow in the mountains is decreasing. Scientists project that the average spring snowpack in Washington will decline by 56-70 percent by the 2080s.13
Some Washington streams are getting hotter, stressing salmon. Scientists estimate that by the 2080s, an additional 1,016 Puget Sound river miles will exceed 64 degrees Fahrenheit for the entire month of August.12
As temperatures warm, the point that rain turns to snow moves higher up the mountain, decreasing the snowpack. Salmon count on plentiful snowpack to melt and deliver cool, clean water in the summer and during droughts. Less snowpack means less water. Less water means warmer water. Both threaten salmon and salmon recovery.14
PRESSURE: Climate Change in the Ocean
Human activities have resulted in record-breaking levels of carbon dioxide in the atmosphere and in the oceans.15 Excess carbon dioxide is absorbed by the ocean, forming carbonic acid, which increased the average ocean acidity level by 30 percent since the Industrial Revolution.16
Increased acidity damages the phytoplankton, zooplankton, and crustaceans salmon eat. Excess carbon dioxide also can change the way salmon use their sense of smell to find food, avoid being eaten, and find their natal streams.17
The warmer climate also impacts ocean temperatures. The near-surface average water temperatures off Washington’s coast have been warming during the past 50 years.18 Warmer water has fewer nutrients and less oxygen than colder water and creates conditions less beneficial for salmon. For example, warmer water favors sub-tropical zooplankton, which are poor food for juvenile salmon and the fish they eat, making survival less likely.
Salmon have demonstrated during the past 10,000 years that they can adapt to a changing environment. However, climate change is speeding up these environmental changes, and when combined with fewer natural buffers, degraded habitats, and their lost genetic diversity, salmon struggle to adapt quickly enough, threatening their continued existence.
There has been a 16 percent decline in rain-falling-as-snow since 1949. Across Washington, freezing levels have risen nearly 900 feet.
PRIORITIES AND PROGRESS
The climate crisis requires immediate action to reduce pollutants that are accelerating climate change and build climate resiliency for people and salmon. In 2021, Governor Jay Inslee signed the Climate Commitment Act into law, committing to reduce Washington’s greenhouse gas emissions by 95 percent by 2050.19
In addition, several grant programs are focusing on mitigating the increasing toll of climate change on watersheds. Salmon Recovery Funding Board grant applications require recipients to address climate resiliency and the innovative Floodplains by Design grant program supports floodplain reconnection and streambank protections, which can reduce the impacts of climate change. Without actions to reduce water temperatures, there will be fewer salmon and fewer rivers where they can survive.
Climate change is speeding up environmental changes and salmon are struggling to adapt.
Banner photograph by Angela-Schwart, Unsplash
Ocean photograph by Alice Rubin, Recreation and Conservation Office