The purpose of this appendix is to identify possible future climate change impacts in the Columbia River Basin, based on literature review and available climate change studies. Most predicted impacts are associated with projected increases in air and water temperatures and include increased stress on coldwater fisheries sensitive to a warming aquatic habitat, potentially improved habitat for invasive Dreissenid mussels having implications for maintenance of hydraulic structures, and increased risk of watershed vegetation disturbances due to increased fire potential. Drought and hot, dry weather have led to an increase in outbreaks of insects in the Columbia Basin, especially mountain pine beetle, and insect outbreaks are likely to become more common and widespread. Other warming-related impacts include pole-ward shifts in the geographic range of various species, impacts on the timing of arrival and departure of migratory species, amphibian population declines, and effects on pests and pathogens in ecosystems. Climate change can also trigger synergistic and cascading effects in ecosystems and exacerbate non-native and invasive species problems.
Changes in hydrologic flow regimes and warming stream and reservoir temperatures caused by a warming climate will pose significant threats to aquatic ecosystems and are expected to alter key habitat conditions for salmon and other cold water aquatic species such as trout. For example, bull trout require very cold headwater streams for spawning, and a warming climate may disproportionately affect this species. Salmonids and other cold water species currently living in conditions near the upper range of their thermal tolerance will be particularly vulnerable to increased mortality and susceptibility to disease from higher water temperatures.
Anticipated climate change effects in the Northwest include specific hydrologic changes such as increased frequency and severity of winter flooding in mixed rain-snow basins. Region-wide increases in winter flows and summer temperatures, combined with lower summer flows, will threaten many freshwater species, particularly salmon, steelhead, and trout. Higher winter water temperatures also could accelerate embryo development and cause premature emergence of fry in basin tributaries. Rising temperatures will also increase disease and mortality in several salmon species such as spring/summer Chinook and sockeye, especially in interior Columbia and Snake river basins. Some Northwest streams have already warmed, on average, over the past three decades, contributing to changes such as earlier Columbia River sockeye migration.
As species respond to climate changes in various ways, there is also a potential for ecological mismatches to occur, such as the timing of emergence of predators and their prey. For example, increases in stream temperature are expected to result in greater habitat overlap between juvenile Chinook salmon and predatory non-native species such as bass in the early summer, as well as greater abundance of bass and other warm water predator species.
Climate change could also have significant effects on mainstem Columbia and Snake river flows and habitat in terms of runoff timing, water quantity, and temperature, impacting salmon in various ways. It is believed that mainstem temperature increases would accelerate the rate of egg development of fall Chinook, which spawn in the mainstem of the Snake and Columbia rivers, leading to earlier emergence at a smaller size than historically. Smaller-sized fry are likely to have lower survival due to increased vulnerability to predators, and predation rates would also likely increase. Potential impacts of increased water temperatures on adult salmon migration in the mainstem include delays in dam passage, failure to enter (or exit) fish ladders, increased fallback, and loss of energy reserves due to increased metabolic demand. Increased adult salmon mortality may also be caused by fish pathogens and parasites, as these organisms often do not become injurious until the host becomes thermally stressed.
Changes in freshwater flow into the Columbia River estuary caused by climate change are expected to be less than those caused by the hydrosystem. However, some changes in estuary habitats may occur. For example, sea level rise, in conjunction with higher winter river flows, could cause the degradation of estuary habitats created by sediment deposition from increased wave damage during storms. Numerous warm-water adapted fish species, including several non-indigenous species, normally found in freshwater have been reported in the estuary and might expand their populations and range with warmer water and seasonal expansion of freshwater habitats. Climate change also may affect the trophic dynamics of the estuary due to upstream extension of the salt wedge in spring/early summer caused by reduced river flows. The upriver head of the salt wedge is characterized by a turbulent region known as the estuary turbidity maximum, an area with high concentrations of fish food organisms. Changes in the upstream extension of the salt wedge will influence the location of this zone, but it is difficult to forecast the effect this change will have on juvenile salmon.
Scientific evidence strongly suggests that global climate change is already altering marine ecosystems. Physical changes associated with warming include increases in ocean temperature, increased stratification of the water column, and changes in the intensity and timing of coastal upwelling, as well as increases in ocean acidification and hypoxia events. These changes will alter ocean productivity, the structure of marine communities, and, in turn, the growth, productivity, survival, and migration patterns of anadromous fish.
The possible changes in regional snowpack, river flows, temperatures, and reservoir elevations due to climate change could have a profound impact on the success of habitat restoration efforts under the program and the status of Columbia River Basin fish and wildlife populations. The Independent Scientific Advisory Board produced a report on potential climate change impacts in the Columbia River Basin. See ISAB Report 2007-2, Climate Change Impacts on Columbia River Basin Fish and Wildlife.