February 16, 2023

A new report recently released by the Washington Department of Fish and Wildlife calls for new strategies and policy tools to address consequences of increasing human demand for water and the effects of climate change on Washington’s rivers, streams and salmon.The paper articulates the need to better predict future shifts in precipitation and the effect on streamflow, understand how groundwater and surface-water interact, and estimate how climate change and other stressors will affect salmon survival and water availability for people across the state.In Washington, 14 steelhead and salmon species are listed as at-risk of extinction under the Endangered Species Act. The ongoing impacts of climate change and increasing human population pressures will challenge the ability of streams to continue supporting native fish and wildlife, including listed salmonids.Climate change is projected to result in widespread increases in winter streamflow, declines in summer streamflow, and increasing stream temperatures that will degrade habitat for many native aquatic species, especially cold water-adapted fish like salmon. Additionally, continued human population pressures will increase land-use change and habitat loss with unintended negative consequences for fish and wildlife.“We know that fish are dependent on specific streamflows over the course of the year,” said Tim Quinn, WDFW Habitat Program chief scientist. “Changes in streamflow associated with climate change and increasing human water needs will challenge salmon recovery efforts in Washington. This report also shows us that climate change and its impacts on streamflow is not just a future concern, but rather a current and ongoing issue — and one that we will need to address if we want to recover salmon.”Climate projections, says the report, indicate that many fish and wildlife populations will be negatively affected by increasing winter flooding, decreasing summer streamflow, and increasing stream temperatures. Human population pressures will increase land-use change and habitat loss with unintended negative consequences for fish and wildlife. These environmental changes may exceed the capacity for some species to adapt, especially fish species with the longest freshwater residence times that are most susceptible to changes in water quantity and quality (e.g., spring Chinook salmon, summer steelhead, coho salmon). Other expected outcomes are:— Pre-spawning mortality will increase in summer- and fall-spawning salmon due to warmer water and lower low flows. Projected stream temperatures will stress adult salmon. Declining summer streamflow will decrease the quantity and quality of juvenile rearing habitat, and in some cases delay and in others accelerate downstream smolt migration, creating mismatches in timing of adequate food and/or the absence of predators.— Fewer fish will survive beyond the fry stage due to increased winter flooding. Early life history stages of salmon may experience higher mortality as a result of higher flows that scour eggs and reduce the availability of slow-water habitat for rearing juvenile fish. Scour events will also increase sediment loads that can reduce primary productivity (photosynthesis) and, thus, the production of food for juvenile salmon.— Riparian habitat, stream shading, bank stability, and organic inputs will likely be negatively impacted by increased wildfire frequency and intensity. Over time, riparian vegetation is more likely to resemble adjacent upland vegetation, reducing its ability to provide riparian functions and increasing its susceptibility to wildfire. This may be especially significant in arid and semi-arid basins. Specific impacts of increased wildfires on riparian areas are complex, depending on local conditions and historic management, but these changes may have profound effects on riparian habitat availability and function. While riparian habitat makes up only a small proportion of the landscape, approximately 85% of wildlife species in Washington use or are associated with streams and rivers, with approximately 170 species requiring riparian habitat for some portion of their lives.Key information needs include:— Better estimate how aquatic plants and animals will shift in time and space. Distributions of native fish species are expected to shift northward (higher latitudes) and into higher elevations as stream temperatures rise. The rate at which different species or life stages can move is largely unknown. At the same time, invasive species will become more abundant and in many cases be better adapted to the new hydrogeological conditions. Major knowledge gaps include how inter-species interactions will change due to changes in distribution and how life-stage transitions (e.g., egg incubation timing, spawning initiation) will be affected bychanges to thermal and hydrological cues. This work is essential to the management of risk on species persistence.— Better estimate how climate change and other stressors will affect salmon survival. Life cycle modeling should be used to assess multiple stressors at each life stage of the life cycle and to estimate how cumulative effects at each life stage may affect population viability. Information on climate change impacts to species is most useful when it can be linked to growth and mortality at each stage of the species’ life history. Species currently believed to be at greatest risk should be given priority.The report includes two case studies – the Snoqualmie and Walla Walla watersheds.Climate change, says the report, is predicted to have the following significant impacts on the Walla Walla River:— Summer low flows will continue to decline due to declines in groundwater levels and changes in land cover. Land cover changes have had a substantial impact on low flows already. Shallow groundwater levels have already declined from historical levels and are projected to continue declining, with approximately 50% less water from historical levels by 2040. Although some snow does accumulate in winter, it is not enough to dramatically influence low flows. It is also already an arid watershed, so evaporation is not likely to change substantially in the future.— Stream temperature will likely increase across much of the basin. Upstream reaches have less water, which warms more readily than water in lower reaches. While water is more plentiful in lower reaches, it is exposed to higher air temperatures.— Wildfires are projected to increase substantially. Based on comparisons with similar locations, the likely effects on water quality and quantity will be an increase in flow during spring, increased water temperature, and increased sediment load.–Demand for water from large agricultural users is likely to continue increasing, which will decrease summer low flows and further increase water temperatures.Predictions of biological impacts for summer steelhead, spring Chinook, and bull trout in the Walla Walla watershed are:— Higher water temperatures in summer will likely increase adult mortality for all three species, especially for spring Chinook that reside in the river during summer for extended periods.— Juvenile mortality will likely increase due to reduced habitat area that increases competition among rearing juveniles, increases susceptibility to predators, and increases water temperatures in low-flow habitat areas.— Egg-fry mortality could be significantly increased in all three species due to increases in the frequency of winter high flow events large enough to mobilize streambed gravel and scour salmon redds.— Direct mortality of fish and other biota could increase due to increased severity of high flows.The report calls for coordinated water conservation planning among local, state, federal, and other partners to establish a science-policy forum to address instream water issues, prioritize regional knowledge gaps, and identify key areas for water resource protection and restoration. It also proposes advances in monitoring and adaptive management to better understand and maximize the benefits of restoration projects and other tools designed to enhance flows.

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An aerial view of a body of water.