The Future of Instream Water in Washington State: A Brief for Policy Makers

Maintaining instream water for fish, wildlife, and people is a 21st century challenge. Losses of instream water have been largely due to increasing human demands for out-of-stream uses, and climate warming due to global anthropogenic greenhouse gas emissions. For many areas of the state, climate models project further increases in winter streamflow, consequent declines in summer streamflow, and increasing stream temperatures. These impacts will, in places, be made worse by changes in land cover, and by new demands for water. The warming climate will cause changes in seasonal irrigation demands that are likely to further reduce summer low flows, and increase summer stream temperatures. Some new municipal water demands will be met from deep groundwater sources, but others will tap shallow groundwater or surface water, increasing evaporation losses. Instream water reductions will be greatest where both urban and rural losses accrue, especially during summer. These pressures will further degrade habitat quantity and quality for many native aquatic species, and particularly cold water-adapted fish like salmon¹. Water conservation and storage measures may relieve some increases in demand, but the manifold environmental impacts associated with climate change are likely to exceed the capacity of native fish and wildlife to adapt, and will not be easily mitigated.

This brief does not specify solutions, but it is worth emphasizing that the current framework for managing water availability (both regulatory and non-regulatory) does not always meet existing fish and wildlife needs or proactively address future challenges. We need a holistic approach deploying a suite of existing and potentially new tools to ensure adequate water for fish and wildlife given the challenges of climate change that we have outlined here.

Here we characterize the principal bio-physical challenges, intending that shared understanding of these challenges will contribute to effective and enduring solutions. These will require coordinated planning among local, state, federal, and other partners, creation of a science-policy forum to guide the process, identification of regional knowledge gaps, crafting of effective measures, and prioritization of areas for protection and restoration of streamflows.

Throughout this brief, the needs of native salmonids are highlighted for the same reasons that justify growing investment in their recovery: their needs are shared by many other species, they are widely distributed, and our wellbeing would be greatly diminished without them.

The brief lists proactive actions intended to reduce uncertainty, in support of informed and deliberate choices about our future. One includes the creation of a science-policy planning framework that addresses land-use and water management on a regional scale. The state recently passed legislation to “include climate resiliency” into Growth Management Planning. This should be expanded to other forms of land-use planning. Further important actions include:

• Better predict future shifts in precipitation and their effects on streamflow.
• Better estimate groundwater/surface-water interactions and the formation of cool-water refugia.
• Better estimate how the distribution of aquatic plants and animals will shift in time and space.
• Better estimate how climate change and other stressors will affect salmon survival.
• Maximize realized benefits of restoration projects that enhance flows with monitoring and adaptive management.
• Better understand human water use in a changing climate.
• Determine best approaches to meet future human water needs that minimize instream impacts.

¹ Isaak, D. J., C. H. Luce, D. L. Horan, G. L. Chandler, S. P. Wollrab, and D. E. Nagel. 2018. Global Warming of Salmon and Trout Rivers in the Northwestern U.S.: Road to Ruin or Path Through Purgatory? Transactions of the American Fisheries Society 147:566-587.