Restoring Salmon in a Changing Climate

Recovery of salmon populations listed under the Endangered Species Act is guided by watershed restoration plans, but agencies and restoration practitioners are asking whether predicted climate change effects on rivers should alter those plans or priorities. Answering this question is not straightforward, as predicted climate change effects vary among river basins, and varied life history strategies of Pacific salmon complicate the development of simple rules for modifying restoration strategies to accommodate climate change. Therefore, we developed a locally adaptable protocol for evaluating salmon restoration plans. We then mapped predicted impacts of climate change on stream flows and temperatures in the Pacific Northwest, evaluated the ability of river restoration actions to ameliorate effects of climate change, and developed a set of guiding questions for evaluating whether specific restoration actions should be either re-prioritized or re-designed to improve the likelihood of successful salmon recovery.

Predicted climate effects include changes in flow regime, changes in high flows and low flows, and increases in stream temperature. Recent flow regimes are classified as snowmelt-dominated and transitional across much of the region, but predicted future flow regimes (2070-2099) are predominantly rainfall-dominated. Summer low flows are predicted to decrease by 35-75% west of the Cascade Mountains, whereas highest monthly averaged flows are predicted to increase by 10-60% across most of the region. Stream temperatures are predicted to increase by an average of 1.5°C in most rivers by 2070-2099.

Among the common restoration actions in use, restoring floodplain connectivity and re-aggrading incised channels ameliorate both stream flow and temperature changes and increase habitat diversity, whereas restoring in-stream flows can ameliorate decreases in low flows as well as stream temperature increases. Other restoration actions (e.g., reducing sediment supply, in-stream rehabilitation) are less likely to ameliorate climate change effects.

Evaluation of restoration plans and priorities focuses on (1) local habitat factors limiting salmon recovery, (2) predicted local effects of climate change on stream flow and temperature, (3) the ability of restoration actions to ameliorate climate change effects, and (4) whether restoration actions increase habitat diversity and salmon population resilience. Answering the first question requires information from previously developed salmon recovery plans or watershed restoration plans. Our analysis of potential climate change effects and literature review of effects of restoration actions help to answer the remaining three questions. This set of questions can be applied to evaluation of restoration plans or to evaluation of individual restoration actions.