ISAB Says CSS Report Would Benefit From Additional Analysis Of Climate Change Impacts

In a recently completed review, the Independent Scientific Advisory Board (ISAB) concludes that the Comparative Survival Study (CSS) needs additional analyses to better reflect the uncertainty of climate change and other future impacts on Columbia and Snake River dam operations and survival of salmon and steelhead. The annual CSS, coordinated by the Fish Passage Center in Portland, is an important study that helps regional decision-makers answer difficult ecological questions, such as the effects of the current river environment and dam operations on the survival of salmon and steelhead.

The 11-member ISAB serves the National Marine Fisheries Service (NOAA Fisheries), Columbia River Indian Tribes, and the Council by providing independent scientific advice and recommendations regarding scientific issues that relate to the respective agencies’ fish and wildlife programs.

The ISAB regularly reviews analytical products of the Fish Passage Center, including the annual CSS reports. The current review focused on Chapter 2 of the 2019 annual report, which assesses six alternative dam-operating and river flow scenarios presented in the draft Columbia River System Operations Environmental Impact Statement, (DEIS) issued in February by the Bonneville Power Administration, U.S. Army Corps of Engineers, and Bureau of Reclamation.

The federal agencies asked the CSS scientists to evaluate the six alternatives using two specific salmon models and a recently developed Columbia River Basin flow dataset based on 80 years of flow records. The CSS scientists only modeled the potential effects of the six alternatives in the DEIS, plus a seventh developed by the CSS. The ISAB reviewed the CSS analysis, but not the federal agencies’ analysis of the alternatives in the DEIS.

The ISAB scientists commented that the models and historical flow data used by the CSS, while valuable, did not evaluate potential impacts of climate change on future flows and environmental conditions or capture variation in ocean survival of salmon, a caution also noted by the CSS authors. The CSS report could be improved, however, with a deeper analysis of why the models produced the results they did, according to the ISAB report.

The ISAB commented that the CSS is an important analysis to inform not only the DEIS, but also future decision-making as well. “The CSS is a long-term effort that provides information regularly and summaries annually, so its contribution will go beyond the DEIS,” ISAB Chair Stan Gregory said.

“For such an important study,” the ISAB report notes, “caveats of interpreting current findings as representing future benefits should be more fully presented in the [CSS reports]. Many environmental, climate, operational, and social factors may change. A chart listing these other factors and their impact on the results would permit a side-by-side comparison and consideration of outcomes.”