Mechanistic Simulations Suggest Riparian Restoration Can Partly Counteract Climate Impacts to Juvenile Salmon.

Climate change is reducing summertime water availability and elevating water temperature, placing human consumptive needs in competition with needs of coldwater fishes. We worked with natural resource managers in the Snoqualmie River (Washington, USA) to develop riparian management scenarios, and used a process‐based modeling system to examine how a threatened population of Chinook salmon (Oncorhynchus tschawytscha) may respond to climate change and whether riparian restoration could reduce climate effects. Linking models of global climate, regional hydrology, water temperature, and fish, we projected that streams would become warmer year‐round and drier during summer, further stressing salmon. Climate change accelerated egg emergence, increased juvenile growth and survival, and accelerated outmigration of sub‐yearling migrants. Growth was depressed for salmon remaining instream during summer (potential yearling migrants). Riparian restoration counteracted ~10% of summer increases in water temperature, and affected salmon similarly regardless of whether riparian buffers were partially or fully restored, whereas riparian degradation further warmed streams. Riparian restoration fully mitigated climate change effects on potential yearling migrant size, but only minimally affected sub‐yearling migrants (assessment metrics changed <2%). Our results will be useful for watershed managers in aligning priorities for fish and humans and our framework can be applied elsewhere. Research Impact Statement: Coupling a hydroclimatic and a fish model enabled us to mechanistically evaluate when and where riparian restoration was most likely to benefit a threatened salmon population in a future climate. [ABSTRACT FROM AUTHOR]