Drying summers threaten western North American river ecosystems and a keystone migratory fish

Sacha W Ruzzante, Tom Gleeson , Jonathan W. Moore, Marta E. Ulaski, Todd Hatfield, Markus Schnorbus, Stephanie J. Peacock

Climate change threatens river ecosystems by altering the seasonal streamflow patterns to which aquatic species have adapted, including keystone species like Chinook salmon in western North America. Chinook salmon display diverse life-history adaptations to local hydrologic regimes, contributing to their past resilience but leaving locally adapted populations vulnerable to changing conditions. Here we show that moderate climate change will cause extreme hydrologic changes across western North America: August streamflow could halve in one quarter of the streams we studied by 2100, and one third will probably experience a 500-year return period drought by 2035. Concurrently, increasing agricultural water demand will conflict with ecological needs. Variation in Chinook migration timing across streams and populations poses diverse local challenges but also illustrates possible adaptations and species-level resilience.