Supporting datasets for article "Effects of climate change on stream temperature and salmonid habitats in a Cascades river basin"

Rising stream temperatures pose significant challenges to aquatic ecosystems, particularly for coldwater-adapted organisms like salmonids. This study examines the effects of climate change on stream temperatures and salmonid habitats in the Clackamas River Basin, Oregon, USA. Using spatial stream network models and CMIP6 climate projections under SSP2-4.5 and SSP5-8.5 scenarios, we project mid- (2045-2074) and late-century (2075-2100) stream temperature changes. These projections are then integrated with thermal tolerances and intrinsic habitat metrics to assess future habitat suitability for key species, including steelhead, coho, Chinook, and bull trout. Stream temperature trends from 1991–2023 reveal basin-wide warming, with high-elevation tributaries demonstrating more resilience to climate impacts while lower-elevation subwatersheds face greater vulnerability. Future projections indicate a basinwide maximum 7-day average of daily maximum stream temperature increases of 1.42°C to 2.04°C for the midcentury, and 1.84°C to 3.24°C by the end of the 21st century. These increases reduce the most thermally suitable habitats for steelhead, coho, Chinook, and bull trout by an average of 28% to 34% during the mid-century time period, and 32% to 49% by the end-of-century time period. By linking climate-driven temperature projections with habitat metrics, we identify priority subwatersheds based on projected thermal suitability where conservation efforts can maximize impact.