![]() Lowland salmon streams are especially vulnerable, but retreating glaciers may allow production gains in other streams. This environmental transformation will likely harm some salmon populations while benefiting others. The landscape is also changing, with melting glaciers, wetland loss, wildfires, and human development. The region is warming and experiencing drier summers and wetter autumns. tshawytscha populations have declined, raising concerns about their future resilience. We focused on the Kenai River, which supports world-famous fisheries but where Chinook Salmon O. We examined changes in climate, hydrology, land cover, salmon populations, and fisheries over the past 30–70 years in this region. Between these geographic extremes, in the Gulf of Alaska region, salmon are at historically high abundances but face an uncertain future due to rapid environmental change. Conversely, climate warming appears to be allowing salmon to expand northwards into the Arctic. face serious challenges from climate and landscape change, particularly in the southern portion of their native range. Failure to consider the geomorphic context of stream networks will hamper efforts to understand and mitigate the vulnerability of anadromous fish habitat to climate-induced hydrologic change. Our results illustrate the importance of accounting for valley and reach-scale geomorphic features in watershed assessments of climate vulnerability, especially in topographically complex regions. Estimated effects were lower for pink and chum salmon, which primarily spawn in unconfined floodplain streams. We estimated that 9-10% and 13-16% of the spawning habitat for coho salmon could be lost by the 2040s and 2080s, respectively, with losses occurring primarily in confined, higher-gradient streams that provide only moderate-quality habitat. Potential spawning habitat loss was highest for coho salmon, which spawn over a wide range of geomorphic settings, including steeper, confined stream reaches that are more susceptible to streambed scour during high flows. ![]() Watershed response diversity was mediated primarily by topographic controls on stream channel confinement, reach-scale geomorphic associations with spawning habitat preferences, and complexity in the pace and mode of geomorphic channel responses to altered flood size. ![]() Little variation among watersheds in potential spawning habitat change was explained by predicted increases in mean annual flood size. Spawning habitat responses varied widely across watersheds and among salmon species. We combined field measurements and model simulations to estimate the potential influence of future flood disturbance on geomorphic processes controlling the quality and extent of coho, chum, and pink salmon spawning habitat in over 800 southeast Alaska watersheds. Increased flood size could alter stream habitats used by Pacific salmon for reproduction, with negative consequences for the substantial economic, cultural, and ecosystem services these fish provide. In rivers supporting Pacific salmon in southeast Alaska, USA, regional trends toward a warmer, wetter climate are predicted to increase mid- and late-21st-century mean annual flood size by 17% and 28%, respectively. ![]()
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