Arianna C. Goodman

Stream temperature is a key performance driver for aquatic species and a direct metric of climate impacts. We adapted a stream temperature model to predict daily temperatures across the Pacific Northwest USA through 2100. Our results suggested that stream temperatures may rise by ~1°C by the 2050's and 2°C by the 2080's, with seasonal and geographic nuances. Snowmelt‐fed streams were especially likely to experience seasonal shifts in temperature patterns. We built local models for two watersheds to show how predictions can guide Pacific salmon conservation planning. In the North Santiam River, a Willamette River tributary in Oregon, we found that Chinook salmon and Steelhead spawners and eggs may face increasingly stressful conditions below large dams. Whereas above‐dam thermal habitat will remain or become suitable, suggesting the importance of maintaining dam passage. In the Wenatchee River, an upper Columbia River tributary in Washington, future temperatures may contribute to higher pre‐spawn mortality of Chinook salmon. Cooler thermal refuges may persist in glacial and snow‐influenced parts of the landscape, but reaching high‐elevation refuges will require migrating through warming rivers. It is essential to consider temperature patterns alongside other cumulative impacts throughout the salmon life cycle. Future stream temperature estimates can help anticipate climate‐driven habitat changes and support proactive conservation strategies for lotic species.

This study examined the 70‐year history of clearcutting of old‐growth forest and associated road construction, floods, landslides, large wood in rivers, and channel change in the 64 km² Lookout Creek watershed in western Oregon, where forestry practices began in 1950 and largely ceased by the 1980s. Responses differed among three zones with distinctive geomorphic processes within the watershed: a glacially sculpted zone, an earthflow‐dominated zone, and a debris slide and debris flow‐dominated zone. Watershed response to floods was more related to the timing of road construction and clearcuts, past geomorphic events, and forest dynamics than to flood magnitude. Even small (1–3 year) floods generated geomorphic responses in the period of initial road construction and logging (1950–1964) and during ongoing logging in the early part of a 30‐year period between large flood events (1966–1995). The floods of 1964/65, 15 years after the onset of logging, produced much larger geomorphic responses than the flood of record (1996), more than a decade after logging ceased. Geomorphic response was negligible for the third largest event on record (2011) during the last period (1997–2020), when former clearcuts were 20 to 70‐year‐old forest plantations. Watershed response in each of five distinct time periods depended on conditions created during prior periods in the three zones. Understanding of watershed response to forestry requires integrated observation of forestry practices, floods, landslide susceptibility, wood delivery and movement, and channel change on time scales that capture responses to past and ongoing management practices and geophysical and biological factors and events.

Periodic oscillations between El Niño and La Niña conditions in the Pacific Basin affect oceanographic and meteorological phenomena globally, with impacts on the abundance and distribution of marine species. However, El Niño effects on estuarine hydrology and tidal wetland processes have seldom been examined rigorously. We used detailed wetland elevation and local inundation data from 10 tidal wetlands located along the Pacific coast of the United States to assess changes in flooding during the 2015–2016 El Niño and to determine decadal‐scale relationships between estuarine sea‐level anomalies and Pacific Basin climate indices for this region. During the 2015–2016 El Niño all sites experienced significant increases in high‐tide water levels exceeding those predicted by astronomical tides, and increased flooding frequency during at least one of the El Niño subperiods relative to pre‐El Niño conditions. The magnitude of positive sea‐level anomalies varied by site (4–15 cm), with local hot spots of high water in southern Oregon, northern California, and Pt. Mugu lagoon in the Southern California Bight. Furthermore, over the last three decades of historic tide records, there were positive relationships between high‐tide sea‐level anomalies and equatorial Pacific Basin sea surface temperature anomalies across the region, and negative relationships with the Northern Oscillation Index. Increases of 1 °C in equatorial sea surface temperature were associated with 3–5 cm of increased high‐tide flooding at the sites. Elevated estuarine flooding associated with future El Niños could impact important tidal wetland processes and could be an additive stressor for wetlands facing accelerating sea‐level rise.