Lessons Learned from Klamath Basin Stream Temperature Studies: Drivers & Climate Change Implications

Year: 2022
Presenter/s: Eli Asarian
Symposium Session: 2022 - 08 Beyond Dam Removal: Ecological Restoration of the Klamath Basin
Topics covered: climate change, fish-cutthroat, fish-salmon, fish-steelhead, instream structure (culvert/bridge/dam), lessons learned, monitoring, riparian, stream, temperature, and wildfire


For the past few decades, Native American Tribes, federal and state agencies, non-governmental organizations, and universities have monitored water temperatures in rivers and streams throughout the Klamath Basin. Beginning in 2015 and continuing through the present, Riverbend Sciences and an assemblage of colleagues compiled and analyzed this massive dataset in a series of seven projects covering nearly every sub-basin of the Klamath (Lower Klamath, Middle Klamath, Upper Klamath, Salmon, Scott, Trinity, and South Fork Trinity), each with its own objectives. A variety of statistical methods (including generalized additive models, linear mixed models, and spatial stream network models) were used to assess relationships between water temperatures and hydroclimatic factors such as river flow, snowpack, air temperature, and wildfire smoke; evaluate long-term trends; and make climate change projections. Study sites span diverse landscapes including coastal redwood rainforests, mountain wilderness snowmelt-fed streams, intensively-farmed agricultural valleys, and prodigious springs in the semi-arid Upper Klamath Basin. In this presentation, we summarize key findings from these analyses.
Summer water temperatures (especially in July) have warmed in recent decades, coincident with climate-driven increases in air temperatures and decreases in snowpack and river flow. Water temperatures have increased most dramatically at sites that are cool during high-flow years but warm during droughts. Wildfire smoke has helped limit increases in August water temperatures, but has not affected annual maximum water temperatures because in most years fires do not start until after the hottest water temperatures have already occurred. At some sites, summer water temperatures have cooled as riparian vegetation and stream channel morphology recovered from previous disturbances including a major flood in 1997. High river flows have a greater cooling effect on water temperatures in the spring and early summer than in late summer and fall. Climate change analyses for the Salmon River sub-basin indicate that August water temperatures will warm by 1.7–3.3 °C (3.1–5.9 °F) (magnitude varies by stream reach) by the end of the 21st century (2070-2099) if global greenhouse gas emissions are not reduced substantially. Reduced emissions would limit these increases and help maintain cool water temperatures.

Insights from these analyses can inform climate-resilient restoration strategies. For example, creek mouth thermal refugia deserve special attention for habitat restoration and watershed management because they will become increasingly important as peak summer river temperatures become increasingly inhospitable to coldwater species. Similarly, dam removal would allow anadromous fish to access Upper Basin cold volcanic springs that will be more climate-resilient than Lower Basin rivers with dwindling snowpack. To counter warming trends, restorationists and regulators will need to find ways to reduce costs and accelerate implementation of complex projects like floodplain restoration that can increase thermal diversity by promoting interactions between surface water and groundwater. Decreased snow and increased rain will necessitate greater flood control capacity, increasing the risk of depleting Trinity Reservoir’s cold-water pool and releasing warm water into the Trinity River during fall salmon spawning. Retrofitting Trinity Dam to allow water releases from multiple depths would help preserve cold water and improve conditions for anadromous salmonids.