Empirical stream thermal sensitivities cluster on the landscape according to geology and climate

Abstract

Abstract. Climate change is modifying river temperature regimes across the world. To apply management interventions in an effective and efficient fashion, it is critical to both understand the underlying processes causing stream warming and identify the streams most and least sensitive to environmental change. Empirical stream thermal sensitivity, defined as the change in water temperature with a single degree change in air temperature, is a useful tool to characterize historical stream temperature conditions and to predict how streams might respond to future climate warming. We measured air and stream temperature across the Snoqualmie and Wenatchee basins, Washington during the years 2014–2021. We used ordinary least squares regression to calculate seasonal summary metrics of thermal sensitivity and time-varying coefficient models to derive continuous estimates of thermal sensitivity for each site. We then applied classification approaches to determine unique thermal sensitivity regimes and, further, to establish a link between environmental covariates and thermal sensitivity regime. We found a diversity of thermal sensitivity responses across our basins that differed in both timing and magnitude of sensitivity. We also found that covariates describing underlying geology and snowmelt were the most important in differentiating clusters. Our findings can be used to inform strategies for river basin restoration and conservation in the context of climate change, such as identifying climate insensitive areas of the basin that should be preserved and protected.

Relationships between snowpack, low flows and stream temperature in mountain watersheds of the US west coast

“…It may be that Merced River temperature is less sensitive to air temperature since it has the highest maximum elevation of the watersheds analysed for temperature, and therefore much of its water comes directly from cold snowmelt for more of the year. This is consistent with other studies showing colder summer water temperatures in streams that are more snow-dominated compared with raindominated (McGill et al, 2023;Siegel et al, 2022) and suggests that snowpack (which is highly sensitive to climate change) may be an important regulator of stream temperatures.…”

Empirical stream thermal sensitivity cluster on the landscape according to geology and climate

“…Data availability. The data that support the findings of this study are available at https://doi.org/10.6084/m9.figshare.25336900 (McGill et al, 2024) and can be visualized at https://lmcgill. shinyapps.io/TimeVarying_AWC/ (McGill, 2024).…”