https://doi.org/10.1029/2025JG009465

Szeitz, Andras J.; Wallace, Cory A.; Jackson, Faye L.; Malcolm, Iain A.; Hannah, David M.; Carey, Sean K. (2026) Stream Temperature Response to Increased Shading Due To Riparian Shrubification in Northern Latitudes, Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2025JG009465

Global warming is causing rapid and profound impacts on northern ecosystems. Shifting precipitation, permafrost thaw, and rapid shrub advance into tundra environments are combining to alter stream temperature in uncertain ways. The expansion and increased abundance of shrub vegetation, termed shrubification, may moderate warming stream temperatures through greater riparian shading. However, there has been no evaluation of how shrub expansion will affect the radiative balance and subsequent stream temperature of northern streams to date. This study (a) assesses the impact of shrubification in northern latitudes on the incident shortwave and longwave radiation received by streams across a range of stream widths, orientations, gradients, and latitudes, and (b) quantifies the potential magnitude of summer stream temperature response to the altered incident radiation. The potential temperature response was assessed regionally using a metric, ??diff, that considers changing incident radiation (?????) between scenarios of three increasing riparian shrub structures and two streamflow conditions. Subsequently, a local case study was undertaken comparing an energy balance-driven equilibrium stream temperature analysis (??eq) between the shrub scenarios. Simulation results of the hourly ????? response to substantial shrubification ranged from ?250.2 to +17.1 W m?2, with a mean of ?41.6 W m?2, across all stream scenarios. The ??diff response was greatest in streams <5 m wide, although stream orientation influences ??diff response for wider streams. The ??eq analysis indicated a variable temperature response related to the progression of shrubification. These results suggest that stream temperature response to shrubification in headwater catchments may be complex and context dependent.

Climate warming has caused rapid environmental changes in northern environments. One of these changes is the increased abundance and distribution of shrub vegetation across tundra environments, a phenomenon termed “shrubification.” Shrubification has been observed to preferentially occur along streams, and previous research in temperate regions has shown that changing the streamside vegetation can have substantial impacts on stream temperature by increasing shading or allowing more light to reach the stream. This study simulates the change in shortwave and longwave radiation a range of streams would receive as shrubification progresses, and determines its potential impact on stream temperature depending on the environmental characteristics of the streams. The results show that shrubification has an effect consistent with previous studies, suggesting that increased shading may decrease the energy received by the stream, potentially reducing stream temperature by 1–2°C in small streams assuming no other changes in stream energy exchanges. It also found that the changes in heat exchange processes due to shrubification may result in stream warming or stream cooling, depending on how extensive the shrub growth is. These results indicate that the impacts of shrubification on stream temperature are complex and context dependent.

https://doi.org/10.1029/2025JG009465