Stream Temperature Response to Increased Shading Due To Riparian Shrubification in Northern Latitudes

Abstract 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, , 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 () 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 response was greatest in streams <5 m wide, although stream orientation influences response for wider streams. The 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.