River reaches with impaired riparian tree cover and channel morphology have reduced thermal resilience

This study evaluated the effects of riparian tree cover and channel morphology on the thermal regimes of 3 adjacent rivers in different years. Riparian tree cover was found to exert a strong modifying influence on stream temperature, with reduced mean maximum summer temperature at sites having greater tree cover. The effect of tree cover changed among years, such that greater cover was required to maintain a given water temperature regime in the warmer summer of 2013 than in 2014 or 2015. Water temperature was also related to mean depth in some years; shallower sites, typically associated with artificial channel widening, showed greater temperature extremes. These results suggest that the thermal resilience of modified streams can be improved by restoration of riparian tree cover and restored channel morphology. This finding is relevant to climate change proofing of temperate river channels, where cold‐water fauna are important elements of the biotic community.