Identifying the impacts of urbanization and extreme flows on river water temperatures in headwater catchments

Urbanization and extreme flows are altering stream temperature dynamics, yet our understanding of the impact of urbanization and extreme flows on stream temperature is limited. We deployed 27 water temperature loggers in three headwater catchments over three summers. We categorized flow as low, high, or average and calculated daily water temperature anomalies. Comparing Z scores between flow conditions revealed the impact of extreme events on water temperature. We used multiple linear regressions to identify landscape predictors of water temperature. We found during low flows stream temperatures were significantly warmer. Additionally, urban landscape predictors were linked to reduced warming during low flows. Our study highlights that low flows increase extreme water temperature events; however, this effect was less pronounced in more urbanized sites. High flows did not significantly affect water temperature anomalies. These results underscore the vulnerability of rivers to extreme temperatures during low flows; however, landscape may help mitigate these effects.