Effects of climate on the expression of the urban stream syndrome

Urban streams display many similar symptoms around the world, but awareness is growing that the mechanisms and severity of the symptoms differ among regions. Climate is a key contributor to these differences via: 1) variation in the initial conditions of streams across climate (and their sensitivity to urbanization), 2) interactions between climate and urbanization, and 3) indirect effects of climate on the form of urbanization or management via effects on human behaviors. We discuss the direct and indirect pathways by which climate shapes the structure and function of urban streams and how differences in climate affect how the urban stream syndrome is manifested. For some symptoms, such as stream flashiness, climate can affect the direction and magnitude of response, whereas for others, such as losses of sensitive taxa, climate can affect the magnitude of the response. Mechanisms linking urbanization with ecological degradation, even when responses are similar, can differ among climates. Limited research has been done on the role of climate in stream response to urbanization. Controlled, large-scale studies are needed to address this issue, particularly because climate may covary with types of infrastructure and technological capabilities across the globe. Understanding the linkages between climate and urban stream ecosystems will improve our theoretical understanding of urban streams and our ability to implement tailored and regionally sensitive management strategies.