Riparian vegetation as a climate adaptation measure: modeling water temperature responses in an urban stream during low-flow heat periods

Stream temperature is strongly influenced by environmental factors that are increasingly altered by climate change, particularly during river heat periods (RHPs), when thermal stress intensifies. In urban streams, elevated water temperatures pose risks to both ecological conditions and water quality. Riparian vegetation represents one of the few manageable controls, as it can mitigate warming by reducing incoming solar radiation. This study investigates low-flow water temperatures in the Liesingbach river, a small- to medium-sized urban stream in Vienna. Riparian shading was quantified based on solar radiation transmission, and water temperatures were simulated using a calibrated coupled hydraulic and full energy balance model under current and future climate scenarios. The results highlight the importance of integrating thermal processes into urban river restoration. Riparian vegetation reduced peak water temperatures during critical low-flow periods and enhanced ecological resilience, although it could not fully offset long-term warming. Variations in vegetation density resulted in differences in peak temperatures of up to 4.2 °C under current conditions and 5.6 °C under future climate scenarios. Despite these cooling effects, projected temperatures remained high, underscoring the urgency of mitigation measures. The increasing importance of shading under climate change further highlights its value as an adaptation strategy. Overall, the applied modeling framework provides a practical tool for quantifying these effects and supporting urban stream management under warming conditions.