The Cooling Effect of an Urban River and Its Interaction with the Littoral Built Environment in Mitigating Heat Stress: A Mobile Measurement Study

Abstract

Rivers within urban areas could influence the thermal environment by modifying air temperature (AT) and relative humidity (RH). To further explore the cooling effect of a large river on surrounding urban areas, we conducted mobile measurements near the Yangtze River in Wuhan during a hot and humid summer day. This research examined the river cooling effect, determined the thresholds of the cooling and humidifying distance using a third-order polynomial method, assessed littoral heat stress at the pedestrian level and investigated the impact of the littoral built environment using stepwise regression analysis. The results revealed that (1) the cooling and humidifying effect of the river was up to 3.55 °C, 1741 m and 17.25%, 1369 m in the daytime, which was much greater than that at night; (2) the river significantly mitigated pedestrian heat stress within 1200 m from the riverbank in the daytime, but showed a weak negative effect at night; (3) the built environment has a significant impact on the littoral areas, e.g., urban greening during the daytime and building morphology at night. The findings of this study provide empirical evidence for the cooling effect of a large river in urban areas and further support climate-sensitive planning and design for our thermal environment.