Impact of blue space geometry on urban heat island mitigation

A growing body of literature recognises the importance of nature-based solutions, in providing resilience to the effects of climate change by mitigating urban heat islands. However, a knowledge gap exists regarding the contribution of blue spaces to the urban environment. Recent evidence suggests that blue spaces within urban canyons can promote pollutant removal via the vertical transport of air under certain conditions, but this is inconclusive. Using a numerical solver that accounts for evaporation effects, we investigate the influence of blue space size and shape on the in-canyon flow structure, temperature, and water vapour distribution. Simulations were performed for waterbodies of varying size and shape at different temperatures compared to the surrounding air. Results suggest that inadequately sized warmer waterbodies are unable to promote sufficient vertical transport for pollutant removal, leading to overturning and increased temperature and humidity levels at pedestrian level, thereby worsening environmental conditions and increasing the risk of heat-related illness and mortality. Hence, larger waterbodies are better suited to nocturnal transport of pollutants and accumulated warm air away from the urban surface, while smaller waterbodies are better suited to providing localised evaporative cooling. Lastly, irregular waterbodies may have a greater cooling effect across a larger area.