Relationships among local-scale urban morphology, urban ventilation, urban heat island and outdoor thermal comfort under sea breeze influence

Many cities are facing the problem of urban heat island (UHI) and UHI mitigation is becoming crucial in urban planning and design. The reasonable wind-sensitive design may be a feasible approach to UHI mitigation and outdoor thermal comfort improvement, as cool wind (i.e. sea breeze) is a good cooling intervention. Consistent with the precinct ventilation zone scheme, this study experimentally investigated relationships among urban morphology, precinct ventilation performance, UHIs and outdoor thermal comfort in a compact high-rise gridiron precinct in the coastal Sydney, Australia. Results indicate that precinct morphological characteristics had a strong modification effect on precinct ventilation. As a result, under different combination of external meteorological conditions and precinct morphological characteristics, there was no significant difference in precinct ventilation performance (i.e. relative wind velocity ratio). The precinct ventilation performance forced by sea breeze could significantly mitigate UHIs. Meanwhile, the precinct ventilation performance forced by the sea breeze could significantly improve relative humidity which could further significantly improve outdoor thermal comfort. The street orientation was no longer a critical factor affecting precinct ventilation performance, UHIs and outdoor thermal comfort at the precinct scale. Overall, this study preliminarily revealed precinct ventilation performance and its influence on UHIs and outdoor thermal comfort. The cooling and humidifying effects of wind background cannot be ignored in microclimate studies and should be considered for microclimate regulation in urban planning and design.