Nocturnal heat island effect in urban residential developments of Hong Kong

In hot humid climate, mitigating summer time nocturnal Urban Heat Island (UHI) effect is important in order to reduce the spaceconditioning cost. Case studies of Belchers, Wah Fu-1 and -2 reveal the maximum nocturnal UHI in the order of 1.3 8C within an estate, and 0.4 8C between estates. The variables such as surface albedo, height-to-floor area ratio, sky view factor (SVF) and altitude are capable of explaining the nocturnal UHI in the case study areas with an explanatory power of 0.8. Although, during summer, the nocturnal UHI intensity is low relative to daytime UHI, thermal distress is high in night especially in Wah Fu-1 and -2. The paper will discuss the influence of the design variables on nocturnal UHI and its significance in relation to daytime UHI in the case study areas.