Urban design factors influencing heat island intensity in high-rise high-density environments of Hong Kong

Previous research on Urban Heat Island Intensity (UHI) in Hong Kong was limited to 4 weeks of field measurements during the summer in 3 major coastal housing estates. The current study extends this work to 6 months enveloping 3 ‘‘seasons’’ and 7 different locations within the coastal area. Variations in UHI in the range 1.3 1 to 3.4 1C were recorded. The study reveals seasonal changes are in general more influential on UHI than changes due to geographical characteristics. Among the seasonal models, the peak summer clear sky day’s daytime and nocturnal models examined separately were found to provide the clearest indicators of the impact of urban design variables on UHI with R2 value of 0.7 and 0.8, respectively. Sky view factor, surface albedo, altitude, vegetation above 1m in height, average height to floor area ratio, location quotient and proximity to sea are critical variables in mitigating both daytime and nocturnal UHI. Combining daytime and nocturnal data dilutes the impact of extreme values on UHI, by up to 50%, and is not useful for design solutions. Ideally design solutions may respond to the adverse impacts recorded in peak summer clear sky daytime at the concept design stage, and then have the design manipulated and validated for other seasons.