A synoptic climatology of urban heat island intensity in Hong Kong

Hong Kong is a densely populated Asian city with a monsoon-influenced humid subtropical climate that can experience a pronounced urban heat island (UHI). This study has investigated the influence of synoptic weather patterns on the intensity of the UHI in Hong Kong. Synoptic weather patterns were classified using multivariate statistical techniques principal component analysis and cluster analysis to classify days over a thirty year period into meteorologically homogeneous synoptic categories. Six synoptic categories were identified.

Maximum UHI intensity, ranging from 3-6 °C during the night and 0-3 °C during the day, was found to be associated with a high pressure system located over NW China resulting in light north easterly winds and minimal cloud cover. These conditions tend to occur during the winter months when Hong Kong is under the influence of the winter monsoon. During the summer when Hong Kong is dominated by low pressure systems situated in the South China Sea and southerly flows associated with the summer monsoon the urban heat island is not so dominant during the day however it was found to be in the range of 1-3 °C during the night adding a further burden to the already hot, oppressive nights experienced during Hong Kong summers.