Accessibility navigation

The urban cool island phenomenon in a high-rise high-density city and its mechanisms

Yang, X., Li, Y., Luo, Z. ORCID: and Chan, P. W. (2017) The urban cool island phenomenon in a high-rise high-density city and its mechanisms. International Journal of Climatology, 37 (2). pp. 890-904. ISSN 0899-8418

Text - Accepted Version
· Please see our End User Agreement before downloading.


It is advisable to refer to the publisher's version if you intend to cite from this work. See Guidance on citing.

To link to this item DOI: 10.1002/joc.4747


The urban heat island (UHI) phenomenon has been studied extensively, but there are relatively fewer reports on the so-called urban cool island (UCI) phenomenon. We reveal here that the UCI phenomenon exists in Hong Kong during the day, and is associated with the UHI at night under all wind and cloud conditions. The possible mechanisms for the UCI phenomenon in such a high-rise compact city have been discovered using a lumped urban air temperature model. A new concept of urban cool island degree hours (UCIdh) to measure the UCI intensity and duration is proposed. Our analyses reveal that when anthropogenic heat is small or absent, a high-rise and high-density city experiences a significant daytime UCI effect. This is explained by an intensified heat storage capacity and the reduced solar radiation gain of urban surfaces. However, if anthropogenic heat in the urban area increases further, the UCI phenomenon still exists, yet UCIdh decrease dramatically in a high-rise compact city. In a low-rise, low-density city, the UCI phenomenon also occurs when there is no anthropogenic heat, but easily disappears when there is little anthropogenic heat, and the UHI phenomenon dominates. This probably explains why the UHI phenomenon is often observed, but the UCI phenomenon is rarely observed. The co-existence of urban heat/cool island phenomena implies reduction of the daily temperature range (DTR) in such cities, and its dependence on urban morphology also implies that urban morphology can be used to control the urban thermal environment.

Item Type:Article
Divisions:Science > School of the Built Environment > Urban Living group
Science > School of the Built Environment > Energy and Environmental Engineering group
ID Code:60219
Publisher:John Wiley & Sons


Downloads per month over past year

University Staff: Request a correction | Centaur Editors: Update this record

Page navigation