A Numerical Study of Urban Heat Island Characteristics and Local Circulation in Hong Kong Using a Multilayer Urban Parameterization

Hong Kong, a subtropical coastal city, is located at the rapid urbanization area in PRD (Pearl River Delta) region. Urban heat island phenomenon and high frequency of ozone episode occurrence are fund in Hong Kong in the past years. In the past decades, many urban canopy models (UCM) have been developed, which are capable of describing the surface temperature or energy budget and of providing strategies to mitigate the urban heat island effect. To evaluate UHI and the effect of urbanization on the regional climate and local circulation of Hong Kong, the Weather Research and Forecasting mesoscale model (WRF) coupled to a multilayer urban canopy model (BEP/BEM) was used. To better represent the city morphology, gridded building information is assimilated in Kowloon Peninsula and land cover and land use (LCLU) data is modified. Specifically we focused on 3-days period from September 15th to 17th, 2012 for which detailed street level temperature and other meteorological data were available. Surface air temperature, absolute humidity and wind data from 17 weather stations were used to evaluate the model performance. The use of WRF-BEP/BEM model significantly improved simulation results on 2m diurnal air temperature profile, nocturnal urban heat island phenomenon, time and horizontal and vertical development of sea breeze and diurnal rotation of wind profile. Results show that with the inclusion of detailed building and gridded information in the coastal and central area of Kowloon peninsula significantly improves the prediction of near surface air temperature, water vapour maxing ratio, wind speed and land sea breeze circulation, which are assessed with respect to a simplified urban morphology representation. The thermal and drag effects of buildings with maximum mean height in the dense area of Kowloon peninsula are also investigated. The onset of anthropogenic heat clearly affect the onset time and the duration of the sea breeze.