Effects of Anthropogenic Heat Flux Using Different Air Conditioning Systems on the Heat Wave Events in the City of Hong Kong

Urban heat island (UHI) is generally considered to be one of the major environmental challanges to human beings due to ongoing rapid urban expansion and climate change, while few researches have focused on urban cool island (UCI). It has been investigated that UHI occurs during the night and UCI happens during the day especially under calm and cloudless days in Hong Kong, a high rise and compact city. It is found that UCI can occur in the high rise and high compact city when the anthropogenic heat is small or absent. However, during June and July, 2016, HKO (Hong Kong Observatory) station recorded the hottest temperature than the surrounding rural stations. This unusual temperature excess at HKO is of our interest here. Hence we focused on a 3-days period from July 23rd to 25th, 2016 for which detailed surface level temperature and other meteorological data were available. To evaluate UHI and the effect of anthropogenic heat flux, especially the different kinds of HVAC systems, on the regional climate and environment of Hong Kong, the Weather Research and Forecasting mesoscale model (WRF) coupled to a multilayer urban canopy model (BEP/BEM) was used. Surface air temperature, absolute humidity and wind data from 33 weather stations were used to evaluate the model performance. The detailed building information was assimilated in the urban canopy model for reasonably representing city morphology. The use of WRF-BEP/BEM model shows good agreement on 2m diurnal air temperature profile and distribution and diurnal wind profile and rotation. The thermal and drag effects of buildings with a maximum mean height in the dense area of Kowloon peninsula are also investigated. Furthermore, anthropogenic heat plays an important role on the land sea breeze circulation especially along the coastal area. The onset of anthropogenic heat clearly affects the time and the duration of the sea breeze. The inclusion of cooling tower and air cooled air systems can significantly influence the surface air temperature, with a reduction of 0.5 and 0.6K, respectively, and they can affect the dynamic of urban boundary layer.