Resilient cities - Hong Kong report: extreme heat

Causes of extreme heat




Not only do high-rise, high-density buildings in Hong Kong block and hinder heat release to higher atmospheres, the high heat capacity of these buildings also absorbs and stores heat energy. Furthermore, high-rise buildings reduce wind speed and slow down the cooling process within the vicinity of Hong Kong. These factors result in higher temperatures in urban areas than that of rural areas. A further impact of the high population and building density in the city is the “wall effect”. This generally refers to high density and compact building bulk affecting ventilation to residents living in the vicinity. 18 The wall effect results in heat being trapped in urban areas, leading to a hot and stifling environment.

The high electricity fees charged also mean that people are reluctant to turn on their air conditioning units, thereby further preventing cooling within a flat. A solution to this problem is public housing flats, however, available public housing flats are limited and the waiting time is often very long. On average, elderly applicants are faced with a waiting time of 2.9 years, whereas families are expected to wait for 5.5 years as of March 2019. 21

Hong Kong possesses the most expensive housing market in the world 19 and it is increasingly difficult for the elderly to find and afford acceptable living conditions due to financial constraints. In many cases, the elderly and those with low income live in small, subdivided flats. The small size of these subdivided flats, inadequate cooling mechanisms and poor ventilation systems result in the hot conditions, which is compounded by heat emitted from cooking and electrical appliances. The temperature within these subdivided flats is usually much higher than the recorded temperature outside. For example, a 100 square foot subdivided flat in Kwun Tong recorded a temperature of 35.7°C whilst the recorded temperature of the region at the time was measured to be 30.7°C by the HKO. 20

The “urbanisation effect” 17 is a broad term which encompasses many areas including human activities, land use changes, as well as dense building developments (closely related to the wall effect in Hong Kong as discussed below). A consequence of urbanisation is the creation of the Urban Heat Island effect (“UHI effect”), which describes the situation where the cooling rate in urban areas is slower than that in rural areas.

Urban Heat Island effect

Little vegetation or evaporation causes urban areas to be warmer than

the surrounding countryside. Waste heat generated by energy usage also contributes.



Residential suburban



Residential urban


Rural farmland

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