Climate Change and UHI in Hong Kong
- Marco Mak
- Jun 12, 2015
- 14 min read
Evaluate the human adaptation to intensifying UHI in Hong Kong
By Marco Mak
12 Jun 2015
1. Introduction
In the 20th century, climate change has become one of the most serious environmental issues that has threatened the fragile ecosystem and drastically affected human societies. With rapid development and urbanization, different problems aroused in human settlements in developing and developed countries. In megacities, Urban Heat Island (UHI) effect has become problematic in densely built urban area. By 2050, the world is expected to have 6 billion urban populations due to rapid urbanization. Cities are prone to climate change from greenhouse gas induced radiative forcing and localized effect of UHI. The UHI effect is expected to intensify with the climate change. (McCarthy et al. 2010)
This essay aims at evaluating the human adaptation for intensified Urban Heat Island Effect caused by climate change in Hong Kong from 1997 to present. The time scale of 1997 to present is chosen because the current Hong Kong SAR government started to govern Hong Kong since the handover of Hong Kong to China in 1997. To tackle this question, the UHI effect and climate change in Hong Kong will be examined. Related human adaptations for intensified UHI effect caused by climate change will be analyzed and discussed. Various related literature from Hong Kong and around the world will be studied and the situation in Hong Kong will be compared with other cities with similar scale. Further suggestions will be made regarding human adaptation measures for UHI in Hong Kong.
2. Urban Heat Island Effect and Climate Change in the context of Hong Kong
Urban heat island effect mechanism
According to EPA (2008), there are 2 kinds of UHI effects, namely Surface Urban Heat Islands and Atmospheric Urban Heat Islands. Surface Urban Heat Island refers to a higher surface temperature of urban area than rural area, whilst Atmospheric Urban Heat Island refers to warmer air in urban area compared to cooler air in rural area.
There are some major human and natural factors accounting for the occurrence of the UHI effect. The human factors are as follows (EPA 2008).
Properties of urban materials: Urban built area usually has lower albedo surface, meaning that urban area reflects less and absorb more heat. Also, urban materials have a higher heat capacity than rural area. More heat can be stored in urban buildings than rural area, resulting in UHI.
Lack of vegetation: The lack of vegetation in urban area decreases evapotranspiration and causes the temperature to increase.
Urban geometry: The rugged surface of buildings in build-up urban area increases the surface area to absorb heat. The spacing of tall buildings can also obstruct wind and hinder atmospheric mixing, resulting in higher temperature.
Anthropogenic heat emission: In urban area, human activities like air-conditioning, transportation and industrial processes produce heat and can warm up urban area. It contributes to UHI effect.
Apart from human factors, there are 2 natural factors that contribute to UHI (EPA 2008).
Weather: With clear sky and calm wind, the condition for the formation of UHI is optimal. During the occurrence of a heat wave, UHI can be intensified.
Geographic location: Climate and topography is determined by a city’s geographical location. Temperature of a coastal city can be regulated by large body of seawater and sea breeze. Mountains near cities can alternate the wind direction and affect the formation of UHI.
These factors caused the higher surface temperature in urban area than surrounding rural area, creating UHI in the urban area, which can be observed in isothermal map. An isothermal map would show that a “heat island” is above the urban area while the rural area remains cool, as seen in figure 1 (EPA 2008). Oke (1973) found that population size of a city is positively correlated to the UHI intensity.
Figure 1: An isothermal map showing an Atmospheric Nighttime Urban Heat Island (EPA, 2008)
Urban Heat Island in Hong Kong
UHI has been a serious environmental issue in Hong Kong. The built-up area of Hong Kong has many favorable factors contributing to the formation of UHI. For the human factors, Hong Kong has been dubbed the “concrete jungle” which concrete and glass-walled buildings are built closely together. In the inner city of Hong Kong, worn-down buildings with decaying façade are packed together with narrow alleys and dark-colored rooftop. This kind of urban environment is optimal for absorbing heat and creating UHI. Also, bad urban design is a main cause for UHI. Residential estates with large podium footprint that takes up 100% of site area are erected in newer developed area. Along with high-rise redeveloped residential buildings in the gentrified inner city, UHI has been intensified as wind movement is blocked at ground level, resulting in wall effect (figure 2) and UHI effect. Moreover, the lack of greenery in the urban areas helped to cause the UHI effect. With a crowded living environment, households in Hong Kong turn on their air-conditioning throughout summer. The heat exhaust of the air-conditioning contributes to the formation of UHI.
Figure 2: Examples of wall effect caused by high-rise buildings blocking the onshore wind. (Wong et al 2011)
As for natural factors, although Hong Kong is a coastal city, has a mountainous northern area blocking the northern monsoon in the winter. This traps the urban heat in the winter months, creating UHI. In summer month, the mountains trap moisture from southern monsoon, generating hot wet weather and UHI and causing discomfort for city dwellers.
There have been researches of the intensity of UHI in Hong Kong. In 2004, the UHI value in urban areas in Kowloon Peninsula and northern Hong Kong Island was 2.17°C (Green Power 2012). In 2007, researchers measured that the average temperature difference between rural and urban areas in winter nights was 7°C - 8°C, with a maximum difference up to 12°C. For summer nights, the difference was 5°C - 6°C (Green Power 2012). In 2012, researchers measured 3°C – 4.7°C differences between city centers and weather stations that are located away from urban areas (Green Power 2012). These reveal that there is significant UHI effect in urban Hong Kong that can be observed and measured. Although these researches are not homogenous, it can still present a general finding of the presence of UHI in urban Hong Kong in the time series of 2004-2012.
Figure 3: Average Temperature Profile (ATP) of Kowloon in 2012 (Green Power 2012)
Figure 4: Average Temperature Profile (ATP) of Tuen Mun in 2011 (Green Power 2012)
The effect of UHI in urban Hong Kong can be observed on an Average Temperature Profile (ATP) in figure 3 and 4. Green Power (2012) made several ATPs: one in Kowloon Peninsula, the urban area of Hong Kong, where the building density is high; another in Tuen Mun, a new town with high density residential and industrial zones. The ATPs show that there were significant UHI effects, which the center of the urban area was a few degrees higher than edge of the urban area. A few UHI “summits” are visible in the ATP. Also, the ATPs exhibit the cooling effects of some urban features. There is a drop in the ATP in Kowloon Park in figure 2 and a drop in ATP when it intersects the Tuen Mun River Channel. This shows that urban green area and river or stream flowing through an urban area can have a cooling effect on the surroundings.
Intensifying UHI in Hong Kong
It is very likely that climate change can strengthen UHI in Hong Kong. According to IPCC AR5 (2014), climate change can influence localized microclimate and strengthen the UHI by altering the natural factors that contribute to UHI. Also, the increase of frequency of hot days and hot spells caused by climate change can enhance the effect of UHI (IPCC 2014). For instance, climate change in New York City had extended heat wave and enhanced the UHI condition (ibid).
Hong Kong will be facing different challenges from climate change that would probably intensify the UHI effect. Welford (2008) pointed out that Hong Kong would have to adapt to the following climate change challenges: extreme weather, flooding, heat waves, health impacts and threatened ecosystem service. Within these challenges, extreme weather of more hot days and heat waves contribute to UHI. The increase of intensity of UHI can cause health issues like heat stroke and can even cause death for urban dwellers (EPA 2008). This shows that Hong Kong would have to take actions to adapt to these climate change challenges.
3. Analysis and Discussions of Adaptations to UHI in Hong Kong
In this part of the essay, the current adaptations to UHI and their issues in Hong Kong will be analyzed. The adaptations to UHI in Hong Kong will be discussed regarding Hong Kong’s vulnerability, resilience and adaptive capacity to climate change intensified UHI. At last, the relationship of adaptation and mitigation of UHI will be explored.
Current adaptations
Hong Kong as an international city has some initiatives to adapt to the impacts of climate change. To adapt to the intensifying UHI effect, the Environmental Protection Department of Hong Kong (EPD) suggested 3 adaptation “options”: regularly updating the Urban Climatic Map (UCM), promoting green roofs and promoting cool roofs (EPD 2010).
Regularly updating the UCM
The Planning Department of Hong Kong commissioned the Urban Climatic Map and Standards for Wind Environment - Feasibility Study in 2006. It divides Hong Kong into 5 Urban Climatic Planning Zone according to their sensibility to thermal comfort determined by factors like wind direction, UHI effect and wall effect. The UCM provides strategic framework and information for better urban planning (CUHK et al 2006). EPD suggested updating the UCM regularly every 4-5 years.
Promoting green roofs
The Architectural Services Department commissioned a study of the application of green roofs in Hong Kong in 2007. In 2010, EPD suggested the government to actively encourage the private sector to adopt green roofs, and maximize the use of green roofs in new urban development and urban renewals. In 2013, the Hong Kong Government set up the “Steering Committee on the Promotion of Green Buildings”. It aims at leading and coordinating the work of green building among governmental departments (Greenpeace 2015).
Promoting cool roofs
EPD suggested that the government should encourage adopting cool roofs when green roofs are not suitable. Also, the government can encourage cool roofs for public transportation (EPD 2010).
Apart from the above, greening the urban area is key to alleviate and adapt to UHI. Having greenery in urban area can effectively lower the surface and air temperature. A minimum of 2 square meters open space per person is advised in The Hong Kong Planning Standards and Guidelines by the Planning Department (Jim 2002). However, it is criticized that many old districts barely met the minimum standard (ibid).
Issues of current adaptations
Economic issue: “Real estate hegemony”
The urban development in Hong Kong is controlled by the “real estate hegemony”. Having a laissez-faire market economy, the “real estate hegemony” flourished and gained control of the urban development in Hong Kong. With limited flat land, the real estate developers design the residential buildings with high density and limited green space to maximize their profit. This utilitarian approach in urban development cause difficulties in climate change adaptation as the “real estate hegemony” aims at profit-maximization rather than environmental protection. The “real estate hegemony” has little intention to adopt green roofs in their buildings if there is no incentive.
Technological issue: Green roof technology
The adaptation of installing green roofs can be hindered by technological problems. In many cases in urban renewal, structurally decayed inner city buildings are not suitable for green roofs as the buildings may not be able to support the green roofs. Better technology is needed solve the problem of installing green roofs in inner city area.
Governance: Collusion between the government and developers
In Hong Kong, the collusion between the government and developers hindered the adaptation to UHI. The Hong Kong government had implemented policies that are favorable to developers. For instance, government implemented “incentive planning” to allow 10% more plot-ratio if the building is a “green building” (Greenpeace 2015). However, Greenpeace (2015) criticized that the criteria of “green building” is too low. Many of the building did not even attain the “BEAM Plus” bronze rating. This policy could not alleviate the problem of UHI and had even become a mean for the developers to earn more profit. This shows that the collusion between the government and developers has been a hurdle for adaptation to UHI in Hong Kong.
Governance: Ineffectiveness of the Town Planning Board
Moreover, the collusion between the government and developers had made the Town Planning Board (TPB) of Hong Kong a “rubber stamp” (Land Justice League 2015). The TPB board members are all appointed by the Chief Executive of Hong Kong[1]. Conflict of interest of board members with the developers is common in the TPB. With limited public participation in the TPB, the TPB can easily approve town plans that are favorable for developers rather than public interest. The policing power of public authority is lacking for the TPB. This hinders the public involvement in adaptation to UHI through urban planning process.
Governance: Compartmentalization
The rigid governmental compartmentalization had affected the efficiency and effectiveness of employing the adaptation measure of greening. 6 out of 16 governmental bureaux and 15 out of 38 departments have been working on greening (Jim 2002). Jim (2002) argued that the departments are operating in isolation, which they do not exchange information often, are lacking of understanding at high-level officials and of leadership in urban greening. This governmental compartmentalization is common in Hong Kong and is unfavorable for the greening process for Hong Kong to adapt to UHI.
Adaptation as mitigation
The adaptation measure of greening can be mitigation to climate change. As UHI intensifies, the usage of air-conditioning would increase to lower the room temperature. Nevertheless, this would increase the electricity consumption and carbon emission. The heat exhaust from the air conditioning would contribute to the intensification of UHI, resulting in a “vicious cycle”. With greening, the urban temperature can be lowered and the usage of air-conditioning can be reduced. This can alleviate the negative effect of the “vicious cycle”. Greening helps lower carbon emission and increases adsorption of carbon in urban area, serving as mitigation to climate change.
Resilience, Vulnerability and Adaptive Capacity
The definition of resilience, vulnerability and adaptive capacity has been a hot topic in epistemological debate. In this section, I will adopt the definitions from Miler et al (2010) and Gallopín (2007). Resilience can be referred to the “ability of a system to absorb shocks, to avoid crossing a threshold into an alternate and possibly irreversible new state, and to regenerate after disturbance” (Miller et al 2010, 3). Vulnerability can be viewed as “a condition, encompassing characteristics of exposure, susceptibility, and coping capacity, shaped by dynamic historical processes, differential entitlements, political economy, and power relations, rather than as a direct outcome of a perturbation or stress” (Miller et al 2010, 4). Adaptive Capacity refers to the “ability of a system to adjust to climate change, to moderate potential damages, to take advantage of opportunities, or to cope with the consequences” (Gallopín 2007).
Resilience
Since the concept of resilience originated from natural science, I would like to analysis and discuss about resilience of urban Hong Kong in terms of its physical urban space. The resilience of urban Hong Kong is low mainly due to the lack of greenery in the urban area. As mentioned above, Hong Kong is a “concrete jungle” with UHI effect and walled effect. The small number of greenery like parks and small open spaces has limited capacity to absorb shock from possible extreme weather events caused by climate change. It is very likely for the concrete building to absorb a huge amount of heat during extreme weather events like heat waves. This would cause serious health issues and deaths when the urban area becomes too hot for the vulnerable people. In fact, this had happened on July 28, 2014. On that day with Very Hot Weather Warning active, 1952 elderly seek assistance and 98 were taken to the hospital due to high heat (RTHK 2014). This shows that the system can easily go over the tipping point.
Although the urban area can get uncomfortably hot, many places in urban Hong Kong like apartments and shopping malls are equipped with air-conditioning. People can get into shopping malls or go home to get immediate relief when heat wave hits. Thus, this technological system (of air-conditioning) can absorb some shock in short run.
Vulnerability
The urban poor and the elderly are among all the most vulnerable to the impact of intensifying UHI effect in Hong Kong. Most of the urban poor live in the inner city area, which is densely built and has a crowded living environment. Hong Kong, being one of the cities with highest rent, many urban poor cannot afford proper accommodation and have to live in jam-packed environment. Many of them have to rent subdivided flats, which are smaller flats with a size of 10 square meters divided from a larger flat with wooden planks and often does not have ventilation (see figure 5). Some are “cage people” who can only afford a cage in the inner city (see figure 5). Some live in illegal structures that are built on rooftops of the inner city. It is very often that there is no air-conditioning in these poor living spaces and room temperature can reach to 40°C in summer time without ventilation. Even if there were air-conditioning, they would not use it to avoid high utility bills (EPA 2008). The urban poor have to endure the high heat in their living place and can very easily get sick. When extreme hot weather occurs, the ill urban poor can easily back up the hospitals and add stress to the public health system. Thus, the urban poor are vulnerable to the intensifying UHI effect.
Figure 5: Left photo shows a family living in a subdivided flat. Right photo shows the living conditions of “cage people”.
(Photo sources: Photoblog.hk; hk.apple.nextmedia.com)
As for the elderly, a few factors contribute to their vulnerability. Some low income elderly live in the poor living environment mentioned above and can get ill easily. Also, social isolation can increase their vulnerability (EPA 2008). Many of the elderly do not have family or friends or neighbors to check on them, leaving them stranded during hot days. Therefore, elderly are vulnerable to the intensifying UHI effect as well.
Adaptive capacity
The adaptive capacity of Hong Kong to the intensifying UHI is low. Although Hong Kong has a large amount of recourses to deal with UHI effect, the urban governance of Hong Kong has been incremental rather than transformative. The Hong Kong government’s lack of legitimacy[2] had led to a form of conservative governance. Innovation is discouraged and government officials tend to maintain the essence of the system. No drastic, comprehensive and transformative changes to the system have been introduced. For instance, only green building features are being promoted as adaptation measures but it lacks a long-term citywide green plan. The government failed to make fundamental changes to remove the “real estate hegemony” that has been controlling the urban development as the government is benefited from this existing system. Since it is difficult for the existing to change, the ability of the public and private sector to adjust for adaptation to UHI is low. Since the adaptive capacity of public and private sector remains low, it left the civic sector to lead the society to adapt to the intensifying UHI.
4. Suggestions and Conclusion
In order to adapt to the intensifying UHI, the government of Hong Kong should move from incremental adaptation to transformative adaptation. The governance issues have to be dealt with and the government needs to be dedicated to bring about fundamental changes in the urban governance system. Innovative and radical changes have to be made to rebuild resilience in urban Hong Kong. Some adaptation measures are proposed below:
Current institutional set-up has to be modified. Collusion of the government and developers has to be stopped. The TPB needs to be reformed to include public participation.
The Planning Department should adopt better urban design with more open space and reducing building footprints in zoning and future new towns. New urban planning zone of “amenity zone” can be introduced for urban greening (Jim 2002). Public participation should be guaranteed.
Apart from green roofs and cool roofs, urban agriculture can be promoted. The civic sector can engage in urban agriculture and set up community roof top farms and get the urban poor involved. This can alleviate the effect of UHI, reduce carbon emission, increase social cohesion and improve urban food security.
As Hong Kong grows and society advances, climate change has intensified the UHI effect, causing health issues in the city. Poor governance and other factors made the human adaptation measures ineffective and uncreative. With a better coordination between the public, private and civic sector, human adaptation measures to UHI can then be effective.
Reference
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