How will Hong Kong be Affected by Climate Change?

Hong Kong is a coastal port with a long coastline of approximately 730km and 260 islands. The territory consists of around 1,104 square kilometres, and less than 25% of Hong Kong’s total area is developed, resulting in heavy urban development in low lying areas and on reclaimed land. Hong Kong’s population is roughly 7 million.

 

 

 

 

 

Long Hot Summers, No Winter 

 

According to the Hong Kong Observatory, climate change in Hong Kong can be attributed to both global warming caused by increased atmospheric concentrations of greenhouse gases, and localised urbanization which leads to the formation of what is called an 'urban heat island' where temperatures are higher than their rural surroundings. Urban heat island is caused by a combination of factors including changes in surface as vegetation is replaced by concrete and tarmac, reduced air ventilation due to buildings, anthropogenic heat production and motor vehicle emissions.

 

 

 

A hotter, wetter climate, with heavier rainfall, interspersed by longer dry periods

 

The Hong Kong Observatory (2007) has made temperature projections for the 21st Century for Hong Kong by downscaling the global climate model projections of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. Key findings include:

  • Since the late 19th Century (1891-1900), annual mean temperature rose 1.5 ºC, from 22 ºC to 23.5 ºC in 10 years (1993-2002)11.
  • Annual mean temperatures are rising at 0.12 ºC per decade, with a mean 4.8 ºC temperature rise projected by 2100.
  • Very hot days (maximum temperature of 33ºC or above) in summer will roughly double, rising from 11 days to 24 days.
  • The number of hot nights (minimum temperature of 28ºC or above) will rise to 30 per year – four times the current normal level.
  • The number of cold days (minimum temperature of 12ºC or below) in winter will decrease from 21 to less than one day per year.
  • Wet times will intensify (due to an increase in rainfall) with likelihood of more frequent storms.
  • Oscillations between wet and dry will be more pronounced.
  • Sea level is rising between 2.4 and 2.7mm per year.
  • Incidences of poor visibility are increasing by 6.8% per decade.
  • Warmer, wetter and more extreme weather will put additional stress on buildings and infrastructure. Therefore, it is necessary to develop new standards of design and engineering, particularly for low lying areas. Additional design of drainage also needs to be considered.
  • According to Associate Professor Lam Ka-se of the Hong Kong Polytechnic University, if temperatures were to rise by 3°C in Hong Kong, the likelihood of an increase in the epidemic potential of malaria would rise by 18.7%.

 

 


Source: Hong Kong Observatory (2007): Temperature Projections for Hong Kong
Based on IPCC Fourth Assessment Report


Rising Temperature

Analysis of the annual mean temperature data shows that there is an average rise of 0.12±C per decade from 1885 to 2008 The rate of increase in average temperature becomes faster in the latter half of the 20th century. In post-war years from 1947 to 2008, the average rise amounts to 0.16±C per decade, accelerating to 0.27±C per decade during 1979-2008.  Such an increasing trend is in line with that observed in southern China in the last 50 years, about 0.21±C per decade.

  •  Past: Global mean temperature increased by 0.6 ± 0.2°C in the 20th century and Hong Kong’s temperature increased in line with the global warming trends.
  • Future: Hong Kong Observatory estimates that by the end of this century, annual mean temperatures will rise on average by 4.8 °C to an average of 27.8 °C1(compared to 23°C in 1990).
  • By 2100, there will be less than one cold day a year (12°C or below), meaning that for some winters, there will not be any cold days at all, and winter could disappear in Hong Kong.
 

Source: Hong Kong Observatory

 

 

 

Heavy rainfall and rainfall variability will increase  

 

 

 

 Image: Reuters/Bobby Yip

 

  • Future: The Hong Kong Observatory (2010) reports In respect of rainfall projection for Hong Kong based on results of IPCC AR4, the average annual rainfall is expected to increase by about 11% by the end of this century. In the 64-year period after the World War II (1947-2010), the annual total rainfall at the Hong Kong Observatory Headquarters has been risen to a rate of 50 mm/decade.

 

  • Heavy and prolonged rainfall may produce excess run off (rainwater that neither evaporates nor penetrates the surface to become groundwater) which will increase the risk of flooding and landslide damage. This could impact buildings and infrastructure and cause disruption to business activities.

 

Urbanization is one of the possible causes for the rainfall's increasing trend and the regional variation in Hong Kong. The higher temperature in urban areas enhances convective activities and the increase in concentration of suspended particulates from urban activities also favours the formation and development of rain-bearing clouds.

 

 
Images: www.hkss.cedd.gov.hk
 

Increasing Rainfall Variability (Causing Water Scarcity and Drought)

  • Conversely, while the annual rainfall in Hong Kong will increase, the year-to-year variability in rainfall would also increase, meaning more years with either above average or below average rainfall. In the years of low rainfall, there will be increased pressure on water resources. Currently Dongjiang River in Guangdong province supplies about 66% of Hong Kong’s fresh water. Many rivers in China face serious water shortages from increased population, urban development and large scale manufacturing, many of which are water intensive.

 

Tropical Storms

Image: Xinhua
  • The first National Assessment Report on Climate Change in China, released in December 2006, forecasts that extreme weather events and natural disasters will occur more frequently; however, the Hong Kong Observatory has stated that there is not yet a definitive answer as to whether tropical cyclone activity has increased or will increase due to global warming. In fact, the annual number of tropical cyclones landing over the south China coast within 300 km of Hong Kong has been decreasing, from about 3 in the 1960s to 2.5 in the 1990s [LEUNG et al, 2006].
  • The observed decreasing trend in the annual number of tropical cyclone, though not statistically significant, may be due to more frequent occurrences of El Nino events since the 1980s. Generally speaking, the number of tropical cyclones affecting Hong Kong is fewer in El Nino years than La Nina years.

Rising Sea Levels in Hong Kong

 

 

56 years of tide gauge records in the Victoria Harbour since 1954 demonstrate an unambiguous rise of the mean sea level during this period. There was a rapid rise of the sea level from 1990 to 1999 and a moderate decline thereafter. The trend is similar to that observed by satellite remote sensing over the South China Sea since the early 1990s and also tide gauge records at other coastal stations in the region. On average, the mean sea level in the Victoria Harbour has risen at a rate of 2.6 mm per year during the period 1954 to 2010.

  • Past: IPCC reported in 2007 that global sea level rose at an average rate of 1.8mm per year between 1961 to 2003, with a faster rate of 3.1mm per year between 1993 and 2003 [IPCC 2007]. The total sea level rise for the 20th century is estimated to be 0.17m [IPCC 2007].
  • The Hong Kong Observatory (2004) reported that sea level in Hong Kong has been rising at an average rate of 2.3mm per year over the last 50 years. This is greater than the IPCC global average, but is consistent with rises in the South China Sea.
  • Future: The IPCC’s Third Assessment Report projected that global mean sea level (“MSL”) will rise by 9-88 cm (depending on emission scenarios and climate models) by 2100, with a central value of 48 cm, which is 3 .3 times the observed rate over the twentieth century.
  • Recent research by the Institute of the Environment of the Hong Kong University of Science and Technology, Lau et al (2007) suggests that if the sea level in 2100 in Hong Kong were to rise by the mean estimation of the IPCC’s Third Assessment Report of 48cm, the flood level with a 50 year reoccurrence interval would be shortened to a return period of about 3 years and if the water level rose by the IPCC’s upper best estimate value of 88cm the 50 year event would have a annual occurrence.
  • Storm surge (occurs when high winds pushing on the ocean and low pressure at the centre of the storm cause water to pile up higher than the ordinary sea level) has occurred in Hong Kong with typhoons in 1937 and Typhoon Wanda in 1962. In 2001, flooding due to storm surge occurred in the New Territories and Tai O Lantau during Typhoon Utor. Most storm surges have been a height of 0.5 to 1.0 metres. In extreme conditions, the water level could exceed the tide level by more than three metres, bringing sea flooding to coastal low lying areas.
  • Adaptation: The Hong Kong Observatory states that the effects of storm surges and long term sea level rise has already been taken into consideration in the design of coastal projects [HKO, 2004].
  • The Institute of the Environment at the Hong Kong University of Science and Technology, Lau et al (2007) state that it is important to plan for future sea level rises but the risks from sea level rise will always fall to current local coastal users. Often local users are more worried about seemingly more immediate threats such as erosion, land subsidence and tropical storms, separate from any concerns about climate change and associated sea level rise [Darwin 2001, ABI 2006]. It is very important that these people realize that sea level change will influence the factors that they are already concerned about and it must be combated in combination with these other factors.

 

Hong Kong is somewhat fortunate in possessing a mainly cliffed coastal topography which makes it less susceptible to some of the possible consequences of sea level rise. However, low lying areas in the Territory are likely to experience increased drainage problems. This is especially true for all areas that have storm runoff outlets and other types of outlets at or near present sea level.

 

 

Mai Po wetland is of special interest because of its ecological value. A rise in sea level could drastically reduce the area of this wetland resulting in a compression of the current ecological zones and a change of ecosystem dynamics in this area. Other areas of ecological value that may be impacted by sea level rise are Hong Kong's coral reefs. These reefs are presently growing at their thermal limit. In this respect increases in sea surface temperatures may actually enhance their rate of growth if water quality is maintained. However what is uncertain is whether the rate of coral reef growth can keep up with the rate of sea level rise. Also if there is an increase in the amount of incoming ultra-violet radiation due to changes in atmospheric composition the possibility of coral bleaching exists which may result in some die back in the reefs. An elevated sea level may also hold implications for coastal erosion and sediment transport patterns. (Source: Glenn McGregor, Department of Geography, Hong Kong Baptist College)

 

 
image: www.drmartinwilliams.com

 

Flooding in Pearl River Delta

  • Rising sea levels are a matter of great concern particularly for the PRD, where both the physical geography (the Southern part of the delta lies between -0.3m to 0.4m relative to mean sea level) and the urban development of the region render it extremely vulnerable. The rate and amount of sea level rise is the subject of some dispute in the scientific literature. Some scientists predict that it will rise 30cm by 2030 [HUANG et al, 2004]. However, China's National Assessment Report predicts a much more conservative rise of 1 to 6 cm by 2030.
  • Civic Exchange's report the Impacts of Climate Change in Hong Kong and the Pearl River Delta (2006) confirms a sea level rise of 30cm by 2030, but states that the expected sea level rise of 30 cm does not reveal the true level of the risk: raising the mean sea level by 30 cm dramatically increases the effect of storm surge. The result will be that many existing storm defenses are overtopped with increasing frequency. Existing coastal and river defenses built to protect low-lying areas of the Greater PRD will be inadequate if storm surges increase in height and major flooding incidents will occur more frequently. The PRDis southern China's manufacturing and trade centre and the knock-on effects of such flooding would be felt globally, and would quickly lead to a shutdown in key industries and trade across the delta and in Hong Kong.
  • A report by the Guangdong Meteorological Bureau in 2007 noted that more than 1,150 sq km would be inundated along China's coastline if the sea level were to rise by 30cm. If the pace picks up, the time would be shortened. In a worst case scenario, the sea level would rise 30 cm in the coming 20 to 50 years. The report noted that about 13% of the land in the PRD was below sea level and another 23.8% less than 40 cm above sea level. Thus, both the physical geography (the southern part of the PRD lies between -0.3m to 0.4m relative to mean sea level) and the urban development of the region render it extremely vulnerable.

Impact to Human Health

  • The fourth IPCC report indicates that climate change will contribute to an increased incidence of diseases and premature deaths globally through its effects on weather patterns and negative effects on food production, air and water quality. Very hot weather can de deadly and an increase in the severity of heat waves is likely to increase (predominantly cardio-respiratory) illness and mortality; and that by 2050 there will be 3.6 to 7.1 times more heat related deaths in that city.
  • According to Associate Professor Lam Ka-se of the Hong Kong Polytechnic University, if temperatures were to rise by 3°C in Hong Kong, the likelihood of an increase in the epidemic potential of malaria would rise by 18.7%.

 

Malaria
Temperature increase
Increase of Epidemic potential
1°C
6.7%
2°C
13.0%
3°C
18.7%

 

Source: LAM Ka-se (Associate Professor, Civil & Structural Engineering,
The Hong Kong Polytechnic University, ICCC Presentation, 2007 May)

 

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