  |
How
is Hong Kong affected? |
| Global
Warming and Local Urbanization |
|
The
climate change in Hong Kong can be attributed to both global warming as a result
of enhanced greenhouse effect, and localized urbanization. Details of the changes
in essential meteorological parameters and potential impacts can be found below.
|
| Temperature |
|
At the Hong Kong Observatory Headquarters, temperature readings are available
for the over 120 years period from 1885 to 2007, apart from a break during the
World War II from 1940 to 1946. Analysis of the annual mean temperature data showed
that there was an average rise of 0.12¢XC per decade in that period.
|
| |
Annual mean temperature recorded at the Hong Kong Observatory Headquarters (1885-2007).
Data are not available from 1940 to 1946
|
|
In post-war years from 1947 to 2007, the average rise amounted
to 0.17¢XC per decade. The warming at the Hong Kong Observatory Headquarters has
become significantly faster in the period 1989 to 2007, at a rate of 0.34¢XC per
decade. |
| |
Annual mean temperature recorded at the Hong Kong Observatory Headquarters (1947-2007)
|
|
Increase in annual mean temperature can be attributed to global
warming as well as local effects such as urbanization. In Hong Kong, the rates
of temperature rise at Ta Kwu Ling over the same period was
smaller than that at the Hong Kong Observatory Headquarters. The Hong Kong Observatory
Headquarters is situated at the urban areas of Kowloon whereas Ta Kwu Ling is in the rural areas of the New Territorites.
|
| |
Comparison of recent trends in annual mean temperature in Hong Kong (1989-2007)
|
|
The temperature trend at the Hong Kong Observatory Headquarters
is typically the effects of urbanization where temperatures are higher than their
rural surroundings. Temperature differences that develop between an urbanized
area and the rural landscape are in essence a result of dissimilarity in radiative
fluxes. Buildings and other concrete surfaces in the urban areas retain the heat
produced by incoming solar radiation during the day and release the heat in the
form of long-wave radiation during the night. High-rise buildings also inhibit
the transfer of long-wave radiation to the atmosphere. This results in a slower
fall of temperatures at night and a higher minimum temperature than when buildings
were absent. |
| Rainfall |
In the 61-year period after the World War II, the annual total
rainfall at the Hong Kong Observatory Headquarters has been risen at a rate of
46mm/decade, though not
statistically significant at 5% level. The annual rainfall trend is small when
compared to the year-to-year fluctuations. The strength of El-Nino Southern Oscillation
(ENSO) and the winter monsoon in the preceding winter are important factors affecting
the interannual variability of the rainfall. |
| |
Annual rainfall at the Hong
Kong Observatory Headquarters (1947-2007)
|
| The
rainfall over different regions of Hong Kong was generally on a rising trend.
The rate was higher over the urban areas than the New Territories, offshore islands
and high grounds. Ubanization is one of the possible casues 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. |
| Visibility |
|
One
visible aspect of climate change is the turbidity in the sky which more and more
local people are concerned about. It is caused by suspended particulates of one
kind or another thrown up by human activities in the city. It may be purely dust
and natural (e.g. loess from northern China). It could be particulates formed
from combustion products (e.g. vehicle exhaust, kitchens and power generattion)
through photochemical processes.
The
number of hours of reduced visibility below 8 km observed from the Hong Kong Observatory
Headquarters each year was counted, with cases of visibility impairment that was
concurrent with reports of fog, mist and rain or associated with high relative
humidity (95% or more) were excluded. The visibility observed at the Hong Kong
Observatory Headquarters from 1968 to 2007 has a deteriorating trend. Up to the
late 1980s there was no significant trend. But from then onwards, there has been
a dramtic rise in the frequency of reduced visibility. The occurrence of reduced
visibility was increased at a rate of about 580 hours per decade in the period
between 1988 and 2007 as compared with that of 53 hours per decade during 1968
to 1987.
|
| |
Annual total number of hours
with visibility at the Hong Kong
Observatory Headquarters below 8 km from
1968 to 2007
(relative humidity below 95 % and not counting rain, mist or
fog)
|
|
| Sea
Level |
|
In Hong Kong, the tide gauge stations at North Point (1954-1985) and Quarry
Bay (since 1986) have recorded the sea level of the Victoria Harbour for more
than 50 years. An analysis of the records shows that the mean sea level in the
Victoria Harbour has risen 0.13 m from 1954 to 2007, at an average rate of 2.4
mm per year. The trend was similar to that over the South China Sea as measured
from satellites using remote sensing technques from 1993 to 2005. |
| |
Annual mean sea level at North
Point/Quarry Bay (1954-2007) |
A
major impact of the mean sea-level rise in Hong Kong is an increase in sea flooding
from storm surges caused by tropical cyclones. For a rise of 0.18 m or 0.59 m
in the mean sea level and assuming no change in storm characteristics, the extreme
sea-levels in the Victoria Harbour for various return periods would become higher
as illustrated below:
|
|
|
Return
Period (years)
|
Extreme
sea-level above Principal Datum (m) |
|
Current
mean sea level
|
A
rise of 0.18 m in
mean sea level
|
A
rise of 0.59 m in
mean sea level
|
| 2 |
2.8 |
2.9 |
3.3 |
| 5 |
3.0 |
3.1 |
3.5 |
| 10 |
3.1 |
3.3 |
3.7 |
| 20 |
3.2 |
3.4 |
3.8 |
| 50 |
3.4 |
3.5 |
4.0 |
| 100 |
3.5 |
3.7 |
4.1 |
| 200 |
3.6 |
3.8
|
4.2
|
|
| Cloud
Amount |
|
An increase in cloud
amount can cause a decrease in diurnal temperature range by reducing the solar
incoming radiation during day time and trapping of long-wave radiation at night.
The diurnal temperature range has decreased since the 1950s worldwide and the
coincidental increases in total cloud cover are often cited as a likely cause
for the observed decrease in diurnal temperature range.
In
Hong Kong, cloud amount is reported in oktas hourly by trained observers at the
Hong Kong Observatory Headquarters. The daily mean cloud amount is taken as the
average value of the observed hourly cloud amount in a day. Based on these daily
mean cloud amounts, annual mean values were calculated.
The annual mean cloud amount has been increasing at a rate of 1.3% per decade
in the period 1961 to 2007. One potential cause for the increase in cloud amount
over Hong Kong could be the increase in the concentration of condensation nuclei
in the air (that favoured the formation of clouds), which is known to be associated
with urbanization. |
| |
|
Annual mean cloud amount recorded at the Hong Kong Observatory Headquarters (1961-2007)
|
| Solar
Radiation |
|
Both
the increase in the concentration of suspended particulates and the increase in
cloud amount would reduce the amount of solar radiation reaching the surface.
At King's Park, the amount of solar radiation reaching Hong Kong is recorded continuously
by thermo-electric pyranometers. Between 1964 and 2007, there has been a clear
, board falling trend. For the whole period, the annual mean daily global solar
radiation has decreased at a linear rate of 0.84 MJm-2 per decade.
|
| |
|
Annual
mean daily total global solar radiation at King's Park (1964-2007)
|
| Tropical
Cyclone |
|
In the South China
Sea, the annual number of tropical cyclones landing over the south China coast
within 300 km of Hong Kong in the past 40 years or so from 1961 to 2007 has decreased
from about 3 tropical cyclones in the 1960s to about 2.5 in the 1990s, at a rate
of about 0.18 per decade which was not statistically significant at 5 % level.
|
| |
|
Annual
number of tropical cyclone landing over the south
China coast within 300
km of Hong Kong (1961-2007)
|
| Potential
Impacts |
|
Information
on potential impacts can be found at:
 Climate
- Hong Kong (in Chinese only)
Characterizing
the Climate Change Impact in Hong Kong
Climate
Change and Its Impacts
Issues
Related to Global Warming - Myths, Realities and Warnings
On
Climate Changes Brought About by Urban Living
Long-term
Trend Analyses of Weather Stress Indices for Human (in Chinese only)
Oasis-Climate-Hong
Kong (in Chinese only)
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