-
journal of Health Science
Vol. 9 No.1 January - March 2000
Original Article
Urban Heat Island : Thermal Pollution
and Climate Change in Bangkok
Jariya Boonjawat*
Kiyoshi Niitsu**
Sachio Kubo** *
'Southesst ASia START Regional Center, c/o Environmental Research Institute. ChulaJongkorn University. Bangkok
10330. Thailand. e-mail [email protected]
·'Japan Science and Technology Corporation. Keio University
5322 Endo. Fujisaw8. Kanagawa. 252-8520 Japan. e-mail [email protected]
'''Keio University, 5322 Endo. Fufisawa Kanagawa. 252-8520 Japan. e-mail [email protected]
! Abstract:
An urban heat island (UHI) is a phenomenon where temperatures in the city are higher
than that of the outlying suburban areas. In order to study such effect in Bangkok, three
measurement systems were employed to assess heat islands, land use/land cover and anthropo ­
genic heat discharge. A network of 7 automated ground-base monitoring stations was estab­
lished for continuous observations providing so-minute interval weather data Satellite imag­
ery data from NOAA, Landsat TM thermal bands, maps and Geographic Information System
(GIS) data were used for analyzing the spatial structure of land use and land cover. On the
other hand the heat, discharged from various land covers in and around Chulalongkom Univer­
sity, was measured by a Thermography System. Throughout the 15 days in February 1998,
diurnal variations of heat island intensity profiles had been observed. The onset of an urban
heat island, defining as the temperature difference between Chulalongkorn University (city
center) and Asian Institute of Technology (suburban), became evident after sunset and a maxi­
mum of 3.5°C was reported during 13.00-7.00 am. The heat isl and intensity decreased markedIy
to - 1. 5°C in the afternoon. Sea breeze and sol ar radi ation collectively pIayed major roles. In
addition. large trees in the city campus provided a cooling effect at 20-01 level down to ground­
base temperature at t.50 m level. Sea breeze from the south direction could decrease the air
temperature in the southern part of Bangkok.
Introduction
An urban heat island (UHI) is a phenom­
enon where temperatures in a city are higher than
that of suburban areas ou tside the city. Most stud­
ies on Ul Il have been conducted in high-and mid­
latitude cities. This study shows that the urban heal
-
-
phenomena can also be observed in Bangkok.
There are several major causes that bring about
an urban heat island, which is a type of man-made
pollution , a thermal pollution:
(1) land cover change: a d ecrease of veg­
etated area and open water in particular;
Urban Heat Island: Thermal Pollution and Climate Change in Bangkok
(2) building density and patterns: reflection
ogy, Ladkrabang (KMlTL); King Mongkut's Uni­
of heat waves between walls, or/and between
versity of Technology, Tho nbu r i (KMUTT);
ground and walls increases solar heat absorption;
Mahidol University, Salaya Campus (MU); and
(3) anthropologic heat release from human
Southeast Asian Fisheries Development Center
activities;
(SEAFDEC). For vertical temperature profiles, bal­
(4) wind barrier: tall buildings block wind
loons equipped with temperature and humidity
sensors were used at CU- Stadium, AlT, Bangkok
path; and
(5) various other economic reasons.
Metropolitan Admin istration Sport Center (BMA­
An urban heat island relates to local climatic
Stadium in Bangmod), and the green conserva­
change, it only affects large cities, unlike global
tion area at Bangkrachao (BKC) which belongs
warming which affects the global climate. Al­
to the Office of Environmental Policy and Plan­
though affected areas are very small, the percent­
nmg.
2. Satellite imagery data from NOAA,
age of affected population may rise to 50% in the
21 st cen tury.
An urban heat island may cause environmen­
tal problems in
w;.u
. m
regions such as;
Landsat TM thermal bands, maps and Geographic
Information System (GIS) data were used for ana­
(1) increase energy use for air-condition ing
lyzing the spatial structure of land use and land
cover.
(2) increase in peak electricity demand, with
3. A Thermo Graphy System which remotely
unstable electricity supply, or black outs
(3) change in biodiversity
(4) higher mortality on hot days
(5) acceleration of air and water pollution
(6) human discomfort, which may affect life
style and culture
measures the surface temperature distribution of
an object through infrared radiation, 'was set up
on the 20th floor of the new building in the Fac­
ulty of Engineering, Chulalongkorn U niversi ty to
measure the heat discharged from various land
covers in and around the University.
This project aims to establish a monitoring
system to understand the UHI formation mecha­
Results
n ism as the first step, and to finds policies for miti­
gation as the second step.
1. Diurnal variation and heat island inten­
sit),
Methodology
The heat island intensity was defined as the
temperature difference between the city center:
Three measurement systems were used in this
study: measuremen t of heat islands, measurement
Chulalongkorn University (CD) and a suburban
area: Asian Institute ofTechnology (AlT). Accord­
of land-use/land cover, and measurement of an­
ing to a series of land use / land cover maps of
Bangkok (LandsatTM, 1988, 94, 98) (2,3) which
thropogenic heat discharge.
I. A network of automated ground-base
monitoring stations':" was established for con­
tinuous observation. In Bangkok, 7 Davis stations
provide 30 minute interval weather data (tempera­
ture, relative humidity, solar radiation, precipita­
tion, pressure, wind speed and wind direction).
They are: Asian Institute of Technology (NT);
Chulalongkorn University (CU); Kasetsart Univer­
sity (KU); King Mongkut's Institute of Technol­
(;0
showed the relationship between the heat island
intensity with the built-up area of Bangkok. Heal
island intensity observed from North-South axis
located ground stations on 15 fine days during
February 13th-28th 1998 showed diurnal variation
of heat island intensity profiles (Fig.la). The on­
set of an urban heat island became evident after
sunset, and reached a maximum of 3.5°C during
6:00-7:00am. It was noted that heat island inten­
JournalofJlealth Science 2000 Pol 9 JVO. 1
Changing
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Diurnal variati on of Heat Island Intensity ( a) , Temperature profil es of s-stations in the North-South axis
showing he at island intensity weakened by sea breeze , solar radiation, roughness, dust density during
dayt ime (b), stren gth ened by human activity, energy consumption and thermal radiation from buildings
(c).
Urban Heat lsland : Thermal Pollution and Climate Change in Bangkok
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Fig. 2 (a) Vertical air temperature profiles observed by balloon experiment. CU and AIT on March 3t/99
between CU and Bangkrachau (BKC) on April 2
(b) Vertical air temperature profiles ob served by balloon experiment. CU and Bangkrachau (BKC) on
April znd
C:trJ
Journal ofJiealth Science 2000 Pol. 9
,No_1
Fig.
3
Area
Box
Average temperature "C
38.7
1
Box 2
Box 3
31.3
34.6
Landscape of Chulalongkorn University (a) and its thermal image (b) taken on March
12:06:09 LST. Box 1: roof of building; Box 2 : trees; and Box 3 : grass land.
sity decreased to -1.5 "C in the afternoon. This phe­
nomenon could be explained by the combination
effect of sea breeze (Fig. 1b) and solar radiation.
Starting from 13:00hr, the ground temperature
at SEAFDEC and KlvIUrr which were nearer to
the sea became cooler, and also at CU, compared
to AIT. In the day time, stronger solar radiation
'was observed at AIT and SEAFDEC compared to
CU and KlvI UTI, because of the roughness of the
built up area and dust density at CU and KMU1T
which reduced about 20% of solar radiation from
the 750 J.m o2 observed at AlT.
At sun set, temperature at AlT fell with loss
of solar radiation, whereas urban heat island
showed up the acumulative effects of human ac­
tivity, energy consumption, and thermal radiation
from buildings (Fig. Ie).
2. Effect of land cover type on vertical air
temperature profile
The comparison of vertical air temperature
profiles between AlT and CU confirmed the ef­
fect ofsea breeze at CU (Fig.2a) and KIvlUTI (Fig­
ure not shown) to be about one degree different
at a height of 20- 150 m duting 13.50 - 16.50 h.
Between AITand CU, stronger solar radiation ac­
30, 1999
at
counted for a difference of about 2°C, whichde­
creased by late afternoon. The most 'prominent
effect of green area (EKC) could be observed at
the canopy level of20 m, which was 2°C lower than
CU (Fig. 2b).
3. Remote measurement of potential heat
sources in urban areas
The thermal images detected by Thermo­
graphy system with respect to different types of
surface cover shown in Fig. 3a and 3b, marked by
Box L roof of building; Box 2: trees; and Box 3 :
grass land, showed that large trees had a much
higher cooling capacity com paved to grass land.
By this method the relative heat capacity of differ­
en t roofmaterials, color of m ateri als could be com­
pared in terms of apparent surface temperature
remotely and timely.
Discussion & Conclusion
The results indicate that the urban heat is­
land phenomena exists in Bangkok showing a di­
urnal variation with the highest intensity during
night time of about 3.5 °C in February 1998 be­
tween CU and AlT. Analysis, using Land-sat TM
data by Kurisaki et al. in January 1998 showed the
Urban Heat Island: Thermal Pollution and Climate Change in Bangkok
maximum heat island intensity of surface tempera­
lure up to 5.5°C which agree well with air tem­
perature profiles in this study. Comparing the
monthly average Heat Island Intensity (HII) in the
whole year 1998, seasonal variation was observed
with highest HII in january, decreasing to about
2.7 in September or "Rainy" season and minimal
during March and April. Komolveeraket, 19984 re­
ported the difference in surface temperature be­
tween downtown and suburban areas by Land-sat
TM data on April 24, 1997 at 1.7 °C, which was
similar to our results. All these results confirmed
the UHI phenomena of Bangkok.
Comparing the long term trend ofair by tem­
perature in Bangkok with Tokyo, the minimum
temperature of Bangkok has increased by 1.23 °C
in 50 years (from 23.39 °C in 1951), whereas To­
kyo experienced +2.8 °C rise in 135 years or about
1.03°C in 50 years!" The results indicate that large
trees can provide a cooling effect at 20-m level
down to ground-base temperature at 1.50 m level.
Sea breezes from a south direction can decrease
the air temperature in the southern part of
Bangkok. Difference in heat capacity of roof ma­
terials and color of buildings should be further
investigated in order to mitigate the heat dis­
charged from built up area. Good urban planning
is necessary to avoid blocking of sea breeze or
provide ventilation path into a mega-ciry.P'
(K1\UTL); King Mongkur's University of Techno1­
ogy, Thonburi (KivlUIT); Mahidol University,
Salaya Campus (MU); and Southeast Asian Fish­
eries Developmen t Cen ter (SEAFDEC) for ground
base monitoring stations, and permission for bal­
loon experiment at CU- Stadium, AIT, Bangkok
Metropolitan Administration Sport Center (BMA­
Stadium in Bangmod), and the green conserva­
tion area at Bangkrachao (BKC) which belongs
to the Office of Environmental Policy and Plan­
Acknowledgement
nal variations in the horizontal temperature distribution
using high density urban climate observation network in
Tokyo metropolitan area: a compararison of the summer
case and the autumn case , In : Interim report of Moni­
toring and Management System of Urban Heat Island
Project. Tokyo: japan Science and Technology Corpora­
tion; 1999.
5. Abt. Stadtk lim alol og ie. Amt fuel' Umwe ltachutz .
Landeshaupstadt stuttgart: Stadtklima 21- GruncUagen zu
K, lima Luft lind Laerrn foer die Planung "Stuttgart 21.~
1999.
This project is financially supported byJapan
Science and Technology Corporation, Southeast
Asia START Regional Center, Environmental Re­
search Institute, Chulalongkorn University. The
authors thank logistic support from Asian Insti­
tute of Technology (AJT); Chulalongkom Univer­
sity (CU); Kasetsart University (KU); King
Mongkut's Institute of Technology, Ladkrabang
OlOg.
References
1. Kubo S. Urban Heat Island Monitoring and Management
Project. Proceedings of International Symposium Moni­
toring and Managemen I of Urban Heat Island ; 1997 Nov
19-20; Fujisawa Campus, ,KEIO University. Tokyo :Japan
Science and Technology; 1997.
2. Kubo S, Niitsu K., Sai 1', Ohmori 1', Takahashi T. Installa­
tion of monitoring network and primary analysis of heat
island in Bangkok and Shanghai. In : Interim report of
Monitoring and Management System of Urban Heat Is­
land Project. Tokyo.japan Science and Technology Cor­
poration; 1999.
3. Komolveeraket K. The effec t of land U5e change on ur­
ban he at island phenomena in Bangkok [Master Thesis].
Bangkok: Chulalongkorn University; 1998.
4. Yanagiwa K, Ushiyama M, Mikarni T. A analysis of diur­
I Journal ofJif!rdlh Science 2000 VoL 9
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