The Impacts of Sea Breeze on Urban Thermal Environment in Tropical Coastal Area

Transcription

1 Advances in Natural and Applied Sciences, 6(1): 71-78, 2012 ISSN This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLE The Impacts of Sea Breeze on Urban Thermal Environment in Tropical Coastal Area Shaharuddin Ahmad, Noorazuan Md. Hashim, Yaakob Mohd Jani and Noraziah Ali School of Social, Development and Environmental Studies, Faculty of Social Sciences and Humanities, National Universty of Malaysia Bangi, Selangor, Malaysia Shaharuddin Ahmad, Noorazuan Md. Hashim, Yaakob Mohd Jani and Noraziah Ali; The Impacts of Sea Breeze on Urban Thermal Environment in Tropical Coastal Area ABSTRACT A study on the impacts of sea breeze on temperature distribution was carried out in Kuantan, Pahang, which is a tropical coastal regional urban growth center in Malaysia, for three days i.e. 11 to 13 February 2011 during the end of the north-east monsoon. Two temperature and wind speed traverses of about 10 km long were formed perpendicular to the shoreline of Kuantan. Temperature, relative humidity and wind speed data were measured at about 1.5 m above the ground at several points along these traverses. Hourly measurements were taken contineously for about 15 hours starting from 08:00 until 22:00 Malaysian Locat Time (MLT). The result showed that B3 was the station with the earliest onset time of sea breeze i.e. around 12:00 MLT as well as the longest formation of sea breeze i.e. about six hours. The negative sea breeze-air temperature correlations, r, of between 0.01 and 0.33 were calculated for both traverses. The range of temperature reduction due to wind speed of the sea breeze magnitude was between 0.2 C to 5.3 C. Positive correlation was observed between air temperature and relative humidity for all stations with the smallest and highest increment of relative humidity of 2.2 and 16 percent were calculated at stations A3 and B3, respectively. In conclusion, the furthest impact of sea breeze on urban thermal environment towards inland of Kuantan was about km from the coastline of Teluk Cempedak. These findings are deemed important input for the future urban planning of Kuantan, especially the urban infrastructure to provide a comfortable and a conducive thermal environment for the urban dwellers. Key words: ; cooling effect; comfort; wind speed; thermal environment Introduction has long been known as one of the local wind circulations, particularly along coastal areas, lakes, rivers or at and around islands. It is a thermal induced wind because of the differential heating between land and sea during the day (Shaharuddin 1998; Bastin et al. 2005). The heat contrast between land and sea creates an onshore pressure gradient force at low level in the atmosphere and a shallow layer of marine air moves inland and hance a daily phenomenon for most of coastline cities in the world. In the mid-latitude regions, for example, sea breeze becomes a natural cooling source in improving the urban thermal environment. Several studies conducted in determining the cooling effects of sea breeze on urban climates, particularly for coastline cities (Estoque, 1961; Frizzola et al. 1963; Katayama et al., 1991; Shaharuddin 1993, 1998; Federico 2010) and interior areas (Estoque, 1961; Simpson, 1994). However, the impact of sea breeze on urban thermal environment is very much depending on its intensity. Generally, its intensity depends on several factors such as thermal forcing, large scale winds, atmospheric stability, cloud cover, land uses etc (Federico et al. 2010). In tropical regions, sea breeze intensity can reach 7.7 ms -1 (Nieuwolt 1977). It is estimated that cooling effect of sea breeze can reduce daily ambient air temperature within coastline cities as high as 4 C (Shaharuddin 1998). However, it is believed that the presence of several tall buildings and hilly ground along coastline can prevent sea breeze from reaching the inner areas and warmer parts of coastline cities. Based on previous studies, sea breeze had an important effect on out-door comfort conditions (Banfield, 1991), building architecture and urban planning, especially coastline towns (Landsberg, 1970: Givoni, 1974) and density of population along coastal areas in the mid-latitude region (Pielke, 1975). Other studies had shown that sea breeze also an important agent of matter and energy transport, dispersing of urban air pollutants (Lyons Corrrseponding Author: Shaharuddin Ahmad, School of Social, Development and Environmental Studies Faculty of Social Sciences and Humanities Universiti Kebangsaan Malaysia Bangi, Selangor, Malaysia shah@ukm.my

2 72 and Olsson, 1973; Cole, 1977; Nieuwolt, 1977; Kolev et al. 2000), ozone distribution (Liu et al. 2002; Oh et al. 2006) and urban thermal environment (Tsutsumi et al. 1991; Shaharuddin 1998). Although sea breeze is considered as one of the important climatic phenomena studied in the mid-latitude regions, it rarely becomes an important subject to be observed and studied in the lower latitudes, including Malaysia. Perhaps, this is due to the fact that most of the people thought that weather in tropical area, such as in Malaysia is not harmful and create uncomfortable environment to daily life. Meteorologically, the tropical region is a source of heat generation and thus more low and high air pressures established on the land as well above the sea area. Because of this situation, therefore, wind systems develop between different pressures, especially between land and sea areas. In reality, however, tropical weather is also producing and creating good and bad phenomena as observed by-products of other world weather. As insular country of the main Asia continent, coastline towns in Malaysia are definitely not exceptional from experiencing land and sea breeze phenomenon. Nevertheless, the extent the town experiences such phenomenon will depend on the seasonal variation and prevailing winds that determine the thermal properties of land and sea. On this note, therefore, this study attempts to investigate the onset time and duration of sea breeze formation as well as its significant impacts on urban thermal environment in Kuantan, Pahang, Malaysia. Materials And Methods Description of the study area: Kuantan town is the capital of the state of Pahang, Malaysia ( 3 50 N and E). It is located on the right side of the Kuantan river estuary (Figure 1). Kuantan has been considered as one of the towns in the east coast of Malaysia that has gone through a rapid urban development since the end of the last 20 th century. Kuantan town bordered with The South China Sea on the east side and Terengganu state on the northern side. Kuantan river is located at the southern side of Kuantan. Generally, Kuantan is a flat land which is about 2-5 meter above the sea level. However, there is one hilly are at the north eastern side of Kuantan so-called Bukit Pelindung. Based on the present data, the total population of Kuantan is about 607,778 people, representing the ethnic of Malay, Chinese, Indian. N Traverse A Traverse B A1 Observation point To Sg. Lembing/ Panching J. Dato Lim Hoe Lek A3 Jln Hj. Ahmad Jln Air Putih Jln Galing Jln Beserah Jln Alur Akar To Terengganu/Cherating/ Kuantan Port Jln Tok Sira km Jln Bukit Ubi Jln Dato Wong Ah Jang Jln Bukit Sekilau B3 Jln Penjara J. Tanah Puteh J Tun Ismail Jln Gambut Jln Besar KUANTAN RIVER A2 B2 Tanjung Lumpur Jln Selamat Jln Tanjong Api Jln Teluk Sisek B1 Jln Dato Abdullah Jln Teluk Chempedak Royal Pahang Golf Club SOUTH CHINA SEA To Teluk Chempedak THAILAND PENINSUL AR MALAYSIA A1 SOUTH CHINA SEA Kuantan, Pahang To Kuala Lumpur/ Kuantan Air Port To Pekan STRAIT S O F MAL ACCA Fig. 1: Location of point sources of temperature measurements in Kuantan, Pahang. Table 1 shows the mean monthly temperature, relative humidity and rainfall in Kuantan for nine-year period ( ). Based on this data, Kuantan experiences a hot and wet tropical climate throughout the year. The annual mean temperature is about 26.8 C with monthly mean temperature varies between 25.5 C in January and 27.9 C in May, giving the monthly mean temperature range of about 2.4 C. Maximum and minimum mean temperatures are observed around April-August and December-January, respectively. In

3 73 addition, the mean maximum and minimum temperatures were calculated at about 32.0 C and 23.5 C, respectively. Therefore, it gaves the maximum-minimum temperature range of about 8.5 C. The monthly total of rainfall for the nine-year period was calculated at about mm. In terms of monthly values, the maximum rainfall was observed a few months towards the end of the year, while the minimum rainfall established around April-June period. Meanwhile, relative humidity varies between 85.2 percent in December and 78.2 percent in July, producing the monthly range of about 7.0 percent. It is obviously observed that the relative humidity distribution is in association with the distribution of monthly temperature. Based on this climate pattern, it is obvious that Kuantan experiences a wet atmospheric condition throughout the year. Table 1: Temperature, rainfall and relative humidity at Kuantan, Pahang for the 9-year period ( ). Months Max Temp. ( C) Min. Temp. ( C) Mean ( C) Rainfall (mm) Relative humidity(%) January February March April May June July August September October November December Mean/Total Method of data collection: Two traverses were formed perpendicular to the coastline towards Kuantan town. Each traverse is about 10 km long, consisting of three point sources. One traverse runs from Teluk Cempedak towards Kuantan and end up at around Bukit Ubi area. The first station was located at Teluk Cempedak ( N and E) followed by the second station near business area ( N and E) and the third station at the junction of Jalan Dato Lim Hoe Lek and Jalan Bukit Sekilau ( N and E). Meanwhile, the second traverse runs from Taman Gelora (at the Kuantan estuary, N and E) through Kuantan town ( N and E) along the Kuantan river and end up near Hospital area ( N and E). Field survey was carried out for three days i.e February 2011 during the end of the north-east monsson period. Data on temperature, relative humidity, wind speed and direction were measured at about 1.5 m above the ground at each station with one hour interval starting from about 08:00 Malaysian Local Time (MLT) in the morning and stop at about 22:00 MLT at night. Temperature, relative humidity and wind speed at selected point sources were obtained by using mini hygro thermo-anemometer Extech s Model The instrument has the temperature, relative humidity and wind speed accuracy of 1 C, 5% and 0.2 m/s, respectively. Meanwhile the resolution for the temperature, relative humidity and wind speed is 0.1 C, 1% and 0.1 m/s, respectively. Fieldwork was assisted by ten field assistants. At least three to four readings were taken for each weather parameter at each point source and then the readings were averaged to represent weather parameter at that particular time and point source. The final data was then transformed into diagrams to observe the onset time and cessation of sea breeze at both traverses. Based on Nieuwolt (1977) definition wind speed of the magnitude of 4.1ms -1 was considered as sea breeze in this study. Besides, simple Pearson correlation technique was employed to establish the relationship between air temperatures and wind speeds at all observed stations. Results And Discussion Figure 2 a and b show the diurnal pattern and penetration of sea breeze of the speed 4.1 ms -1 at two traverses during the three days of observation i.e February 2011 in Kuantan, Pahang. Generally, the onset time and cessation of sea breeze were detacted at different time of the day at stations A1 and A2. However, sea breeze was untraceable at station A3 i.e. the furtherst observation station from the shoreline of Teluk Cempedak. The earliest onset time of sea breeze was observed at around 13:00 MLT and 14:00 MLT at station A1 and station A2, respectively. The formation of sea breeze at station A1 was lasted for about five hours i.e. until about 18:00 MLT in the evening. However, at station A2, sea breeze episode was lasted for about 2½ hours only i.e. up to 16:30 MLT in the early evening.

4 Wind vector 1200 Sea Breeze Sea Breeze Sea Breeze Sea Breeze m/s Adv. in Nat. Appl. Sci., 6(1): 71-78, The strongest and longer period of sea breeze of about six hours (12:00 until 18:00 MLT) was observed at station B3 of traverse B (Figure 1 and Figure 2b). This station is located not far from the Kuantan River and therefore more expose to wind from open river as well. Meanwhile, the onset time of sea breeze was much later at station B1 and B2 i.e. around 15:00 MLT. At both stations, the duration of sea breeze episode was lasted for about three to four hours only. It was clearly shown that at both traverses, the onset time of sea breeze was not observed before mid-day. In addition, the mean duration of the sea breeze episode was varied according to observed stations. In general, the longest mean duration of sea breeze was observed at traverse B rather than at traverse A i.e. 4.5 hrs against 3.5 hrs. This is due to the fact that traverse B was approximately located near and along the Kuantan River. Therefore, besides receiving the influence of sea breeze, stations at traverse B were also influenced by river breeze significantly. (a) (b) A1 N B1 N A2 A3 Wind speed B2 B3 5 m/s Temperature( C) Station A1 Station A2 Station A3 Temperature ( C) Station B1 Station B2 Station B Malaysian Local Time (MLT) Malaysian Local Time (MLT) Fig. 2: Diurnal variation of temperature and wind speed at two traverses in Kuantan, Pahang on February 2011; (a) at stations A1 A3; (b) at stations B1 B3. Further analysis was carried out to determine the significant association between sea breeze episode and the advancement of hourly air temperature in Kuantan, Pahang. Generally, it was observed that the advancement of sea breeze had a significant impact on the slowing down the increament of late morning air temperature as measured at both traverses. Furthermore, the decrease of late afternoon temperatures were closely associated with the formation of sea breeze episode after mid-day. This is particularly observed at stations A1, B1 and B2. However, the impact of sea breeze on the slowing down of the advancement of the morning air temperatures and decreasing the late afternoon air temperatures were not detacted at other stations, especially at station A3. In order to establish relationship between air temperatures and wind speed, simple Peason correlation was employed and presented in Table 2. Even though the results showed a weak negative correlation for all stations, its implied that the increment of wind speed of the sea breeze magnitude had an impact on the reduction of an advancement of air temperature. Therefore, it can be said that sea breeze, to some extent, plays an important role in reducing an advance air temperature within the coastline urban area such as in Kuantan, Pahang. Thus, the presence of sea breeze episode regularly within coastal urban area can be used as one of the methods of mitigating of excessive urban thermal as manifested by higher urban air temperatures or urban heat island. Table 2: Relationship between sea breeze and air temperature changes at two traverses. Traverse/Stations Traverse A A1 A2 A3 Traverse B B1 B2 B3 Sea Breeze and Urban Thermal Environment Pearson correlation, r The cooling effect of sea breeze on the thermal environment especially after mid-day was calculated (Table 3 and Figure 3 a and b). Normally, the cooling effect of sea breeze can be seen and observed one or two hours after the onset time of sea breeze episode at all stations. The overall impact of temperature reduction was

5 75 calculated at about 2.8 C and 2.5 C for traverse A and traverse B, respectively. The range of temperature reduction was calculated between C and between C for traverses A and B, respectively. It implies that individual station displayed different impact of sea breeze on the temperature reduction. For traverse A, it was calculated that station A3 had the most impact of temperature reduction by the presence of wind speed of the sea breeze magnitude i.e. 5.3 C. Meanwhile at traverse B, the biggest temperature reduction was calculated at station B1 i.e. 4.3 C. Table 3: The impact of sea breeze on temperature reduction at all observed stations. Traverses/stations Traverse A A1 A2 A3 Mean Traverse B B1 B2 B3 Mean Temperature reduction ( C) This finding is obviously different than what Shaharuddin (1998) found for Kuala Terengganu whereby the temperature reduction was not traceable for the inland station. One of the possible explanation to this finding is that, in general, station A3 is located at semi-urbanized area. At this station most of the morning incoming solar radiation produced excessive heat to surrounding environment, thus increase the air temperature significantly. However, due to the mix structure of the area i.e. partly covered with more green than built-up area, the excessive heat was not store as latent heat. Instead, after mid-day most of the heat release back to space without giving impact to warm the environment. Moreover, more heat use-up by vegetations for evapotranspiration as well as photosynthesis processes. In addition, with the presence of wind speed of the sea breeze magnitude it boosts further in temperature reduction at that particular station. Relative humidity is also affected by the presence of wind speed of the sea breeze magnitude. Further analysis was carried out to find the relationship between the air temperature and relative humidity (Figure 3 a and b). The decrease in air temperature was followed by the slight increase in relative humidity one or two hours later. This situation was observed especially for stations at the coastal areas i.e. stations A and B. For example, an increase of about 7.7 percent of relative humidity was calculated for A1 between 13:00 and 16:00 MLT whereas at A3 the value was only about 2.2 percent (between 13:00 and 16:00 MLT). For traverse B, the increment of relative hmidity with the decrease of air temperature was slightly more as compared with situation as observed at traverse A. For instance, an increase of about 16 and 15 percent of relative humidity was observed at stations B2 and B1, respectively. It took about 4 to 6 hours for relative humidity to increase after the onset time of sea breeze at both stations. Perpendicularly, the impact of sea breeze on the urban thermal environment of Kuantan could be restricted to about km from the coastline of Teluk Cempedak towards inland of Kuantan. However, if the combination of the Kuantan river breeze and sea breeze was taken into consideration, then the impacts of wind speed of the sea breeze magnitude could be traced more in inland areas of Kuantan. Planing Implications: Although sea breeze in Kuantan is not capable of reducing ambient air temperature as much as experiences by other cities in the mid-latitude regions, it is important for the urban communities to know the presence of sea breeze. This is a relevant aspect for them to plan their out-door recreational activities as not to coincide with the time of optimum uncomfortable out-door conditions. This is not only for daily out-door recreational activities, but also the monthly activities. It is clearly seen that in certain months of the year, especially during the northeast monsoon, the effect of sea breeze on air temperature is well observed. However, during this period of the year, the other factor should be considered as well that is the heavy rains which hinder a lot of out-door activities. It must be remembered that the penetration of sea breeze into the central business district is very much limited due to the obstacle of parallel hill of Bukit Pelindung along the coastline and tall buildings. With reference to urban development in Kuantan, as more and more tall buildings are being built near or along the coastal area but only to form obstacle to flow of sea breeze towards inland. Hence, in order to allow the significant effect of sea breeze into the inner area of Kuantan, the present policies should focus on new orientation of urban planning and to allow and to ascertain the presence of open spaces at the coastal area. In relation to this, areas congested with buildings are not only reduced the horizontal flow of air but also will increase the concentration of air pollutants. The warm and humid conditions, especially inside buildings will encourage the use of mechanical cooling devices, especially air-condition. The high rate of air-conditioning usage, on the other hand, will becomes one of air pollutant sources in the urban environment, including the

6 Relative humidity (%) Wind speed (m/s) 1000 Initial sea breeze at station B3 Initial sea breeze at station B2 Initial sea breeze at station B Adv. in Nat. Appl. Sci., 6(1): 71-78, problem of CFC. Therefore, the arrangement and location of buildings in town, especially within the congested area must be arranged in such a way that is permitted for sea breeze to penetrate further inside and through buildings. Besides, buildings should have more ventilation in order to create air circulation freely. (a) Relative humidity (%) Temperature ( C) Wind speed (m/s) Station A1 Station A2 Station A3 Formation of sea breeze at A1 Formation of sea breeze at A Malaysian Local Time (MLT) (b) Cessation of sea breeze at station B2 Cessation of sea breeze at station B3 Cessation of sea breeze at station B1 Temperature ( C) Station B1 Station B2 Station B Malaysian Local Time (MLT) Fig. 3: Diurnal variation of sea breeze formation at two traverses in Kuantan, Pahang on February 2011; (a) at stations A1 A3; (b) at stations B1 B3. Another factor that should be considered in planning the urban area is buffer zone. It is important to have more open spaces and green areas within the town municipality. It is more important to have such area between or near buildings. It is not only beautifying the area, but also, to some extent, reducing excessive urban thermal environment. Local features such as urban morphology and topography, to some extent, contributed in reducing and modifying the effects of sea breeze on urban thermal environment. Besides, building fountain in urban builtup area is recommended to reduce ambient air temperature (Shaharuddin et al. 2011).

7 77 Conclusions: The objective of this study was to investigate the presence of sea breeze and its impacts on the urban thermal environment of Kuantan, Pahang during the end of the north-east monsoon. The results of this study can be summarised as follows: (a) The onset time and cessation of sea breeze of the magnitude of 4.1 ms -1 was varied according to observed stations. The earliest onset time of sea breeze was observed at station B3 at around 12:00 mid-day and the latest at stations B1 and B2 at around 15:00 MLT. (b) The longest formation of sea breeze was observed at station B3 i.e. about six hours, beginning at around 12:00 until 19:00 MLT. The shortest formation of sea breeze was detacted at station B2 i.e. only about 2½ hours. (c) In general, duration of sea breeze formation at traverse B was about 4.5 hrs as compared to duration of sea breeze formation at traverse A was only about 3.5 hrs. (d) The advancement of sea breeze had an impact on the slowing down the increament of late morning air temperature for both traverses. In addition, the decrease of late afternoon temperatures were closely associated with the formation of sea breeze episode after mid-day, particularly at stations A1, B1 and B2. (e) The Pearson correlation revealed that the relationship between wind speeds and air temperatures had produced weak negative correlations for all stations. (f) The impact of sea breeze on the temperature reduction varied in magnitude as low as 0.2 C at station A2 to as high as 5.3 C at station A3. (g) The result showed that the negative correlation established between air temperature and relative humidity at all station. The values of relative humidity increment varied as low as 2.2 percent at station A3 to as high as 16 percent at station B2. References Banfield, C.E., The frequency and surface characteristics of sea breeze at St. John's Newfoundland. Climatological Bulletin- Canadian Meteorological and Oceanografic Society, 25: Bastin, S., P. Drobinski, A. Dabas, P. Delville, O. Reitebuch and C. Werner, Impact of the Rhône and Durance valley on sea-breeze circulation in the Marseille area. Atmospheric research, 74: Boyouk, N., J.F. Léon, H. Delbarre, P. Augustin and M. Fourmentin, Impact of sea breeze on vertical structure of aerosol optical properties in Dunkerque, France. Atmospheric Research, 101: Cole, R.J., Climate and building design. Weather 32: Estoque, M.A., A theorotical investigation of the sea breeze. Quarterly Journal of Meteorological Society, 87: Federico, S., L. Pasqualoni, L.D. Leo and C. Bellecci, A study of the breeze circulation during summer and fall 2008 in Calabria, Italy. Atmospheric research, 97: Frizzola, J.A. and E.L. Fisher, A series of sea breeze observations in the New York city area. Journal of Applied Meteorology, 2: Givoni, B., Man, Climate and Architecture, Amsterdam: Elsevier Publication Co. Katayama, T., T. Hayashi, Y. Shiotsuki, H. Kitayama, A. Ishii, M. Nishida and J.I. Tsutsumi, Cooling effects of a river and sea breeze on the thermal environment in a built-up area. Energy and Buildings 15-16: Kolev, I., Skakalova and I. Grigorov, Lidar measurement of aerosol extinction profile in Black Sea coastal zone. Atmospheric Environment, 34: Landsberg, H.E., Micrometeorology temperature differentiation through urbanization. Urban Climates, WMO Technical Note, 108: Liu, K.Y., Z. Wang and L.F. Hsiao, A modeling of the sea breeze and its impacts on ozone distribution in northern Taiwan. Environmental Modelling & Software, 17: Lyons, W.A. and L.E. Olsson, Detailed mesometeorological studies of air pollution dispersion in the Chicago Lake Breeze. Monthly Weather Review, 101: Melas, D., I. Ziomas, O. Klemm and C.S. Zerefos, Anatomy of the sea-breeze circulation in Athens area under weak large-scale ambient winds. Atmospheric Environment, 32(12): Nieuwolt, S., Tropical Climatology: An Introduction to the Climates of the Low Latitude. New York: John Wiley & Sons Ltd. Oh, I.B., Y.K. Kim, H.W. Lee and C.H. Kim, An observational and numerical study of the effects of the late sea breeze on ozone distributions in the Busan metropolitan area, Korea. Atmospheric Environment, 40: Papanastasiou, D.K., D. Melas and I. Lissaridis, Study of wind field under sea breeze conditions; an application of WRF model. Atmospheric Research, 98:

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