KEYWORDS: air temperatures, urban climate map, building Density, vegetation

Transcription

1 URBAN CLIMATE MAPPING FOR SUPPORTING URBAN PLANNING IN CHENNAI, INDIA Ar.Ebin Horrison* & Ar.Lilly Rose** *Sathyabama University, Chennai, India, **Sathyabama University, Chennai, India, ABSTRACT: Urban climate plays an increasingly vital role in conceptualizing the growth of Metro cities as the thermal environment is severe particularly in hot and humid climate. The local authorities involved in planning and forecasting the future of such cities are however not sensitized to this phenomenon as the quantifying of the quality urban environment based on climate are minimal. The Urban Climate Map is model that helps in bridging this issue. The Urban Climate Analysis Map also helps in identifying areas in the city which are at risk of heat storage. This paper aims at developing a urban climate map for the hot humid city of Chennai in India. The urban climate map will be developed based on the climatic parameters derived from in-situ field measurements are then compared with population density map to understand the relationship. The Urban climate map thus developed will be a decision support tool for planners and designers in creating a climate sensitive Urban Environment. KEYWORDS: air temperatures, urban climate map, building Density, vegetation 1. INTRODUCTION Rapid urbanization has largely altered urban climate made obvious by high air temperatures in densely populated areas. The air temperature trend is a critical factor that determines comfort conditions. An analysis of historic climatic data of Chennai city from two meteorological stations in Chennai (Nugambakkam & Meenambakkam) indicates a significant increase in the air temperature trends from 1988 to 2008 (Rose 2010). The increase in the air temperatures determines the thermal comfort at the canyon level and is proportional to the urban built-up and population density. This paper aims at developing a urban climate map based on population density for the hot humid city of Chennai in India. 2. AREA OF STUDY Chennai-Madras, a metropolitan city of India, is located on the Coromandel Coast of the Bay of Bengal. Chennai located at N latitude and E longitude, has a flat coastal plain with an average elevation of 6m. Chennai experiences hot humid type of climate with the relative humidity reaching 80% in the month of November. The maximum air temperature (May) reaches 42 c and the minimum air temperature (December) drops to 18 c. The city skyline is predominantly low rise medium density which is an outcome of development control rules existing in Chennai. 3. METHODOLOGY Air temperature and relative humidity data were measured at 30 fixed locations in and around the CMA for the month of May at 14:00hrs. The temperature isopleth for CMA have been interpolated using ArcGIS. The air temperatures were analyzed and the results were compared with the population density map (CMDA 2008) to understand and establish the correlation between the two.

2 4. CHARACTERISTICS OF THE MEASUREMENT SITES IN THE CMA The measurement sites were chosen such that, it covers the different residential neighborhoods within the city limits and few suburban residential neighborhoods, institutional areas, and rural areas illustrated in the Fig. 1. Figure 1 The location of the residential neighborhoods in the CMA The stations chosen were homogenous and the characteristics of the fixed measurement sites are shown in Table 1. Table 1 Characteristics of the measurement sites in the CMA S. No Location Description 1 Triplicane Coastal traditional settlement in the east with high density and high traffic 2 George Town A mixed residential area in the old city with very high density and very high traffic with no vegetation 3 Old Washermanpet Old settlement with high density, medium traffic and no vegetation 4 Purasawakkam A perfect mixture of commercial and residential hub with very high density and very high traffic 5 Mount Road Central Business district with high density and very high traffic 6 Santhome A fishing settlement close to the sea in the east with medium density and medium traffic 7 T. Nagar A medium density residential area with few parks and very high traffic. 8 Kodambakkam Residential zone with medium density, medium dense vegetation, high traffic 9 Koyambedu A major hub of activity zone with one of Asia's largest perishable goods market complex and Asia's largest mofussil bus terminus accompanied by medium density and very high traffic. 10 Perambur Suburb in North Chennai with medium density and medium traffic

3 Table 1 (Continued) S. No Location Description 11 Thirumangalam Primarily a residential neighbourhood with medium dense vegetation, medium density and heavy traffic 12 Virugambakkam One of the fastest growing residential neighbourhoods with medium density and medium traffic 13 Saidapet Largely a residential area with medium density and medium traffic 14 Adayar A residential neighbourhood in the south with medium density, dense vegetation and high traffic 15 Besant Nagar Primarily residential neighbourhood adjoining the theosophical society and Kalakshetra academy with medium vegetation, medium density and medium traffic 16 Velachery A fast developing residential area in south west Chennai with medium density and medium traffic. 17 Madhavaram An industrial zone with low density and medium traffic 18 Chrompet A fast growing residential neighbourhood in the suburbs, with medium density, medium traffic and medium dense vegetation 19 Kolathur Newly developing residential area with low density and low traffic 20 Valsarawakkam Low density residential area with medium traffic and more open areas 21 Ambattur A residential neighbourhood with low density, low traffic, and medium dense vegetation 22 Redhills A low density suburban area with low traffic close to Puzhal lake 23 Thiruverkadu Low density, low traffic with more open spaces and medium vegetation 24 Kilkattalai A newly developing residential neighbourhood with low density and medium traffic 25 Anna University An institutional zone close to the Guindy National Park and Raj Bhavan with high dense vegetation, low density and medium traffic 26 Adayalampattu A suburban low density institutional zone with more open spaces 27 Sholinganallur A suburban institutional zone with low density, medium traffic and more open space with less vegetation 28 Sekkadu A rural agricultural area with low density and low traffic 29 Vandalur A rural area adjoining Anna Zoological park with dense vegetation, low density and medium traffic 30 Chengalpet A rural low density residential zone with less traffic 5. RESULTS AND DISCUSSIONS The maximum daytime temperatures were recorded between 11:00hrs and 15:00hrs at 30 fixed locations were characterized by their urban morphology, and the time of exposure of the measurement location to direct solar radiation. Therefore, the analysis of the temperature isopleths at 14:00hrs (period of intense solar radiation) reveals the nature of intra urban air temperature intensity in the CMA. Figure 2, shows the temperature isopleths of the CMA at 14:00hrs of the measurement periods. Figure 2, clearly shows that the temperatures during the summer month (May) in the urban areas were lesser than those of the rural areas, ranging up to 10.4 o C. At 14:00hrs, all the measurement locations in the CMA with a few exceptions (Mount Road, Virugambakkam, and Thirumangalam) were cooler than the rural areas. During daytime, minimum temperatures were recorded in narrow streets with high density urban built up (George Town, Old Washermanpet, Saidapet) and at locations characterized by dense vegetation (Anna University, Adayar, Besantnagar).

4 Figure 2 Temperature isopleths of May at 14:00hrs In the urban areas the shading effects of the buildings and vegetation reduced the daytime temperatures significantly. The sea breeze along the coastal areas in the afternoons also reduced the air temperatures significantly (Santhome, Triplicane).The maximum temperatures during daytime were recorded at locations with rural characteristics (Sekkadu, Chengalpet, and Vandalur). The sites characterized by wider streets where the shading effects of buildings and vegetation is either absent or negligible (Thirumangalam) and with low rise urban built up, recorded temperatures almost similar to those of the rural areas during daytime (Ambattur, Virugambakkam). Anthropogenic heat and the material properties (albedo) have also been found to affect the urban air temperatures significantly (Purasawakkam). Purasawakkam, characterized by narrow street geometry recorded maximum temperatures throughout the measurement periods; this can be attributed to the high degree of anthropogenic heat emission and use of bright colours on the facades.

5 Figure 3 Population density map of Chennai 2006 The comparison of the population density classification image (Fig. 3.) and the Temperature isopleths of May at 14:00hrs (Fig. 2.) through visual interpretation revealed the following: The dense urban built up areas and vegetated areas get heated up slowly when compared to the surrounding rural areas resulting in cool pockets within the urban core. The intensity of the cool pockets observed during daytime in the urban areas becomes prominent with daybreak and reaches its peak around 14:00hrs. The daytime temperature isopleths of the summer period also reveal that the urban areas shaded by dense urban built up were cooler than the rural areas by up to 10.4 o C at 14hrs. A few urban sites also recorded higher air temperatures when compared to the rural areas. This increase in the ambient air temperatures can be attributed to the heating up of the hard surfaces of the urban built up areas, characterized by low rise and wide road network with direct solar radiation.

6 6. CONCLUSIONS The outcome of the study clearly indicates a strong relationship between built density and air temperature variations. The findings on thermal comfort can therefore be a strong element in planning Chennai city future growth. The study also underlines the fact that thermal comfort conditions can be improved developing medium-rise medium density and high-rise low density zones. REFERENCES [1] Ali-Toudert F., Dependence of outdoor thermal comfort on street design in hot and dry climate, PhD Thesis, University of Freiburg, Germany, pp , [2] Rose.L., Effect of urbanization on urban heat island and thermal comfort in Chennai metropolitan area,india, PhD Thesis, Anna University,Chennai, pp , [3] Chennai Metropolitan Development Authority (CMDA), Second Master Plan for Chennai Metropolitan Area, 2026, Vol. I, pp.26-60, [4] Chennai Metropolitan Development Authority (CMDA), Second Master Plan for Chennai Metropolitan Area, 2026, Vol. II, pp.22-43, [5] Chennai Metropolitan Development Authority (CMDA), Second Master Plan for Chennai Metropolitan Area, 2026, Vol. III, pp.1-10, [6] Correa C., The New Landscape: Urbanization in the Third World, London: Butterworth Architecture, pp.34-40, [7] Ellefsen R., Mapping and measuring buildings in the urban canopy boundary layer in ten US cities, Energy and Buildings, Vol.15-16, pp , 1990/91. [8] Givoni. B, Climate Considerations in Building and Urban Design, New York, Van Nostrand Reinhold, pp , 1998.