Urbanization and its impact on urban heat Island intensity in Chennai Metropolitan Area, India

Abstract

Background: Urbanization results in the formation of heat pockets termed as "Urban Heat Island" (UHI) and their intensities depend on urban built geometry. This study attempts to assess the impact of urbanization on urban heat island intensity in Chennai Metropolitan Area (CMA). Methods/Analysis: Air temperature and relative humidity were measured at one hour interval at 30 fixed locations covering urban, suburban and rural locations in and around CMA. HOBO data logger (HOBO U10 Temp/RH), enclosed within a white perforated plastic box to shield the instrument from direct solar radiation were deployed for the study. UHI intensity was computed based on the reference data from Numgambakkam Meteorological station. Day time and night time temperature isopleths of CMA were derived using ArcGIS, including the isopleths at maximum and minimum temperature occurrences at 14.00 hrs and 06.00 hrs respectively. The temperature isopleths at 10:00 hrs, 14:00 hrs and 18:00 hrs were analyzed for daytime intensity of UHI and their temperature distribution pattern. Findings: Maximum daytime temperatures were recorded between 11:00 hrs and 15:00 hrs which varied between locations based on urban morphology and the time at which the measurement location is exposed to incident solar radiation. The daytime temperature isopleths at 14.00 hrs revealed the existence of a cool island in the urban core of CMA with a temperature difference of 10.4°C in summer and 3.7°C in winter. The night time UHI in the CMA was analysed with the temperature isopleths of 22:00 hrs, 02:00hrs and 06:00hrs. The night time temperature isopleths reveal the significant existence of positive UHI in the CMA. The isotherms at 06.00 hrs revealed a significant positive UHI ranging from 3.6°C in summer to 4.1°C in winter. The results of the study indicate a maximum nocturnal UHI during the calm, clear, winter periods in the CMA. The urban rural differences also revealed a significant cool island during the day with the maximum cool island intensity during summer. Applications/Improvements: A significant correlation between urban-rural differences and density of urban built form was established; indicating the significance of building regulations that define urban built geometry, in designing comfortable urban environments.