Urban heat island intensity and evaluation of outdoor thermal comfort in Chennai, India

The variation in the atmospheric conditions of urban areas to the fringe areas is termed as urban heat island and is attributed predominantly to the differences in the pattern of built environment. The aim of this study is twofold; firstly, to assess the heat island intensity in the tropical city of Chennai through traverse method and secondly to establish the relationship between the built environment and its contribution in altering the microclimate parameters. Air temperature and relative humidity were measured across the city through traverse survey. The data were analyzed by generating temperature and relative humidity isopleths, and hotspots in the city were identified. Eight fixed stations were located in Thyagaraya Nagar-one of the identified hotspots to study the spatial distribution of climate parameters using ENVI-met simulations. The study confirms the presence of UHI in Chennai with an intensity of 4.5 degrees C in winter and 2.5 degrees C in summer. At the micro-scale level, the study establishes a difference of 6 degrees C during daytime. The study revealed a maximum physiological equivalent temperature (PET) difference of 22 degrees C between the locations. The findings of the study would enable urban planners to develop comfortable newer neighborhood with thermally comfortable outdoor environments which will help in increasing pedestrian comfort.