Creation of cities leads to the removal of natural landscape with built up spaces, parking lots, roads etc, through highly reflective materials, affecting the local climate in a dramatic scale. The climatic changes in the urban areas are often characterized by increase in air temperatures and are termed as the Urban Heat Island Effect (UHIE). Major factors contributing to the elevated air temperatures include the size of the city, population, density of built-up spaces, street canyon geometry, thermal properties of materials, degree of vegetation and waste heat from buildings. Therefore it is vital for urban designers and urban planners to study the nature of the climate variation trends in urban areas to equip them in planning sustainable and comfortable cities, and mitigate the adverse effects. This paper aims to assess the intensity of urban heat island effect in the city of Chennai and their relationship to various urban factors, through stationary and mobile recordings of urban air temperatures during the hottest month. Air temperatures were recorded in 30 stationary locations covering urban, suburban and rural stations. A mobile survey was also conducted covering the major areas of the city. The results indicate the existence of heat island effect in the city of Chennai with increasing air temperatures in a radial fashion from the suburbs towards the city centre where the mean max UHI intensity reaches 5.5°C in stationary survey and 2.53°C in the mobile survey. The study reinforces the relationship between the urban air temperature increase and the land-use characteristics. Areas with dense vegetation recorded lesser air temperatures and high density built up spaces along with heavy traffic areas recorded higher temperatures. Further studies between these urban factors and urban air temperatures can lead to arrive at appropriate strategies to mitigate the heat island effect.

Key words: Urban Heat Island, Built-up density, Urban air temperatures, Urbanization, Land use, mobile survey.