Sustainable Planning Interventions in Tropical Climate for Urban Heat Island Mitigation – Case Study of Kolkata

Abstract

Urbanization plays an important role in the development of urban heat islands (UHI) in urban areas. UHI is a phenomenon where the urban built landscape shows a higher air temperature conditions than the surrounding hinterland and rural landscapes. Heat island also shows a lesser fall in temperatures than the adjacent outskirts and rural areas. The atmospheric concentration of GHGs has led to global climate change and because of the frequency of heat waves led to heat stress-related mortality and morbidity in mega high-density and compact cities located in the tropical and subtropical region of Southeast Asia. It is also observed that the city is divided into various microclimatic zones, and these zones are always in the process of continuous change due to unplanned and haphazard growth in urban built form.

In this study, the openness of the urban built form which can be measured by the sky view factor ratio and calculated by various techniques to find the distribution pattern in these various microclimatic zones is calculated and analyzed. SVF is the ratio of the radiation received (or emitted) by a planar surface to the radiation emitted (or received) by the entire hemispheric environment called the sky view factor or SVF (Watson ID, Johnson GT: Int J Climatol 7:193–197, 1987). The scale of SVF is ranged between 0 and 1, where SVF is 0 which means sky is fully obstructed and SVF is 1 which means there are no obstructions. Urban environments appear as uneven artificial terrains with building materials partly different from those of natural surfaces. Generally, its strongest development occurs at night when the heat, stored in the daytime, is released (Landsberg HE: The urban climate. Elsevier, New York/London, 1981; Oke TR: Boundary layer climates. Methuen Publishers, Lagos, 1987; Wienert U, Kuttler W: Meteorol Z 14(5):677–686, 2005). In Kolkata, narrow streets and high buildings create deep canyons. This 3D geometrical configuration plays an important role in regulating long-wave radiation heat loss. Due to the fact that only a smaller part of the sky is seen from the surface (because of the horizontal and vertical unevenness of the surface elements), the outgoing long-wave radiation loss here is more restricted than in rural areas.

This study outlines the urban built form typology in various microclimatic zones in Kolkata and its impact on land surface temperature and urban heat island variations. The chapter analyzes the relationship between the aspects of urban built form and sustainable planning interventions which are proposed to ameliorate the impact of urban heat island in Kolkata for improving the quality and usability of outdoor spaces in terms of human health and sustainable future.