We have all experienced it – the temperature elevation that welcomes us as we enter an urban zone from greener, rural regions. Known globally as the Urban Heat Island effect, it is universally accepted as a side-effect of urbanization and the mainstay of any metropolis. Observed since the 19th century, the Glossary of Meteorology (2009), defines the term as any region within a large city which is significantly warmer in the night than its surroundings, though theoretically, the island may be created at any time of the day in the year. The numerous contributors to rapid and heavy urbanization, such as modification of land surfaces, reduction in vegetation in urban areas and overall concretization of urban surfaces are among the primary reasons for the formation of an urban heat island.
As a city blessed with deep natural harbours and vast stretches of natural wetlands, Mumbai in its original ecosystem of wetlands, marshes, creeks and mangrove forests has supported some of the densest biodiversity within the subcontinent until the turn of the century. This landscape has afforded the city uniform and moderate climate throughout the year. However, upon closer study, the microclimatic regions of the city reveal a disturbing picture. Depending on the nature of built strata, heat islands of varying degrees are created regularly over specific zones of our megapolis.
Previous research on heat islands in Mumbai identified traditional industrial hubs in the east and the densely built-up island city as generators of heat islands. A fundamental takeaway from the study highlights the difference in temperatures in the island and mainland areas of the city due to the lack of adequate wetlands and national parks in the south. It is also worrisome to realize that the expanse of coastline in the island city is insufficient to counter the effects of heat island formation in south and central areas. The difference in temperatures in multiple heat islands across a single urban sprawl is further cause for upset in the original climate of the city.
Heat islands have relentlessly followed urbanization with every leap in land use, engulfing humankind with adverse effects on climate, vegetation and ecosystems. Smaller cities such as Bhubaneswar have also observed similar patterns in heat island generation as Mumbai owing to exponential urban growth in the last fourteen years. Beyond the obvious changes in landscape such as reduced dense vegetation, shrinkage in natural water bodies and smog, there is the insidious consequences of shift in precipitation patterns and their direct impact on crop cycles. The disconnect between the natural climate of a specific geography and urbanization is increasingly difficult to bridge with our consumerist lifestyles – replete with unsustainable use of materials and indifference to emission control.
The impact of our self-created urban heat islands on the city can still be reversed. As we gradually realize just how massive our carbon footprint is, it is perhaps time to visualize the thermal imagery of our city. The visuals are certain to help us question the sustainability of our existence. Are we really using building materials intelligently enough to blend harmoniously with our habitat? Are the very substances we use to build our shelters interfering with our ecosystem to bring upon our doom? If the regular episodes of heat waves we are experiencing over the last few years are any indication, we are living in very uncomfortable times – and climes.