SPOTS OF TROUBLE FOR URBAN REGIONS Thursday, 03 April 2014 With a variety of eco-friendly options available, it is surprising that the problem of urban heat spots continues to adversely impact the environment as well as the quality of life. Authorities ought to use the expertise available As merciless summers bear down on India, the urban communities face the additional prospect of abnormal and pronounced heat wave conditions due to consequences of rapid urbanisation. Vehicular pollution, energy-intensive buildings and power stations on the one hand, and excessive use of asphalt, concrete, and other impervious surfaces on the other, are resulting in increased solar absorption and heat emission. This phenomenon, termed as ‘urban heat spots’ or islands is made worse by the absence of convection as tall buildings block natural wind movement, thereby effectively trapping heat and causing the urban spaces to be hotter than their outskirts by nearly three-to-four degrees. Growing pollution in a concretised environment is taking a toll on the overall health of the urban communities as respiratory problems and associated disorders are witnessing a spike, especially in the summer months. The heat spots or islands are making the situations worse. Delhi is an apt example with surface temperatures having risen by two-to-three-degree centigrade in the past three decades, thanks to rising population, massive urbanisation and diminishing green cover. But how have the conditions come to such a state, is the question that the authorities concerned need to contemplate upon. Cities that are established in arid areas show far less heating than urban areas built amid forested and temperate climates. And therein lies the solution. The amount of the heat variance between the city and the surrounding environment depends on how much of the ground is covered by trees and vegetation. It is natural that as cities develop, more vegetation is lost as surfaces are paved or covered with buildings. Therefore, a planned urbanisation that includes measures for mitigation of urban heat spots is an absolute need of the hour. This will help build new and better cities, besides retrofitting the existing ones. The renewed urban planning, apart from enabling increased vegetation cover in the city, should push for controlling rampant constructions and ensure stringent air quality controls. An enhanced green cover will help cool the urban environment through shading and evapotranspiration. The process of evapotranspiration enables trees and vegetation to absorb water through their roots and emit it through their leaves. This movement of water is called ‘transpiration’. Evapotranspiration cools the air by using heat from the air to evaporate water and in combination with shading, can help reduce peak summer air temperatures and reduce the amount of solar radiation resulting in cooler surfaces, which in turn, reduce the heat transmitted into buildings and the atmosphere. As a larger strategy to tackle heat spots, urban planning should aim at lowering energy use, reducing air pollution and greenhouse gas emissions besides decreasing storm water run-off. The combination of tree cover alongside concrete structures will not only reduce concrete heat build but also facilitate carbon storage and sequestration. As trees grow, they remove carbon from the atmosphere and store, or sequester, it. As trees die or deposit litter and debris on the ground, carbon is released into the atmosphere or transferred to the soil. The net effect of this carbon cycle is a substantial level of carbon storage in trees, vegetation, and soils. Green roofs are fast emerging as a technology that can help communities mitigate urban heat islands. A green roof is a vegetative layer grown on a roof-top. As with trees and vegetation elsewhere, vegetation on a green roof shades surfaces and removes heat from the air through evapotranspiration. Mechanisms such as these help reduce temperatures of the roof surface and the surrounding air. Green roofs can be installed on a wide range of buildings, including industrial, educational and Government facilities besides residences. Other measures that can be adopted include usage of bio- asphalt which is an asphalt alternative made from non-petroleum-based renewable resources. These sources include sugar, molasses, rice and corn besides potato starches and natural tree and gum resins. Bitumen can also be made from waste vacuum tower bottoms produced in the process of cleaning used motor oils, which are normally burned or dumped into landfills. Non-petroleum-based bitumen binders can be colored, which can reduce the temperatures of road surfaces and reduce the urban heat islands. With a variety of eco-friendly options available such as these, it is surprising that the problem of urban heat spots still adversely impacts the environment as well as quality of life of the communities. It is about time that the authorities strategically utilise the expertise and the technology available to counter heat spots and include measures to mitigate the same in the master plan for cities.
Posted on: Thu, 03 Apr 2014 07:56:51 +0000