In 1986, the Government of India in 1987 decided to designate February 28 as the National Science Day (NSD) to commemorate Prof Chandrasekhara Venkata Raman for his discovery of the Raman Effect on February 28, 1928, for which he was awarded the Nobel Prize in 1930.
Events on this day remind the importance of science inspiring people of all ages. This day attracts many young minds and motivates them to take up science as their career. The event is celebrated in schools, colleges, universities and other academic and scientific, technical, medical and institutions.
Life is unimaginable without the application of science. The art and science of designing the built environment is a rigorous and multidisciplinary profession. Building design and city planning revolve around a few basic principles of science.
The air temperature at the city centre is higher than that of the surrounding non-urban areas; so it looks like an island; and this phenomenon is called Urban Heat Island (UHI), which attracts attention as an environmental problem unique to urban areas. UHI is considered as a major problem in the 21st century posed to human beings as a result of industrialisation and urbanisation. No doubt, industrialisation and urbanisation improve our material lives and comfort; however, many problems are induced by these processes such as UHI, global warming and air pollution. UHIs have the potential to directly influence health and welfare of urban residents. Many people die each year due to extreme heat.
As urban areas develop, changes occur in their landscapes. Buildings, roads, and other infrastructure replace open land and vegetation. Surfaces that were once permeable and moist become impermeable and dry. These changes make urban regions warmer than their rural surroundings, forming an “island” of higher temperatures in the landscapes. On a hot, sunny summer day, roof and pavement surface temperatures can be hotter than the air, while shaded or moist surfaces —often in more rural surroundings — remain close to air temperature.
The local temperature is one of the major climatic elements to record the changes in the atmospheric environment brought by industrialisation, increasing population and massive urbanisation. However, the temperature trends in annual mean minimum temperatures reported in various countries across the world showed warming trends to be associated to the urbanisation process of the cities.
The urbanisation pattern in India is reflected by the trends of differences in annual mean minimum temperature of different cities. Research shows both Delhi and Mumbai are becoming UHIs with significantly different climates to their surrounding rural areas. Preliminary findings from the Delhi-based The Energy and Resources Institute (TERI) show temperatures in both cities have risen by 20C-30C in 15 years.
Atmosphere researchers have found that the massive amounts of heat produced by cities may be heating up rural areas 1,000 miles away. Scientists have long invoked the UHI effect to explain why cities are generally hotter than suburban and rural areas. More people, as well as more cars, houses, and paved surfaces, turn energy into heat.
In studies of ‘heat island effect’ generated by buildings, it was found that clusters of trees within the heat island can produce a localised drop in temperature by 2–30C. In terms of landscaping, the planting of trees and shrubs is encouraged with benefits that include a reduction in the heat island effect, solar shading in summer and protection from wind.
The heat island effect is due to the heat absorbed or given out by buildings and roads. There are several other causes of an UHI. These are changes in the thermal properties of surface materials and lack of evapotranspiration (for example through lack of vegetation) in urban areas. Materials commonly used in urban areas for pavement and roofs have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties than the surrounding rural areas. This causes a change in the energy balance of the urban area, often leading to higher temperatures than the surrounding areas.
Other causes of a UHI are due to geometric effects. The tall buildings in many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. Another effect of building is the blocking of wind, which also inhibits cooling by convection. Waste heat from automobiles, air-conditioning, industry, and other sources also contribute to the UHI. High levels of pollution in urban areas can also increase the UHI as many forms of pollution change the radiative properties of the atmosphere.
Throughout the daytime, particularly when the skies are free of clouds, urban surfaces are warmed by the absorption of solar radiation. Surfaces in the urban areas tend to warm faster than those of the surrounding areas. By virtue of their high heat capacities, urban surfaces act as a giant reservoir of heat energy.
Not all cities have a distinct urban heat island. Many communities are taking action to reduce UHIs. Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-coloured surfaces in urban areas, which reflect more sunlight and absorb less heat. A green roof is a roof of a building that is partially or completely covered with vegetation, planted over a waterproofing membrane. Green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation and helping to lower urban air temperatures and mitigate the heat island effect. The term green roof may also be used to indicate roofs that use some form of green technology such as solar thermal collectors or photovoltaic panels. Green roofs are excellent insulators during the warm weather months and the plants cool the surrounding environment. Air quality is improved as the plants absorb and convert carbon dioxide into oxygen. The cooling potential is also increased by planting street trees and open space planting.
Excessive heat in the urban environment can have serious negative impacts on the dwellers resulting in heat-stress and higher energy use. A widespread implementation of green technology provides additional benefits. These include savings to the building owners and occupants and to the community by reducing air temperatures, resulting in multiple benefits associated with cooler summertime air. Promotion of strategies for mitigating the UHI is a big concern for Government agencies, architects and planners. There should be a policy framework to reduce UHI effects. In order to promote measures appropriately, it is necessary to strengthen coordination between various measures and implement them systematically.
