publiceye Bangalore's green cover is being replaced by concrete structures. No wonder you are getting hotter under the collar
Mean maximum temperature increased by 3 degrees Celsius Rapid urbanisation blamed for rise in temperature
Bangalore: It is no figment of the nostalgic Bangalorean's imagination. Temperatures in the city are indeed rising, and it is official.
The monthly mean maximum temperature (that is, the average of all highest daily temperatures in a month) has been steadily on the rise. It has increased by two to three degree Celsius since 1960, according to G.S. Vijayaraghavan, Director of the Meteorological Centre. The highest maximum temperature in any given month has similarly risen by 1 to 2 degrees Celsius over the last four and a half decades.
March and April, Bangalore's hottest months, are only getting hotter.
The 20 years between 1967 and 1987 saw only three occasions when the maximum temperature for March rose beyond 35.5 degrees Celsius (approximately three degrees over what is considered the "normal" mean maximum for March).
In the following 20 years, between 1987 and 2007, there were 11 occasions when temperatures for March went above 35.5 degrees Celsius.
The figures for April of the last 40 years for maximum temperatures reflect the same trend.
Over the last 20 years, the temperatures went beyond 36.5 degrees Celsius (again, approximately three degrees over the normal maximum temp for April) on nine occasions, as opposed to only four such years in the two preceding decades starting 1967. "Temperature rise in the city is an undisputable phenomenon," says Mr. Vijayaraghavan. Even though natural weather variations are normal, especially in tropical countries, he attributes the temperature rise in Bangalore to the rapid urbanisation.
A simple example of human-induced weather change presents itself in the Centre's records to corroborate Mr. Vijayaraghavan's claims. The Centre's recording stations are placed in two different locations in the city, one in the centre and the other near the airport. The readings of these two thermometers are always 1 or 2 degrees different, with the one in the city centre recording higher temperatures consistently. On April 1, the temperature recorded on the centrally located Palace Road was 36 degrees Celsius, while the thermometer at the airport recorded 34.6 degrees Celsius.
This is a classic example of the "urban heat island" effect, says G.S. Bhat, Professor, Centre of Atmospheric and Oceanic Sciences. "Bangalore's green cover is being replaced by concrete structures that absorb solar radiation very rapidly."
Prof. Bhat adds that the impact of global warming on the city cannot be discounted either. "Weather patterns are changing across the globe. Summers are setting in early, and the winters are getting shorter. The changes in Bangalore's weather might also be a reflection of this larger phenomenon."
Vehicular pollution, with carbon dioxide and other green house gases that it generates, also has a role to play, says Mr. Vijayaraghavan. Approximately 1.5 lakh to two lakh vehicles are added to the city roads every year. "Carbon dioxide emissions trap heat, and whether you look at it at a micro level or at the global scale, it impacts climate," he says.
It is not just temperature rise, but rainfall patterns that have also been changing across the country according to Prof. Bhat.
Rain in Bangalore, which normally arrests rising temperatures, have also turned unpredictable.
The months of September and October are when Bangalore receives the highest rainfall in the year, about 195 mm and 180 mm respectively on an average.
Last year, however, Bangalore received only 45.3 mm in September (the lowest ever recorded in the city in half a century for the month) and 50.2 mm in October. "In fact, the last significant rains we had were in May last," observes Mr. Vijayaraghavan.
The Meteorological Centre expects rains in the second half of April, and though these summer rains will not quantitatively significant, they will be crucial in bringing temperatures down.
Heat island effect
Swathi Shivanand adds:
Environmentalist A.N. Yellappa Reddy seconds the "heat island effect" that steel, concrete and asphalted surfaces cause.
"It could increase temperatures even up to eight degrees," he says.
Building houses close to each other affects the movement of the wind and traps the heat, thereby affecting the ambient atmosphere. His suggestion is to have structures constructed with eco-friendly mud blocks.
"But if that is not possible, growing trees and shrubs will bring temperatures. If at least 30 per cent of the wall space is covered by the creepers and climbers, then it could bring down temperatures considerably."
Mr. Reddy warns that Bangalore's Metro Rail could cause "unbearable" amount of heat with all the usage of steel (1 lakh tonnes) and concrete if green cover is not used to mitigate the effect. Incidentally, the Bangalore Metro Rail Corporation is planning to plant ivy on all its bridges.
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