More buildings, more rain

New research claims that the heat generated by steel, tar and concrete traps rain clouds over the city
Brace yourself for a really wet spoiler: new research shows that the alarming rate of construction in Mumbai, especially the suburbs, may be causing the heavy rains. This was found in a research conducted after the July 26, 2005 deluge in Mumbai, the results of which have been revealed recently. And if statistics are anything to go by, the city’s landscape is getting bigger and taller even as you read this.

Facts and figures

Every year, 5.5 crore square feet or 1,262 acres of construction is started in Mumbai, claims the Builders Association of India. In layperson’s term, this would mean that about 57 new Oval Maidans are added annually to the city landscape.

Yes, that would logically mean more residents, more traffic, more pollution and more profits for the builders and more rains as well according to the new research published in the Atmospheric Chemistry and Physics journal last month.

Suburb reality

A team of Indian and American scientists found out that urbanisation means more rain for the city. When we checked with the city’s Regional Meteorological Centre, in just two weeks of this month, the rain records for Colaba and Santacruz up till Saturday evening stood at 622.9 mm and 616 mm respectively.

Which means that the average of this year’s June month is much higher than the figures recorded for the entire month of June in the years 2006, 2005, 2004, 2002, 2000, 1999 and 1998.

“We were curious about why Santacruz received 944 mm in a single day (on 26 July, in 2005) while other areas in the city and outside, like Pune, hadn’t experienced the same. There was a low pressure aregion developing off the coast of the city and then, this moved toward the Western Ghats.

However, it’s our theory it didn’t progress further because of a barrier that kept the rain clouds over the city,” explains Dr Dev Niyogi, assistant professor in the Department of Earth and Atmospheric Sciences at Perdue University and the Indiana State climatologist. Niyogi is also the corresponding author of the paper titled ‘Effects of explicit urban land surface representation on the simulation of the 26 July 2005 heavy rain event over Mumbai, India’.

Invisible barrier

So what is this barrier? It’s an invisible barrier that possibly is a result of the urban heat island phenomenon – wherein, because of the presence of steel, tar and concrete, the surface area of a region rises rendering it warmer than the surrounding countryside.

“The influence of this land heat obviously takes place a few kilometres above the surface and hence we assume that this could have been the reason for the great amount of local rainfall on that day,” says Niyogi.

The urban heat island phenomenon is not an isolated theory nor is it a recent find. In a study in Indianapolis, Niyogi observed that approaching thunderstorms would split over the city, becoming more prevalent in the eastern and western parts where urban pockets were located.

Moreover, the effect of urbanisation on temperature was studied in London more than a century ago in 1870.

Mumbai builders tell Sunday MiD DAY that construction work has doubled in magnitude and reach in the last five years and can only get bigger

Different opinion

Detractors believe otherwise. “Monsoon depends on planetary movement. Micro level changes like change in local temperature won’t really affect the monsoon,” says Dr CV Bhadram, deputy director of the Indian Meteorological Department.

Seconding Dr Bhadram’s option is Dr R Krishnan, senior scientist in the climate and global modelling department of the Indian Institute of Tropical Meteorology in Pune. “Fifty years ago, when there wasn’t much development, we had periods of drought and heavy rain. There’s an in-built natural variability that governs monsoon patterns that can’t be predicted. Blaming the construction activity alone is questionable,” says Dr Krishnan.

Niyogi states that perhaps the consequence of urbanisation affecting national rain patterns may be debatable, what isn’t is its “affect on local rainfall in terms of its magnitude and intensity.”

(With inputs from Somita Pal)

When it rains, it pours

This year’s atmospheric patterns look grim. Scientists are currently debating whether 2008 will be an Indian Ocean Dipole year or a year of an IOD event. IOD is a climate mode that occurs inter-annually in the tropical parts of the Indian Ocean.

“A team of scientists from Japan strongly supports this theory wherein a positive IOD would result in very cold ocean temperatures off the coast of Sumatra in Indonesia. This in turn, results in good (read heavy) monsoons in India,” says senior scientist Dr R Krishnan.

Years of research have shown that global ocean and atmospheric activity have much effect on the Indian subcontinent’s showers. For example, the El Niño phenomenon in the Pacific Ocean, that largely affects the continents of North and South America, notably coincides with drought periods in India like in 2004.

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