Talking about the weather is serious business in Mumbai these days. Mumbaikars cannot understand why summers are getting hotter and drier, rains more intermittent and that November nip in the air turning sharper. And the meteorology department is giving them no clues.
In fact, the two city centres of the meteorology department are still recording normal Mumbai temperatures of 30-35° C. But in the course of his independent study, leading city naturalist Sunjoy Monga has come up with results starkly different. Using fairly precise instruments, he has recorded a high of 48° at Kandivili and Andheri, two of Mumbai's most densely populated areas. The reason for the stark discrepancy: the met centres are located in cool, unpolluted and uncrowded environs. They also follow global standardisations and are shade temperatures. Monga's measurements are in the open sunlight and closer to what the average Mumbaikar experiences.
Even without any actual change in the climate, says Thakur Prasad, director, Regional Meteorological Centre at Colaba, local factors considerably influence people's comfort level in the city. Prime among these is the heat island effect that's increasingly engulfing the city and rising each year.
The spatial variation of temperature generally shows that cities are warmer than the nearby surrounding areas. This is courtesy population concentration, industrial activity and dense built-up areas. The higher temperature regions in the interior of a city are known as heat islands. A significant difference has emerged between the mapping of urban temperatures done in '76 and the one Colaba Centre did in '97. The former showed warm pockets over Malabar Hill, Girgaum and Cuffe Parade in south Mumbai and a contrast of 11° in urban and rural suburbs, due to maritime influences.
But the city today has grown to cover 430 sq km. Dense industrialisation, ACs, traffic junctions, concrete and tar all add up to the heat islands, modifying temperature distribution. The tongue of warm air that extended from south Mumbai to Sion-Kurla in 1976 still exists but today splits into three branches roughly along the three suburban rail tracks. Heat islands are now located well within the city over Bhendi Bazaar, Jogeshwari and Thane in winter and Sion-Kurla, Chembur and Borivili too in summer. The hilly green lung of Mumbai—that includes the Virar and Powai lakes, Film City, Aarey colony, the National Park and the reserved forest area—shows a drop of up to almost 12° in winter.
Human comfort depends on three weather factors—temperature, humidity and wind speed. A good wind can bring temperatures down by 2-4°. But dense urban constructions obstruct the wind. They also deplete the city's green spaces. About 40 per cent of the region's mangrove cover has been depleted over the last two decades, and more in the last five years. Ironically, the Bandra-Kurla Complex has been developed by the Mumbai Metropolitan Region Development Agency (MMRDA) on several acres of mangroves under the Coastal Regulation Zone administered by the MMRDA itself.
Esselworld, that huge entertainment complex, has destroyed acres of mangroves as has the Royal Palm Golf Club. "Golf clubs may argue that they cover the place with grass, but they can't replace the multi-layered canopy of trees," says Debi Goenka of the Bombay Environment Action Group. The government hands over land under the slum rehabilitation scheme; in February, it generously handed out 1,000 acres of mangroves to another golf club along the Malad Creek. On the central line, large tracts of the National Park on the Thane end have been destroyed by bootleggers. As a result, Mumbai's open space (not necessarily green) ratio is probably the lowest in the world at 1 sq metre per person.Hong Kong, among the world's most densely populated cities, has eight times that; London has 15.
Monga has noticed several inexplicable changes in Mumbai in the last few years. Like the monsoon has long pauses in between rainy spells. Some flowering trees, like the flame-of-the-forest which blooms in March-April, has started blooming early. The number of migratory birds has gone up. The changes may be welcome but it's time Mumbai administrators woke up to this serious tampering with nature.