The Indian Meteorological Department recorded 111.8 mm of rainfall at its Santacruz station in Mumbai and 74.4 mm in Colaba between 8.30 am and 5.30 pm on Friday. This is nowhere near the record 944 mm Santacruz recorded over 24 hours on July 26, 2005, after a freak cloudburst inundated almost the entire city. Colaba recorded only 73 mm of rain that day.

Friday's rains affected much of the city. Houses were inundated, thousands of commuters were stranded, international flights were cancelled and the vital local train services were very sporadic.

Rainfall even slightly above average can affect the city so badly because of its poor drainage systems – which are under the charge of the Brihanmumbai Municipal Corporation, which has been run uninterrupted for two decades by the Shiv Sena and Bharatiya Janata Party.

Evading responsibility

So it made sense that Shiv Sena executive Uddhav Thackeray and his son Aditya gave several interviews trying to escape responsibility for the poor state of the city's infrastructure. Both claimed that Mumbai had received the equivalent of ten days of rain in one day and had been caught unawares by the volume of water. This kind of downpour, they said, was unusual for the city.

The Thackerays have a reason for their prevarication. Only on Wednesday, the municipal corporation inaugurated two pumping stations in South Mumbai to help storm water drainage that together cost a little over Rs 200 crore. Both were largely ineffective.

The younger Thackeray also attempted to shuffle off some blame to the railways. The reason the train lines were down, he said, was because the railways had not managed its drainage channels, perhaps forgetting that the city’s railway lines do not exist in a vacuum.

“A lot of the railway line is not with the BMC,” Thackeray told the NDTV, describing the day as a national calamity situation.

At the very least, the Thackerays are guilty of bad maths. Even if you generously allow for 300 mm of rain in the last 24 hours, the average daily rainfall in Mumbai during the monsoon is only 60 mm. At worst, the city received five times its normal daily rainfall.

It will get worse

If Friday seemed bad, it might have been because as with every year, the media chose to send reporters to the traditional low-lying areas such as Kalina and Khar. While services and houses were indeed impacted, it was nowhere near the scale suggested by news channels.

However, that does not mean the future is particularly bright for the city.

A study by scientists at the Indian Meteorological Department says that extreme rainfall events are only going to become more common over the Konkan and that the gaps between rainfall days will increase.

Pulak Guhathakurta, OP Sreejith and PA Menon studied metreological data from 1901 to 2005 from stations across the country to show that one-day extreme rainfall events have increased over the west coast, parts of central India and the north. At the same time, almost the entire country has seen a decrease in heavy rainfall days.

Impact on Mumbai

The Mumbai municipal corporations pet BRIMSTOWAD project to build stormwater drains is almost certainly a failure, largely because of sub-standard contractors, as a scathing Comptroller and Auditor General report pointed out in December, referring to the city’s two new pumping stations.

Already, the city’s natural drainage systems – mangroves, mudflats and salt pans – are rapidly disappearing legally and illegally to construction.

Last June, the Congress state government decided to open up 71 acres of the salt pans at Wadala, ostensibly to rehabilitate slum dwellers and centralise government offices. Meanwhile, mangroves and mud flats mysteriously shrink over the months or are used as informal dumping grounds. A study conducted by Mumbai University in 2012 showed that 54.7 sq km of land had been created in the city since 1990 by illegally destroying mangrove forests.

Coastal zone regulations

Another area for concern is the coastal regulation zone. This zone marks the boundary along the coast beyond which no development is allowed. An unencumbered coast helps rainwater to drain smoothly. Though the Central government issued the Coastal Regulation Zone notification in 1991, the Maharashtra government took seven years to submit a map of its coastal zones, including that of Mumbai. During this time, at least 500 illegal buildings sprang up on coastal land, blocking natural drainage. In 2011, the state shifted the no-development zone from 200 metres to 100 metres away from the coastline.

Earlier this month, the Union environment ministry cleared the proposal for a coastal road to link Kandivali in the western suburbs to Nariman Point 35 km to the south. Apart from its more tangible impact on the social fabric of the city – the government report on the road classifies Koliwadas inhabited by traditional fishing communities as eyesores – the impact of the reclamation that the road will entail has not been calculated. In recent decades, reclamation projects in the city, notably the Bandra-Kurla Complex, have contributed significantly to waterlogging, .

One point of relief was that Union Environment minister Prakash Javadekar announced at the time of the clearance that the road would not mean the coastal regulation zone would be altered in any way.