How to absorb rainwater – what Indian cities need to learn

For Mumbaikars, there’s a grim familiarity to the crisis unfolding in the city that has taken at least seven lives in the past five days. Relentless rain has submerged roads, inundated homes in low-lying neighbourhoods, delayed commuters, and forced educational institutes to suspend classes and examinations. The India Meteorological Department has warned of more rain over the next three days, raising fears of further flooding in the country’s financial capital.

Built on what were once seven islands, much of Mumbai is land reclaimed from the sea. Large parts of the metropolis lie only a few metres above sea level. Urban expansion has disrupted the city’s intricate hydrological network — creeks, salt pans and wetlands that used to absorb the rain before gradually releasing it into the sea. During every spell of intense rainfall, water tries to flow along the erstwhile water channels — that explains the regular inundation of areas like Hindmata, Kurla, Sion and parts of the western suburbs. After the devastating floods of 2005, the city’s administrators did initiate meaningful changes — pumping stations were installed, and forecasting systems strengthened. However, despite being revamped on large stretches, Mumbai’s drainage network is ill-equipped to deal with short but intense bursts of rainfall. The storm-water system relies on gravity to empty water into the sea. This mechanism comes apart when heavy downpour coincides with high tide, like in the past few days — the seawater rises above the drainage outfall and pushes it back.

The predicaments of Mumbai’s administrators are similar to those of their counterparts in several parts of the world — it’s increasingly becoming apparent that improving drainage systems alone does not offer security against climate vagaries. China’s Sponge City policy, adopted after the Beijing floods of 2012, tries to address this challenge by enhancing the water retention capacity of the country’s urban centres — replacing concrete pavements with permeable ones, restoring urban wetlands and creating artificial lakes to store rainwater. Planners in the Netherlands’ low-lying cities have also been innovative. Instead of only strengthening traditional flood defences, they have created everyday amenities like water squares — these collect water during episodes of extreme rain, while doubling as recreation centres during the dry season — and incentivised the construction of green roofs. Mumbai’s municipal agency, too, has lake restoration projects on its agenda. However, “blue-green infrastructure” remains largely a niche concept in most parts of India, including in its financial capital. The country’s urban centres need housing, transport, commercial districts and modern infrastructure. The task for planners and administrators is to design them in a manner that does not render cities defenceless against extreme weather.