It's Not Just the Rain: What Really Causes Mumbai's Monsoon Floods Every Year

Picture having a cup of chai (tea) by the Marine Drive with the drizzle moistening your hair, the first raindrops of the Mumbai monsoon are poetic. They tap against windows, soften the city’s skyline, and bring respite from the torrid summer heat. But as the rain gathers strength, this poetry turns into panic. Roads disappear under water, trains grind to a halt, and office-goers wade through ankle-deep and sometimes waist-deep, murky streets. Each monsoon, floodwaters return and, with them, the familiar disruption of life in one of the world’s biggest cities.

The outdated infrastructure, vanishing wetlands, and climate change — together have made monsoons in Mumbai worse with every passing year. And we have tried to break down the science behind it! 

1. Mumbai’s geography

To understand why Mumbai floods, you need to look at where it stands, quite literally. Originally a group of seven islands, the city was stitched together through centuries of land reclamation projects. Much of modern Mumbai sits barely above sea level, and some neighbourhoods, like parts of Dadar, Mahim, and Kurla, are below the high tide mark.

When the tides rise, the sea tries to reclaim what was once its own. And if heavy rain hits at the same time, the water has nowhere to go, thus leading to floods.

2. Drainage that is stuck in the past

Mumbai’s underground stormwater drainage system dates back to the British era, designed to handle just 25 mm of rain per hour. That might have worked in 1900, but it does not work in 2025.

In the early 1990s, a major upgrade plan called BRIMSTOWAD was proposed to overhaul the system. Despite being ambitious and expensive, for years, it barely moved forward. Political delays, funding gaps, and red tape meant that by the time Mumbai faced its worst floods, the city was still depending on century-old drains.

Even today, in many areas, storm drains are clogged with plastic waste, debris, and silt. And in places where upgraded pumps exist, they are often not turned on in time.

3. Mangroves: Natural flood defence is now bulldozed

For decades, Mumbai’s mangroves acted as natural sponges, soaking up excess rainwater, filtering pollutants, and slowing down tidal surges. They formed a protective barrier between the sea and the city.

But development has taken a toll. Over 40 percent of the city’s mangroves have vanished in the past few decades, often cleared illegally for housing projects, dumping grounds, or infrastructure. This is a practical loss with visible after-effects. Without them, water that once had room to spread out now floods homes and streets.

4. Climate change: Making the situation worse

It is getting hotter in the Arabian Sea, and even though it might sound distant, it is changing. Think of it like this: a warmer sea works like a giant steam machine. It sends up more moisture into the air, which then turns into heavier and more sudden rain.

Earlier, Mumbai’s rains used to come in steady waves. Now, it often pours all at once, like the sky has opened up. Climate scientists say these intense rainstorms have tripled since the 1950s, and they’re only going to get more common.

5. Poor urban planning

Modern Mumbai has been built with little regard for how water moves. Creeks have been narrowed, wetlands filled, and stormwater channels blocked by unplanned construction. In some areas, slums and high-rises sit directly on top of natural drainage routes.

Even newer developments, meant to be smart and flood-resilient, often ignore ground realities. Developers pave over absorbent land with concrete. Roads lack proper slope, and the footpaths are too high. This is the reason why water stays where it falls.

So what can we do?

There is no single fix that will stop Mumbai from flooding. But there are a handful of critical actions that, together, can make a real difference:

1. Protect what nature gave us

Mangroves, wetlands, and natural creeks act like sponges during heavy rain, absorbing water and slowing floods. But years of unchecked construction have eroded these defences. Strict enforcement of conservation laws and restoration, where possible, is urgent.

2. Predict, prepare, and respond

Flooding does not have to catch a city off guard. With better use of real-time weather data, advanced forecasting, and early warning systems, authorities can alert communities sooner and coordinate emergency responses more effectively.

3. Rethink how we build the city

Too many developments in Mumbai ignore how water moves through the land. Future urban planning must consider natural drainage patterns, allowing water to flow, soak, and drain, instead of blocking it with concrete at every turn.

Edited by Saumya Singh