It’s 4 p.m. in Kurla. The sky was clear at lunch. Then, over one cup of chai, the light turns grey, the first fat drops hit the awning — and by the time you’ve found your umbrella, the road outside your building has become a river. Not a puddle. A river, brown and moving, lapping at the second step of the shop next door. Scooters are stalled. A man has rolled his trousers to his knees and is carrying his shoes. It has been raining for one hour.
And the thought you have is the same one lakhs of Mumbaikars have every single monsoon:
“It was just one hour of rain. Why is my street underwater?”
It’s a fair question. Let’s answer it — properly, but simply. Simply enough that tonight, you could explain it to a ten-year-old.
What’s actually happening
Two things have to go wrong for a street to flood in an hour. First, too much water has to fall from the sky, too fast. Second, the water that falls has nowhere to go.
In Mumbai, both are now true at the same time. And here’s the honest part most people skip: one of those problems comes from the sky, and the other one we built ourselves. If we only tell you about one, we’re lying to you. So we’ll tell you about both.
Mumbai streets can flood when intense rain falls faster than water can drain or soak away. Image source: Shutterstock
Since when? Ask anyone over 50
Your grandmother will tell you Mumbai always had heavy rain — the monsoon is the city’s heartbeat. But she’ll also tell you something changed. The rain used to come steady, spread across days. Now it comes in bursts — the whole sky seeming to empty out in an hour or two, then nothing.
On 26 July 2005, Mumbai recorded 944 mm of rain in 24 hours, a benchmark flood event. Image source: Unsplash
She’s not imagining it. On 26 July 2005, Mumbai got 944 millimetres of rain in a single day — close to a year’s worth of rain for many Indian cities, in 24 hours. That day became the city’s benchmark for disaster. But the reason we still talk about it isn’t just the rain. It’s what the rain revealed.
Reason one: the sky (this is the climate part)
Here is the whole science, in one kitchen metaphor.
Think of the air above your head as a sponge. A warm sponge holds more water than a cold one. As we burn coal, petrol and gas, we are slowly warming the air — and a warmer sky is a bigger sponge. For every 1°C the air warms, it can hold about 7% more water. A fuller sponge, when it finally squeezes, dumps more at once. That is not a gentle drizzle anymore. That is a wall of water in an hour.
Short, high-intensity downpours are becoming more common, increasing urban flood risk. Image source: Unsplash
This isn’t a guess — India’s own scientists have measured it. Research published in Nature Climate Change found that extreme rainfall events over central India roughly tripled between 1950 and 2015. The India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM) — the country’s top weather bodies — now document that short, high-intensity downpours are becoming more common, and are a leading driver of urban flooding. In 2025, the IMD recorded a sharp rise in extreme-rainfall events, and rain-related disasters became the country’s deadliest climate hazard that year.
So the sky is delivering heavier bursts than it used to. That part is climate change — real, and measured. But it’s only half the story.
Reason two: the ground (this is the part we built)
Here’s the half that should make us all sit up: even if the rain hadn’t changed at all, Mumbai would still flood more than it did fifty years ago. Because we took away the places the water used to go.
Water is not stupid. It follows gravity, finds low ground, soaks into soil, collects in lakes, and drains to the sea through rivers and creeks. Mumbai was built on a natural drainage system — wetlands, mangroves, salt pans, and rivers like the Mithi that carried the rain out to the Arabian Sea.
Mumbai’s drainage can be overwhelmed when heavy rain coincides with limited natural absorption. Image source: Unsplash
Then we filled them in. Between the early 1990s and 2005, Mumbai and Thane lost roughly 40% of their wetlands — the natural sponges that soak up floodwater — to construction. The Mithi River, the city’s main storm drain, was narrowed by encroachment and building (including the Bandra Kurla Complex, raised on its wetlands) until the river shrank by about half. So in 2005, when the rain came, the choked river had no way to carry the water downstream — and it flowed into Mumbai’s streets instead.
And when you cover soil with concrete, the rain that used to soak in has nowhere to sink. Water that once seeped into the ground now sits on top of it. Twenty years and thousands of crores later, the Mithi is still choked and silted — and construction along it continues.
So picture it this way: the sky is now pouring more water into a bucket whose bottom we’ve been quietly sealing shut. More coming in, less able to get out. That’s your flooded street in one sentence.
Why “just one hour” is enough
Now the original question answers itself. Your street floods after one hour because the burst is heavier than it used to be (the sky), and because the water can’t drain or soak away like it used to (the ground). Mumbai’s own climate plan admits it bluntly: if a downpour like 26 July 2005 happened again, parts of the city would flood even with drainage upgraded to clear 50 mm an hour. The bucket simply isn’t big enough anymore — and the sky keeps getting fuller.
The kitchen-table version
Here’s how you explain it to your daughter tonight, watching the rain from the window:
Her: “Why is the road turning into a river? It only started raining!”
You: “Two reasons, beta. You know how a sponge can only hold so much water before it drips? The air over our city is like a giant sponge — and it’s getting warmer, from all the smoke from cars and factories. A warm sponge holds more water. So when it squeezes, it drops a lot at once.”
Her: “Okay, but where does the water go?”
You: “That’s the second reason. This whole area used to be marshes and a river that carried rainwater to the sea. We built roads and buildings on top of them. So now the water falls faster and has nowhere to go. That’s why the road floods.”
Her: “Can we fix it?”
You: “Some of it, yes. That’s the good part.”
What any one of us can actually do
This is where climate change stops being a headline and becomes something you have a hand in. None of these fixes the whole problem alone. Together, done by enough people, they change what one hour of rain does to a city.
Mumbai and Thane lost roughly 40% of their wetlands between the early 1990s and 2005. Image source: Shutterstock
At home
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Catch the rain that hits your roof. A basic rooftop rainwater-harvesting setup — a drum, a pit, some PVC pipe — sends terrace water back into the ground instead of into an already-overwhelmed drain. A Malad resident built a working version with IIT-Bombay’s help for a few thousand rupees; societies over 300 sq m in Mumbai are already required to have one, and the BMC offers a property-tax rebate for eco-measures like it.
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Make a soak pit or a rain garden. Even one un-concreted patch — gravel, a shallow pit, a few deep-rooted plants — lets water sink where it falls instead of running to the road.
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Keep your own lane’s drain clear. The nullahs flood partly because they’re packed with plastic. What your household drops into a drain in January is what backs up into your street in July. Don’t feed the choke.
In your building & neighbourhood
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Un-pave what you can. Push your society to swap solid cement for permeable paving, keep a green strip, or plant trees in the compound. A shaded, soil-covered plot both drinks rain and cools the building — one Mumbai homeowner’s 20-tree micro-forest keeps his house about 5°C cooler.
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Protect the water bodies still near you. A ward’s lake, pond or wetland is free, natural flood insurance. Ordinary residents — software engineers, retirees, schoolkids — have revived choked ponds and lakes across Indian cities, lifting the groundwater and giving the rain somewhere to sit. Join or start a lake-restoration group.
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Defend the mangroves. Mumbai’s remaining mangroves are the city’s coastal flood wall. Report dumping or destruction (Maharashtra has a mangrove-protection helpline), and back the citizen groups fighting their conversion.
Concrete surfaces and narrowed natural drains leave more rainwater sitting on Mumbai’s streets. Image source: Shutterstock
As a citizen
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Ask one question of every new project: “where will the rain go once this is built?” When a development comes up in your ward, that single question — asked by enough residents in writing — is how floodplains and natural drains actually get protected.
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Back “manage water where it falls,” not just “push it away.” Support local demands for wetland and river restoration alongside bigger drains. Experts are clear that concrete drainage alone can’t save a city that keeps erasing its natural sponges.
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Shrink the sky problem too. The “warm sponge” only shrinks when the world burns less coal, oil and gas. Your vote, your commute, your electricity use are small on their own — but they’re the lever on the size of that sponge.
Because here’s the whole point of this series: climate change isn’t only happening at summits and in scary reports. It’s happening on your street, in one hour of rain. And just as it got there through a thousand human choices, a thousand human choices are how we push back.
Real solutions we’ve covered at The Better India
This isn’t theory. People are already doing the fixes above — here are a few of their stories:
