Kolkata Drenched: Third-Highest Rainfall in Decades — Cloudburst or Not? IMD Explains

Kolkata, 23 September 2025 — The city of joy woke up to a nightmare on Tuesday. Between late Monday night and early Tuesday morning, Kolkata received 251.4 mm of rainfall in just 24 hours, ending at 8:30 AM. According to the India Meteorological Department (IMD), this was the third-highest single-day rainfall in September after 1978 and 1986.

For the people of Kolkata, the day felt historic. Streets were flooded. Trains, flights, buses, and even the Metro came to a halt. Pandals built for Durga Puja were damaged. Shops, homes, and schools filled with water. In many areas, electricity was cut off.

But was this disaster a cloudburst? Many citizens believed so because of the sudden heavy downpour. The IMD has now given a clear explanation.

Historical context of rainfall in Kolkata

Heavy rain is not new to Kolkata. The city has witnessed record rainfall several times in its history. But what happened this time has placed itself in the record books.

• On 28 September 1978, Kolkata received 369.6 mm of rain in a single day. This remains the all-time highest in September.
• On 26 September 1986, the city saw 259.5 mm of rainfall in 24 hours.
• Now, on 23 September 2025, the city has faced 251.4 mm, which is just behind those two events.

If we compare all months, not just September, this event still ranks as the sixth-highest single-day rainfall in the last 100 years. That shows how rare this downpour was.

The timeline of the downpour

The rain was not spread evenly across the day. Instead, it came in short and violent bursts.

• The most intense spell was between 2:30 AM and 5:00 AM.
• Within this period, the single hour from 3:00 AM to 4:00 AM brought 98 mm of rain. That means nearly 10 cm of water fell in just one hour.
• By the time people woke up, several neighbourhoods were already under knee-deep water.

The IMD explained that a low-pressure system over Gangetic West Bengal and nearby areas pulled in a huge amount of moisture from the Bay of Bengal. This moisture rose into tall clouds reaching 5–7 km in the sky. When the clouds grew dense, they released massive amounts of rain in a short time.

Was it a cloudburst?

The word “cloudburst” often comes up whenever there is sudden, heavy rainfall. But there is a technical definition.

• The IMD defines a cloudburst as rainfall of 100 mm or more within one hour in a localised area.
• During this event, the maximum recorded was 98 mm in one hour.
• This was extremely close to the definition, but not enough to qualify.

So officially, IMD says this was not a cloudburst. Still, some experts call it “cloudburst-like rain” because the intensity was almost the same. For citizens trapped in flooded streets, the technical difference hardly mattered.

How the city was affected

The impact of the downpour was visible everywhere. Life in the city almost came to a stop.

1. Neighbourhoods hit hardest

• South Kolkata suffered the most.
  • Garia Kamdahari recorded 332 mm.
  • Jodhpur Park had 285 mm.
  • Kalighat saw 280 mm.
  • Topsia registered 275 mm.
  • Ballygunge reported 264 mm.
• North Kolkata also faced problems, though slightly less severe. Thanthania reported 195 mm of rain.

2. Transport breakdown

• The Metro services were disrupted as water entered underground sections.
• Many local trains were cancelled or delayed.
• Waterlogging at the airport affected flights, with several cancellations and diversions.
• Main roads were flooded, trapping buses, cars, and taxis. People had to wade through waist-deep water in some places.

3. Power cuts and safety hazards

• In many areas, electricity was switched off for safety.
• Sadly, at least 7–10 deaths occurred, most due to electrocution from live wires submerged in water.
• Several incidents of walls collapsing and tree falls were reported.

4. Durga Puja disruption

• With Puja only weeks away, many pandals and decorations were damaged.
• Organisers had to pump out water and rebuild parts of the structures.
• For shopkeepers and artisans, this meant heavy losses.

What the IMD said

IMD scientists explained the weather system clearly:

• A low-pressure area over the Bay of Bengal moved inland.
• The system carried huge amounts of moisture and created moisture convergence over Kolkata.
• Clouds rose up to 5–7 km, which is unusual and indicates high instability.
• This led to very heavy rainfall within a short period.

They also explained why it cannot be called a cloudburst. “The highest hourly rainfall was 98 mm, which is below the threshold of 100 mm. Therefore, this is not a cloudburst in official terms,” the department said.

What’s next in the forecast?

The immediate system is expected to weaken after a couple of days. But IMD has warned that another low-pressure system may form over the Bay of Bengal around 25 September. By 27 September, it could intensify into a depression.

This means South Bengal, including Kolkata, may continue to receive rain, though not as heavy as the 23 September deluge. Citizens have been asked to stay alert, avoid flooded areas, and follow weather updates.

Why such events matter

Events like this raise important questions about Kolkata’s readiness.

1. Drainage and infrastructure: The city’s drainage system cannot handle such intense rainfall in a short time. Waterlogging has been a long-standing issue.
2. Electrical safety: Electrocution deaths could have been prevented if power lines were better protected.
3. Climate change factor: Scientists say extreme rain events are becoming more frequent due to climate change. Warmer air holds more moisture, leading to heavier rainfall.
4. Urban planning: Encroachment on canals, wetlands, and water bodies makes flooding worse. The Adi Ganga canal, for example, is clogged and unable to drain rainwater effectively.

Conclusion

The rain of 23 September 2025 will be remembered as one of the city’s worst downpours in decades. Officially, it was not a cloudburst, but its impact was almost the same. For thousands of people, the technical label did not matter. They struggled through flooded homes, damaged roads, and darkened streets without power.

The incident highlights Kolkata’s fragile urban systems. With climate change bringing more unpredictable weather, the city must act. Better drainage, safe power systems, and advance warnings can save lives.

Kolkata is known for its resilience. But resilience should not mean suffering again and again. The lesson from this rainfall is clear — prepare better, act faster, and make the city safer before the next storm arrives.