Kolkata Cloudburst: Causes, Impact, and Climate Implications

On September 23, 2025, Kolkata experienced an unprecedented weather event—a cloudburst that led to the heaviest rainfall in 37 years. Between 11:30 PM on September 22 and 8:30 AM on September 23, the city received over 251 mm of rain, overwhelming drainage systems and causing widespread flooding.

The Impact on Kolkata

The cloudburst resulted in severe waterlogging across several areas, including Salt Lake, New Town, Sector V, and Rajarhat Gopalpur. In Sector V, known for its IT offices, knee-deep water in inner lanes significantly affected physical office attendance, which dropped to around 30%. Despite the disruption, most IT companies swiftly transitioned to work-from-home modes, minimizing work impact.

The torrential rain also led to the tragic loss of at least 10 lives due to electrocution and other rain-related incidents. Additionally, 30 flights were canceled, and 42 were delayed, severely disrupting air travel. Public transport, including metro and train services, was also paralyzed, and schools were closed to ensure the safety of students.

Understanding Cloudbursts

A cloudburst is a sudden, intense rainfall event, typically producing more than 100 mm of rain in an hour. These events are often triggered by atmospheric instability, where warm, moist air rises rapidly, condenses, and releases large amounts of rain over a short period. In Kolkata’s case, a dense cloud formation with a height of 5–7 km led to the cloudburst-like rain.

Rising Frequency of Cloudbursts in India

The Kolkata incident is part of a troubling trend of increasing cloudbursts across India in 2025. Earlier this year, a cloudburst in Uttarkashi, Uttarakhand, on August 5 resulted in flash floods, killing at least five people and leaving over 50 missing. Similarly, on August 14, a cloudburst in Kishtwar district, Jammu & Kashmir, led to 68 deaths and over 300 injuries.

Experts attribute the rising frequency of cloudbursts to several factors:

• Climate Change: Global warming increases atmospheric temperatures, enhancing the capacity of air to hold moisture. This leads to more intense and frequent rainfall events.
• Urbanization: Rapid urban development, especially in flood-prone areas, reduces natural water absorption, leading to increased surface runoff and flash floods.
• Deforestation: Loss of forests disrupts the natural water cycle, contributing to increased runoff and reduced water retention in the soil.

Conclusion

The September 23 cloudburst in Kolkata serves as a stark reminder of the urgent need for climate resilience and disaster preparedness. As extreme weather events become more frequent, it is crucial for authorities to invest in infrastructure improvements, early warning systems, and sustainable urban planning to mitigate the impacts of such disasters. Public awareness and community preparedness are equally important in building resilience against future climate-related challenges.