Heavy rainfall in Kolkata caused by El-Nino

Key Driving Factors in South Bengal

1. Extended Dry Spells & Intense Convective Buoyancy

• During El Niño conditions, large-scale downward atmospheric motion over the western Pacific and eastern Indian Ocean suppresses the formation of persistent low-pressure systems.  

• This leads to prolonged rainless intervals and higher-than-normal ambient temperatures across Kolkata and surrounding districts.

• The resulting local surface heating creates intense convective buoyancy—heating air rapidly near the ground, forcing it to rise vertically and build massive cumulonimbus cloud columns.

2. Sudden Bay of Bengal Moisture Incursions

• Despite weak regional monsoon currents, Kolkata's proximity to the Bay of Bengal allows massive pulses of warm, moisture-laden maritime air to be drawn inland.

• When this sudden surge of atmospheric moisture collides with the unstable, super-heated air over South Bengal, it acts like a powder keg, releasing localized downpours within a short window rather than steady, multi-day drizzles.

3. Local Cloudburst-like Deluges

• Instead of the traditional monsoonal pattern—steady, continuous showers spread across several days—El Niño distorts the distribution.  

• Rainfall manifests as short, hyper-concentrated clusters. A single storm can dump 100–300+ mm of rain in just a few hours over specific urban pockets, overwhelming drainage networks and causing flash waterlogging.