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Bay of Bengal Low Pressure Triggers Heavy Rains in Western Districts

Source:The Hindu ↗

Why It Matters

WBCS Prelims Geography often tests knowledge of West Bengal's climate, monsoon mechanisms, and district geography. This news event serves as a practical example of the Bay of Bengal's influence on the state's rainfall distribution.

Summary

A low-pressure system, originating as a deep depression over the Bay of Bengal and making landfall near Sagar Islands, has weakened into a depression as it moves toward Jharkhand. This movement is causing intense rainfall, thunderstorms, and gusty winds across the western districts of West Bengal. The active monsoon trough and significant moisture incursion from the Bay of Bengal are also triggering isolated heavy rains in the sub-Himalayan districts.

Key Points

  • A deep depression that crossed the West Bengal coast near Sagar Islands has weakened into a depression and is moving west-northwestwards toward Jharkhand.
  • The IMD predicted heavy to very heavy rainfall, along with thunderstorms and gusty winds, for several western districts of West Bengal, including Purulia, Bankura, and Paschim Bardhaman.
  • The sub-Himalayan districts of West Bengal, such as Darjeeling, Kalimpong, Alipurduar, and Jalpaiguri, are also expected to experience isolated heavy rain.
  • The severe weather is driven by an active monsoon trough and strong moisture incursion from the Bay of Bengal.

Important Terms

Monsoon Trough

An elongated low-pressure area from Pakistan to the Bay of Bengal during the southwest monsoon. Its position determines active or break monsoon phases in India.

UPSC context

Crucial for GS Paper I (Geography) and GS Paper III (Disaster Management) to understand India's spatial rainfall distribution and flood risks.

Source
Deep Depression

An IMD tropical cyclone classification for a low-pressure system with maximum sustained 3-minute surface winds between 28-33 knots (approx 52-61 km/h).

UPSC context

Important for GS Paper I (Climatology) and GS Paper III (Disaster Management) regarding cyclone formation stages and extreme weather early warnings.

Source
India Meteorological Department (IMD)

The principal agency under the Ministry of Earth Sciences responsible for meteorological observations, weather forecasting, and seismology in India.

UPSC context

Essential for GS Paper III (Disaster Management and Science & Tech) as the nodal agency for weather warnings and cyclone naming.

Source
Sagar Island

An island in the Ganges delta, West Bengal, located where the Hooghly River meets the Bay of Bengal. Famous for the annual Gangasagar pilgrimage.

UPSC context

Key for WBCS Geography of West Bengal, noting its location, vulnerability to cyclones, and cultural significance (Gangasagar Mela).

Source

Prelims Trap

Western plateau districts like Purulia and Bankura are immune to floods due to their drought-prone lateritic geography.

While generally drought-prone with low annual rainfall (100-125 cm), these districts frequently suffer sudden flash floods when Bay of Bengal depressions move west-northwestward.

Static Concepts Connected

Climatology & Indian Monsoon

What governs the movement and impact of monsoon depressions in Eastern India?

  • Monsoon Trough: Depressions generally move west-northwestwards along the active monsoon trough, dictating the spatial distribution of heavy rainfall across states like West Bengal and Jharkhand.
  • Moisture Incursion: Their sustained intensity as they travel inland depends heavily on continuous moisture supply drawn from the Bay of Bengal.
  • Landfall Weakening: Once they cross the coast, they gradually weaken from deep depressions into depressions due to surface friction and reduced moisture supply.
Geography of West Bengal

What are the core geographic characteristics of West Bengal's western districts?

  • Tropic of Cancer: The 23°30' N latitude passes directly through five districts, notably the western districts of Purulia, Bankura, and Paschim Bardhaman.
  • Plateau Fringe: They form the easternmost fringe of the Chota Nagpur Plateau, characterized by undulating topography and ancient crystalline rocks.
  • Lateritic Soil: The region is dominated by red and laterite soils with poor water-holding capacity, making it historically drought-prone despite occasional torrential downpours.

Cross-Topic Patterns

  • Lateritic soils and flash flood vulnerability

    The poor water infiltration capacity of laterite soils in Bankura and Purulia exacerbates surface runoff and flash flood risks when sudden monsoon depressions dump heavy rainfall over the plateau.

  • Sagar Island's dual geographic-cultural significance

    Beyond being a frequent landfall site for Bay of Bengal disturbances at the Hooghly estuary, Sagar Island frequently appears in static GK for the Kapil Muni Temple and annual Ganga Sagar Mela.

Expect a multi-statement Geography question mapping BoB depression pathways to WB's Tropic of Cancer districts and soil types.

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