Mini-cloudbursts on the Rise

GS1/GS3 – Geography & Disaster Management

Context
  • IMD Director-General Mrutyunjay Mohapatra clarified:
    • No “increasing trend” in cloudbursts in India.
    • Cloudbursts remain “impossible” to forecast.
    • However, “mini-cloudbursts” (localised but intense rainfall events) are increasing in frequency.
Key Highlights from IMD Update
  • Monsoon 2025 performance (till Aug 31):
    • 6% above normal rainfall (70 cm usual for June–Aug).
    • September forecast: 9% above normal (avg. 16.7 cm).
    • Regional trends:
      • Northwest India (Uttarakhand, UP, Punjab, Haryana, Delhi, Rajasthan, J&K): 26% above normal.
      • Central India: +8.6%.
      • Southern Peninsula: +9.3% (3rd highest since 2001).
      • Eastern & Northeastern India: -17% deficit (despite being the wettest monsoon bloc).
  • Extremes in 2025:
    • 700+ heavy rainfall events (>20 cm/day) in August 2025 (2nd highest since 2021).
    • August rainfall in North India (26.5 cm) – highest since 2001.
  • Reason for extremes:
    • Confluence of Western Disturbances (from the Mediterranean) + Bay of Bengal monsoon systems → triggered episodes of intense rains in Himachal, J&K, Uttarakhand.
  • Long-term trend:
    • Since 1980, an increasing rainfall trend in September has been observed.
What is a Cloudburst?
  • A sudden, intense rainfall event (≥100 mm/hour over a localized area, usually <20–30 sq. km).
  • Often occurs in hilly terrains due to orographic lift (warm moist air forced upwards by mountains → rapid condensation → heavy downpour).
What is a Mini-cloudburst?
  • No standard IMD definition, but refers to smaller-scale extreme rainfall events (typically <100 mm/hour but still destructive).
  • Increasingly reported in urban and peri-urban areas due to local convective activity and urban heat island effect.
Why are Cloudbursts Difficult to Predict?
  • Scale issue: They occur in micro-geographic areas.
  • Require real-time, high-resolution radar and satellite data, which current IMD forecasting models cannot fully capture.
Vulnerable Regions in India
  • Himalayan States: Uttarakhand, Himachal Pradesh, J&K, Northeast.
  • Urban areas: Mumbai, Bengaluru, Chennai (due to drainage congestion).
Role of Western Disturbances
  • Extra-tropical storms originating in the Mediterranean Sea.
  • Travel eastwards, bringing sudden rainfall/snowfall in Northwest India.
  • Intensify when interacting with monsoon systems from Bay of Bengal → trigger extreme rain events.
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