Many Indian districts saw a half of seasonal rainfall in 24 hours

Many Indian districts saw a half of seasonal rainfall in 24 hours

Subject :Geography

Section: Climatology

Context:

• The monsoon has been delayed this year and has not yet met its quota for June.

Details:

• However, many parts of the country witnessed heavy and erratic rainfall on June 25 and 26, accounting for around half of the total rainfall for the monsoon season.
• Some districts in India received 50 per cent or more of the season’s total rainfall in a single day in a few hours on June 25 and June 26, leading to a flood-like situation.
• Excessive rainfall in a few hours of a single day can also be fatal and is a clear sign of climate change.

Unusual rainfall across different regions of India:

• Bijnor district in Uttar Pradesh received 92.6 mm of rainfall between 8 am and 10 am on June 25, or ‘heavy rainfall’ as per IMD classification.
• Suburban areas in Mumbai in Maharashtra recorded ‘extremely heavy rainfall’ of 176.1 mm on June 25.
  • According to the IMD, rainfall recorded in the range of 125.5 to 244.4 mm in a day is considered extremely heavy rainfall. 
• Deogarh district of Odisha recorded 106.3 mm of rainfall on June 25. This was 1,419 per cent more than the normal rainfall average of 7 mm for the day.
• Kathua district in Jammu and Kashmir recorded 107.4 mm of rainfall — 2,287 per cent more than average.
• Mahasamund and Raipur districts of Chhattisgarh also received rainfall of 90.8 and 82.1 mm.

Minicloudbursts:

• Continuous rainfall of more than 50 millimetres (mm) for two hours is classified as a mini cloudburst according to the IMD.
• Many districts in several parts of the country witnessed mini cloudbursts on June 25 and 26.
• Cloudburst:
  • According to the IMD, 100mm of rain in an hour is called a cloudburst. They usually occur over a small geographical region of about 20 to 30 sq. km.

Rainfall classification as per the IMD:

Major factors affecting heavy rainfall:

1. Monsoon weather system

• Monsoon trough, Cyclonic Circulation, Low-Pressure Area, Depression, Cyclones etc.
• West coast offshore Trough.

2. Interaction of Mid-latitude systems with Monsoon Circulation:
3. Other Weather systems:

• Western Disturbances
• Pre Monsoon thunderstorms in association with Easterly/Westerly trough, Wind discontinuity, cyclonic circulations.

4. Northeast monsoonal system:

• Easterly waves, Trough, Low-pressure area, Depression, Cyclone.

5. The orographic uplifting of moist air

Steps for Monitoring and Prediction of Heavy Rainfall:

1. Analysis of causative weather system (genesis, evolution, characteristics & dissemination).
2. Analysis of current weather system based on surface, RADAR and Satellite observations.
3. Comparison of this analysis with model analysis.
4. Comparison of model diagnosis & prognosis and hence prediction of heavy rainfall for next five days.
5. Development of objective consensus based NWP models using decision support system about occurrence and intensity of rainfall.
6. Development of subjective consensus among forecasters through video conferencing system through knowledge, experience and expertise.
7. Final consensus forecast on occurrence and intensity of heavy rainfall by modulating objective consensus with subjective consensus.
8. Warning bulletin, product generation, presentation and dissemination.