Five-Decade Extension of Southwest Monsoon in India

Recently, a research paper was published in the journal Mausam by scientists from the India Meteorological Department (IMD).

Key highlights of the Study

• Duration Extension
  • Increase in Duration: The Southwest Monsoon (SWM) season has extended by 1.6 days per decade from 1970 to 2020.
  • Total Rainfall Contribution: The SWM now contributes 79% of annual rainfall, an increase from the previous 75%.
• Delayed Withdrawal
  • Withdrawal Trends: Data from the past 14 years shows delays varying from 1 to 22 days, with 2019 withdrawal 22 days late and 2021, 19 days late. Considering the older monsoon start (Sept 1), 2019 withdrawal was 40 days late.”
• Changes in Rainfall Patterns
  • Impact on Research: The extended monsoon season alters long-term rainfall data, which is crucial for monitoring changing climate patterns.
  • Distortion of Metrics: Traditional SWM data (June 1 – September 30) no longer captures the entire monsoon season, complicating rainfall metrics for IMD.
• Agricultural Impacts
  • Effect on Crop Yields: Delayed withdrawal of monsoon influences Rabi crop yields, particularly for crops like rapeseed and mustard.
  • Improved Yield Correlation: When rainfall from the delayed monsoon is considered, yields for certain crops are found to be higher.
• Climate Change Connection: Climate change is a primary reason for the shifts in monsoon withdrawal and the extended season, as per statements from IMD in April 2020.
• ENSO Influence: The delayed monsoon withdrawal is closely linked to the ENSO phenomenon, which has an impact on rainfall distribution and agricultural outcomes.

About India Meteorological Department

• It is the primary government agency in India responsible for all matters related to meteorology, seismology, and other allied subjects.
• Established: 1875
• Headquarters: New Delhi
• Nodal agency: Ministry of Earth Sciences
• Mandate: To provide current and forecast meteorological information for optimum operation of weather-sensitive activities like agriculture, irrigation, shipping, aviation, offshore oil explorations, etc.

What is ENSO ?

• El Niño is a climate pattern that emerges from fluctuating ocean temperatures in the tropical Pacific, affecting weather patterns worldwide, especially monsoons. 
• It’s characterized by warmer-than-average sea surface temperatures in the central and eastern tropical Pacific Ocean, weakening the typical easterly trade winds.
• It can last for several months and recur irregularly every 2 to 7 years with three phases:
  • El Niño (warm phase)
  • La Niña (cool phase)
  • Neutral phase

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