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Indian Summer Monsoon Rainfall (ISMR) Study


A recent study published by Advancing Earth and Space Sciences (AGU) explores the geographical trapping of synchronous extremes during the Indian Summer Monsoon Rainfall (ISMR) from 1901 to 2019. The findings indicate significant alterations in the ISMR due to global warming, emphasizing the consistent presence of interconnected extreme hubs in Central India. This suggests a geographical concentration of concurrent extreme rainfall events in the region.


GS I: Geography

Dimensions of the Article:

  1. Indian Summer Monsoon Rainfall (ISMR) Trends: Insights from a Century
  2. Implications for Forecasting Synchronized Extreme Rainfall in India
  3. Factors Influencing the Indian Monsoon

Indian Summer Monsoon Rainfall (ISMR) Trends: Insights from a Century

Consistent Geographical Concentration:
  • Overview:
    • Despite heightened variability in ISMR over the last century, synchronous extreme rainfall events consistently concentrate in a specific geographical region – Central India (CI).
  • Unchanged Corridor:
    • The identified corridor, spanning from parts of West Bengal and Odisha to parts of Gujarat and Rajasthan, has remained unchanged from 1901 to 2019.
  • Stable Pattern:
    • This stability denotes a consistent pattern of synchronized extreme events within the identified region, despite the overall increased variability.
Persistent Network of Extreme Hubs in CI:
  • Local Connections:
    • A persistent network of highly interconnected extreme rainfall hubs exists in CI.
  • Local Synchronization:
    • These hubs demonstrate strong local connections, emphasizing the enduring synchronization of extreme events in CI over the long term.
Relation to El Niño and La Niña:
  • Forecast Dependencies:
    • India’s monsoon forecasts heavily rely on the relation to El Niño and La Niña phenomena, showing accuracy approximately 60% of the time.
  • ENSO Correlation:
    • Indian Rainfall events exhibit correlation with El Niño Southern Oscillations (ENSO), with stronger synchronization during robust El Niño periods and less during La Niña conditions.
Insights for Risk Management:
  • Despite Increased Variability:
    • Despite the growing complexity of ISMR, recognizing the persistent nature of extreme rainfall synchronization in CI provides valuable insights for predicting synchronous extremes.
  • Implications:
    • This knowledge is crucial for developing effective adaptation strategies and risk management during the monsoon season.

Implications for Forecasting Synchronized Extreme Rainfall in India

  • Challenge to Global Warming Notion:
    • Despite assumptions that global warming eradicates stationary elements, the Indian monsoon’s ability to synchronize heavy rain events challenges this belief.
  • Persistence of Consistent Patterns:
    • Certain patterns, like synchronized extreme rainfall events along specific corridors, persist even amid climate change.
  • Identification of Geographic Corridor:
    • The identification of a geographic corridor, especially the mountain ranges along the west coast and across Central India, as a trapping zone for synchronized extreme rainfall events, provides a crucial insight.
  • Enhanced Forecast Understanding:
    • This insight enhances understanding of how and where these events occur, contributing to more accurate forecasts.
  • Optimizing Existing Models:
    • The research suggests that improving forecasts doesn’t necessarily require increased model resolution or higher computational costs. Instead, understanding synchronization dynamics within existing models could lead to more accurate predictions.
  • Strategic Shift in Forecasting:
    • The findings highlight a strategic shift in forecasting approaches, emphasizing the importance of synchronization dynamics.
  • Vital for Risk Reduction:
    • Accurate forecasts of large-scale extreme rainfall events are crucial for minimizing risks across sectors like agriculture, water management, energy, transportation, and public health.
  • Refining Risk Reduction Strategies:
    • The findings offer an opportunity to refine risk reduction strategies at a smaller scale, leveraging better forecasts for preparedness and mitigation.
  • Leveraging India’s Modelling Capacity:
    • The study underscores India’s strong modelling capacity and computational resources, positioning the country well to exploit this potential for better forecasting.
  • Minimizing Impacts on Various Sectors:
    • By delving into synchronization dynamics and optimizing forecasts, there is potential to minimize the impacts of extreme rainfall events on various sectors.

Factors Influencing the Indian Monsoon

Role of the Himalayas:
  • Mechanism:
    • The Himalayas play a crucial role in the formation of monsoon winds in India.
    • During summer, rapid heating of the Indian subcontinent creates a low-pressure system.
    • The Himalayas act as a barrier, preventing cool, dry air from the north and drawing in warm, moist air from the Indian Ocean.
Impact of the Thar Desert:
  • Rain Shadow Effect:
    • The Thar Desert, also known as the Great Indian Desert, is a significant factor.
    • It acts as a rain shadow for the Bay of Bengal branch, receiving little rainfall due to the Aravalli Mountain range.
    • The Arabian branch, moving parallel to the Thar Desert, also leads to minimal rainfall, impacting agriculture and the local economy.
    • Hot, dry air creates a low-pressure zone, drawing moisture-laden winds from the Indian Ocean, causing heavy rainfall in northwest India.
Contribution of the Indian Ocean:
  • Interaction with Low-Pressure System:
    • The Indian Ocean contributes significantly to monsoon winds.
    • The warm, moist air from the ocean interacts with the low-pressure system over the Indian subcontinent, contributing to the formation of monsoon winds.

-Source: The Hindu

February 2024