Monsoon in India: Impact, Progress, and Variability (GS Paper 1, Geography)
Introduction
- The southwest monsoon is a pivotal weather phenomenon for India, influencing its climate, agriculture, and economy.
- This seasonal reversal of wind patterns brings the majority of India's annual rainfall, critical for sustaining agriculture and water resources nationwide.
Monsoon Onset and Progress
- Onset: Traditionally, the southwest monsoon arrives over the Andaman Sea by the third week of May and advances into mainland India through Kerala by June 1st. The Indian Meteorological Department (IMD) monitors specific criteria such as rainfall, wind patterns, and Outgoing Longwave Radiation (OLR) to officially declare its onset.
- Progress: Post-onset, the monsoon progresses northward, covering the entire Indian subcontinent in approximately six weeks. It advances in surges, initially moving swiftly over central India before slowing down as it reaches northern regions by late June.
Monsoon Retreat
- Withdrawal: The retreat of the monsoon marks the transition from the rainy season to the dry winter period. It begins from the northwestern states of India around early September and withdraws completely from the country by early October. Unlike its onset, the retreat is a gradual process, with residual rainfall persisting in southern and northeastern regions into October.
Factors Affecting Monsoon
- Inter-Tropical Convergence Zone (ITCZ): The northward shift of the ITCZ triggers the onset of monsoon rains over the Indian subcontinent, marking the commencement of the rainy season.
- Monsoon Trough: The formation of a thermal low-pressure area over northwestern India facilitates the progression of monsoon winds and contributes to sustained rainfall across the region.
- Climate Oscillations: Global climate phenomena such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) exert significant influence on monsoon variability. El Niño events typically suppress monsoon rainfall, while La Niña events enhance it, illustrating the complex interplay of ocean-atmosphere interactions on regional weather patterns.
Monsoon Variability
- Year-to-Year Variation: Known as interannual variability, this phenomenon leads to fluctuations in monsoon rainfall over successive years. The variability is influenced by factors like ENSO phases (El Niño and La Niña), IOD phases, North Atlantic Oscillation (NAO), and Pacific Decadal Oscillations (PDO), which collectively determine the strength and distribution of monsoon rainfall across India.
- Impact of Synoptic Systems: Alongside the monsoon trough, the presence of cyclonic circulations, low-pressure systems, and depressions significantly contribute to localized variations in rainfall intensity and distribution.
Analysis and Forecast
- Seasonal Outlook: The IMD provides forecasts based on comprehensive climate models and observations, predicting the quantum and distribution of monsoon rainfall for the upcoming season. Forecasts indicating above-normal rainfall are often linked to prevailing La Niña conditions and a positive phase of the IOD, historically associated with enhanced monsoon activity over the Indian subcontinent.
- Long Period Average (LPA): IMD benchmarks seasonal rainfall against the Long Period Average (LPA) derived from historical data spanning several decades (typically 1971-2000 or 1971-2020). An LPA of 880 mm serves as a reference to assess the adequacy and distribution of monsoon rainfall across different regions of India.
Conclusion
- Understanding the dynamics of the Indian monsoon is crucial for agricultural planning, water resource management, and disaster preparedness across the country.
- As a lifeline for India's agrarian economy, the monsoon's variability necessitates adaptive strategies and resilience-building measures to mitigate risks associated with both excess and deficit rainfall scenarios.
- This comprehensive overview underscores the monsoon's pivotal role in shaping India's socio-economic landscape, emphasizing the need for continuous monitoring, scientific research, and community engagement to harness its potential while mitigating its adverse impacts on vulnerable populations and ecosystems.
