Syllabus: GS-I: Climate change

Why in the News?

The northeast monsoon (NEM) arrived four days early over Tamil Nadu in October 2025, marking the second consecutive year of early onset. This follows a year (2024) when Tamil Nadu recorded 33% above-normal rainfall during the same season. Meteorological agencies anticipate a similar pattern this year as well.

More About the News

• While traditionally considered a boon for rain-dependent regions like Tamil Nadu, climate change has altered the dynamics — with rain becoming more erratic, intense, and localised, resulting in urban flooding, waterlogging, and crop damage. 
• The phenomenon also raises inter-state water management concerns, particularly between Kerala and Tamil Nadu over the Mullaperiyar Dam during overlapping monsoon spells.
• This situation underscores the need to rethink the long-held notion that “excess rain is always good.”

About the Northeast and Southwest Monsoons

1. Southwest Monsoon (SWM) – The Summer Monsoon

• Period: June to September
• Coverage: Entire Indian subcontinent
• Moisture Source: Arabian Sea and Bay of Bengal branches of the Indian Ocean.
• Significance: Contributes about 75% of India’s total annual rainfall.
• Dominant in: Western Ghats, central India, and the Indo-Gangetic plains.
• Kerala: Receives ~70% of its annual rainfall from SWM.

2. Northeast Monsoon (NEM) – The Retreating Monsoon

• Period: October to December
• Moisture Source: Winds blow from the northeast (land to sea) but gather moisture from the Bay of Bengal, causing rain in southeast India.
• Dominant in: Tamil Nadu, southern Andhra Pradesh, interior Karnataka, and parts of Kerala and Puducherry.
• Tamil Nadu: Receives 48–50% of its annual rainfall from NEM — it’s the state’s main rainy season.

Fact Box:

• IMD data (1901–2020) show the northeast monsoon contributes only 11% to India’s total rainfall, but over 60% for Tamil Nadu and 30% for coastal Andhra Pradesh.

The average onset date over Tamil Nadu is October 20, but in 2025 it began around October 16.

Climate Change and Changing Rainfall Patterns

1. Increased Variability and Intensity

• The India Meteorological Department (IMD) reports that both SWM and NEM rains are now characterised by shorter, high-intensity events, resulting in urban floods and flash runoff.
• According to a Ministry of Earth Sciences (MoES, 2023) report, the frequency of very heavy rainfall events (>115.6 mm/day) has increased by over 12% per decade in peninsular India since 1950.

2. Localised Flooding vs Regional Drought

• While some regions (like coastal Tamil Nadu) receive torrential rains, Rayalaseema and interior Karnataka continue to face deficits, highlighting the spatial inequality of monsoon rainfall.
  

3. Urbanisation Amplifying Floods

• Chennai, Coimbatore, and Madurai face flash floods as urban surfaces are largely impervious due to concrete and asphalt.
• Drainage systems are outdated — for instance, Chennai’s stormwater drainage capacity handles only 12 mm/hour of rainfall, far below the current intensity levels.
  

The Kerala–Tamil Nadu Connection

Mullaperiyar Dam Context

• Built in 1895, located in Idukki district (Kerala) but operated by Tamil Nadu under a 999-year lease to divert water to the Vaigai basin (Theni, Madurai, Dindigul).
• It has a gross storage capacity of 443.23 million cubic metres (MCM).
  

The Current Challenge

• With the early onset of NEM coinciding with residual SWM rains in Kerala, catchment areas in Idukki are overflowing, raising water levels in Mullaperiyar Dam.
• To prevent overtopping, Tamil Nadu has opened all 13 shutters, releasing thousands of cusecs downstream.
• The result is dual flooding — in Idukki (Kerala) and Theni (Tamil Nadu) — as both states face intense rainfall simultaneously.
  

Wider Implication

This overlap demonstrates how inter-state hydrological linkages can transform “excess rainfall” into shared risk, underscoring the need for coordinated reservoir management and real-time data exchange.

Impacts of Excess Rainfall

1. Urban Areas

• Flash floods, sewage overflows, and transport disruption.
• Contaminated water leads to outbreaks of cholera, dengue, and leptospirosis.
• Infrastructure damage due to weakened foundations and high groundwater tables.
  

2. Agriculture

• Waterlogging damages crops, particularly paddy, pulses, and cotton.
• Soil erosion and nutrient loss reduce long-term fertility.
• Fungal infestations like rice blast and sheath blight increase during prolonged wet spells.
• Example: The 2023 Cyclone Michaung floods caused an estimated ₹3,000 crore loss to Tamil Nadu’s agriculture sector.

3. Health and Livelihood

• Stagnant water encourages vector-borne diseases.
• Flood displacement causes psychological distress, especially among rural and coastal communities.
• Economic cost: Chennai floods (2015) cost India nearly $3 billion, highlighting how unplanned urbanisation multiplies risks.

Way Forward

1. Urban Water Resilience

• Implement Integrated Urban Flood Management Plans — combine stormwater drains with green infrastructure.
• Promote permeable pavements, rain gardens, and urban wetlands for natural absorption.
• Enforce zoning regulations to prevent construction on floodplains.
  

2. Agricultural Adaptation

• Encourage flood-tolerant crop varieties (e.g., Swarna Sub-1 rice).
• Invest in micro-irrigation and drainage channels to prevent waterlogging.
• Integrate climate-smart agriculture practices under PM Krishi Sinchayee Yojana (PMKSY).

3. Dam and Reservoir Coordination

• Establish a Kerala–Tamil Nadu Flood Coordination Committee with real-time rainfall and inflow data sharing.
• Upgrade dam automation systems with forecast-based reservoir management.
• Adopt a basin-level approach for rivers like Periyar–Vaigai, transcending state boundaries.

4. Policy and Planning

• Integrate monsoon preparedness into State Disaster Management Plans (SDMPs).
• Mandate Environmental Impact Assessments (EIA) for urban expansion in flood-prone areas.
• Promote community-based flood early warning systems and public awareness campaigns.
  

Conclusion

The early onset of the northeast monsoon is another reminder that India’s monsoon system is no longer predictable or uniform. While rainfall remains essential, climate-induced extremes are transforming abundance into adversity. For Tamil Nadu and southern India, the challenge lies in reframing policy priorities — from rainfall maximisation to risk minimisation.

Excess rain, when unmanaged, erodes both livelihoods and infrastructure. The real resilience lies not in celebrating surplus rainfall but in designing systems that can safely absorb, store, and use it — turning volatility into vitality.

Sample Mains Question

1. The early onset of the northeast monsoon in South India highlights the changing nature of rainfall patterns under climate change. Discuss the implications for agriculture, urban planning, and inter-state water management, suggesting adaptive policy measures.

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