India’s Declining Sunshine Hours

A study published in Nature’s Scientific Reports (2025), reveals that sunshine hours across most of India have declined steadily from 1988–2018, due to increased cloud cover and aerosol pollution.

• The Study was conducted jointly by Banaras Hindu University (BHU), Indian Institute of Tropical Meteorology (IITM Pune), and India Meteorological Department (IMD).

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Key Findings of the Study

• Declining Sunshine: Sunshine hours, the duration when sunlight is strong enough to be recorded have fallen across almost all Indian regions over the past three decades.
• Regional Decline Rates:
• • North Indian Plains: Steepest fall of 13.1 hours per year.
  • West Coast: Decline of 8.6 hours per year.
  • East Coast: Decline of 4.9 hours per year.
  • Central Region: Decline of 4.7 hours per year.
  • Deccan Plateau: Decline of 3.1 hours per year.
  • Northeast India: marginal stabilisation observed
• Seasonal Variation: 
  • Sunshine increased between October and May (dry months).
  • Sharp declines between June and September (monsoon months), coinciding with heavier cloud cover and persistent haze.

Causes of ‘Solar Dimming’

• Aerosol Pollution:
  • Rising industrial emissions, biomass burning, and vehicular exhaust increase aerosol concentration.
  • Aerosols act as condensation nuclei, forming smaller, longer-lived clouds that extend overcast conditions.
• Persistent Cloud Cover:
  • Aerosols prolong cloud lifespan, increasing cloud residence time and reducing solar radiation reaching the ground.
  • The 2025 monsoon season reflected this pattern, with frequent overcast skies even without rainfall, especially across the West Coast, Deccan, and Central India.
• Climate Feedback Loop:
  • Reduced solar radiation alters land–atmosphere heat exchange, potentially influencing monsoon circulation and rainfall variability.

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Implications for India

• Renewable Energy: The decline in solar radiation poses a challenge to solar power generation, potentially affecting India’s renewable energy targets under the National Solar Mission.
• Agriculture: Lower sunlight affects photosynthesis and crop productivity, especially for solar-sensitive crops like paddy and wheat.
• Climate Modelling: Solar dimming alters the energy balance, impacting regional monsoon dynamics and long-term climate forecasts.

Public Health: Reduced ultraviolet radiation could influence vitamin D synthesis, while high aerosol concentration worsens air quality and respiratory health.

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