India is experiencing a gradual but widespread decline in sunshine hours across most regions. This trend poses serious challenges for both solar power generation and agricultural productivity, underscoring the urgent need for coordinated climate and pollution mitigation strategies.
Overview Of The Scientific Study
- Study reveals a persistent decline: A study published in Nature’s Scientific Reports in October 2025 found that India’s sunshine duration has consistently decreased over the past three decades.
- Research institutions collaborate on data analysis: The study was jointly undertaken by Banaras Hindu University (BHU), the Indian Institute of Tropical Meteorology (IITM) Pune, and the India Meteorological Department (IMD).
- Long-term data confirms nationwide pattern: Researchers examined sunshine data from 20 meteorological stations spread across nine major climatic regions between 1988 and 2018, confirming a significant nationwide dimming trend.
Regional And Seasonal Variations
- Northern plains face the steepest decline: The North Indian plains recorded the sharpest reduction, losing around 13.1 sunshine hours annually. The Himalayan region followed with a 9.5-hour decline, while the West Coast saw a decrease of 8.6 hours per year.
- Central and southern regions also affected: The East Coast lost 4.9 hours, central inland regions declined by 4.7 hours, and the Deccan plateau by 3.1 hours each year.
- Northeastern India shows relative stability: Unlike other regions, northeastern India displayed only mild seasonal fluctuations and no sustained annual decline. This resilience may stem from its unique climatic system and comparatively lower air pollution.
- Seasonal variations show a distinct pattern: Sunshine hours were higher from October to May but dropped sharply during June and July due to monsoon activity. The Himalayan and northern inland regions exhibited reverse patterns due to altitude and wind circulation differences.
Causes Of Solar Dimming
- Aerosol pollution emerges as the primary cause: Industrial emissions, vehicular exhaust, biomass burning, and fossil fuel use have significantly increased aerosol levels since the 1990s. These fine particles scatter and absorb sunlight before it reaches the surface.
- Cloud cover intensifies the effect: Enhanced cloud formation and persistence have compounded the problem. Studies estimate aerosols reduced sunlight by about 13%, while cloud cover caused an additional 31–44% reduction between 1993 and 2022.
- The Twomey effect explains longer cloud duration: High aerosol concentrations produce numerous small cloud droplets that stay aloft longer and reflect more sunlight. This “Twomey effect” prolongs cloudy conditions and blocks sunlight even without rainfall.
- Stubble burning worsens the northern dimming: Seasonal crop residue burning in Punjab, Haryana, Delhi, and western Uttar Pradesh releases high levels of PM2.5, PM10, and black carbon. These pollutants elevate aerosol density, reducing visibility and sunlight over the Indo-Gangetic Plain.
Implications For Solar Energy
- Dimming threatens India’s solar targets: India aims to achieve 500 GW of non-fossil electricity capacity by 2030, with solar power as a central pillar. However, declining sunshine hours directly impact solar generation efficiency.
- Power generation losses are significant: Research projects that solar output could fall by 600–840 gigawatt-hours annually by mid-century due to pollution and climate change.
- Solar irradiance reduction hampers efficiency: Between 2001 and 2018, India’s usable solar irradiance fell by nearly 30%. Pollution reduces solar panel efficiency by 12–41%, depending on the technology used.
- Economic losses add to the challenge: Reduced solar efficiency translates into annual financial losses estimated between USD 245 million and USD 835 million. Large solar parks in Rajasthan and Gujarat, such as the Bhadla Solar Park, are among the worst affected.
Implications For Agriculture
- Reduced sunlight weakens crop growth: Lower solar radiation affects photosynthesis, leading to slower growth and smaller yields.
- Fungal diseases increase with prolonged moisture: Longer moisture retention on leaves encourages fungal infections and other pest issues, particularly in regions with low sunlight.
- Key agricultural states face higher risk: Punjab, Haryana, and Uttar Pradesh, where agriculture remains the main livelihood, are most affected. Crops like rice, wheat, cotton, and sugarcane—heavily reliant on sunlight—may experience reduced yields and longer growing cycles.
Lessons From International Experience
- China and Japan reversed solar dimming: Both countries successfully reduced aerosol levels after implementing strong air quality policies in the 1990s.
- China’s Clean Air Action Plan improved sunlight: Between 2008 and 2016, China increased its surface solar radiation by roughly 1 watt per square metre per year.
- Japan achieved similar results: Japan’s stringent emission standards also reversed long-term dimming, proving that effective policy can restore solar brightness.
- Global examples show reversibility: These experiences demonstrate that India can reverse its declining sunlight trend through strict emission control, vehicle regulation, and alternatives to stubble burning.
Policy Imperatives And The Way Forward
- Integrated action is essential: Experts urge a comprehensive national response linking air quality management, renewable energy expansion, and sustainable urban planning.
- Strong regulation must accompany clean technology: Industrial and vehicular emissions require stricter enforcement, while technological innovation should enhance solar efficiency under polluted conditions.
- Agricultural solutions can reduce aerosols: Promoting in-situ crop residue management and bioenergy conversion can minimize stubble burning and curb aerosol emissions.
- Innovation complements policy reform: Advances in photovoltaic materials, anti-soiling coatings, and adaptive solar tracking can help maintain performance under low irradiance conditions.
Conclusion
The decline in India’s sunshine hours reflects a broader environmental challenge driven by pollution and atmospheric change. The phenomenon jeopardizes the nation’s solar power expansion and agricultural stability. Yet, lessons from other countries show that with robust emission control and clean energy innovation, the loss of sunlight can be reversed. Safeguarding India’s sunlight is therefore vital for ensuring both energy security and sustainable development.