India has seen a steady decline in sunshine hours over the past three decades (1988-2018), with the north Indian plains and west coast among the hardest hit. The decline is largely attributed to aerosol pollution (from industry, vehicles, biomass burning) and increased cloud cover, which together have dimmed sunlight reaching the ground. Sources: Banaras Hindu University, IITM, India Meteorological Department
Key Findings of the Study
- Data from 20 meteorological stations across nine regions in India show consistent annual declines in sunshine hours for almost all regions, except the northeast, which shows a slight seasonal leveling off.
- North Indian plains: biggest drop — ~13.1 hours/year on average.
- East coast, Deccan plateau, central inland also recorded drops, though smaller (~3-5 hours/year).
- The decline is more pronounced during monsoon months (June-September), when cloud cover and atmospheric moisture combine with pollution to reduce sunlight
Causes
- Aerosols and particulate matter: Tiny particles from vehicle emissions, fossil fuel burning, biomass burning increase in the air. These scatter and absorb sunlight, reducing direct solar radiation.
- Cloud cover and moisture: More persistent clouds, longer lasting cloud droplets (because aerosols often act as nuclei for droplets), and higher humidity help in maintaining overcast conditions.
- Spatial & seasonal factors: Regions with greater industrial activity, urbanisation, or biomass burning show sharper declines. Also, during monsoon season skies stay overcast even without rain, as per observations. The Times of India
Impacts & Implications
- Solar power generation
Reduced sunlight / solar radiation means lower efficiency and output for solar installations. Studies project a drop in solar power potential because of pollution + climate change. - Agriculture & crop yields
Sunlight is critical for plant growth; less sunshine especially during key seasons can affect photosynthesis, crop maturation, and hence yields. - Health effects
Reduced sunlight can potentially lead to vitamin D deficiencies. Also, persistent smog / haze can affect respiratory health. - Climate modelling & planning
Changing solar radiation patterns need to be incorporated into climatological models, forecasts, and energy planning, especially as India pushes for more renewables.
What Could Help Reverse the Trend
- Strict regulation on air pollution — controlling industrial emissions, vehicle exhausts, biomass burning, and dust.
- Improved monitoring of aerosols and cloud cover over time, to understand regional differences and seasonal peaks.
- Investment in cleaner energy & low-pollution practices (electric vehicles, cleaner fuels, better agricultural practices).
- Optimizing solar infrastructure using panels that are more efficient under diffuse radiation, and deploying in regions less impacted by pollution/cloud cover when possible.
Conclusion
The trend of declining sunshine hours across most of India, driven by pollution and cloud cover, is now well-documented. It has real implications for energy, agriculture, health, and climate policy. Addressing the sources of aerosol pollution is essential—not only for cleaner air, but also to preserve sunlight itself, which is a foundational resource for life, energy, and economy.
