India experiencing steady decline in sunshine hours: Study

A new study has revealed a consistent decline in sunshine hours (SSH) across most regions of India between 1988 and 2018, with the sharpest fall recorded in northern inland areas and the Himalayan region.

The research, published in Scientific Reports and titled ‘Spatiotemporal trends in sunshine hours over India during three decades from 1988 to 2018’, links the trend to rising aerosol concentrations, urbanisation, and changing atmospheric conditions that reduce solar radiation reaching the Earth’s surface.

The study, based on data from 20 weather stations across the country, found that SSH declined at an average rate of 4.88 hours per year along the east coast, 8.62 hours per year on the west coast, and 13.15 hours per year in northern India. The Himalayan region recorded a dimming rate of 9.47 hours annually, while island locations in the Arabian Sea and Bay of Bengal also saw decreases of 5.72 and 6.10 hours per year, respectively.

Researchers said the dimming trend reflects a complex interplay between aerosols (suspended solid and liquid particles in air), cloud cover, and regional meteorology. Increased emissions from fossil fuel consumption, biomass burning, and industrial activities during the 1990s have contributed to higher aerosol concentrations in the atmosphere, reducing transmissivity and sunlight penetration.

The report noted that sunshine duration depends heavily on concurrent weather, with clouds, fog, and dust storms acting as major barriers to solar incidence. Hygroscopic aerosols—acting as cloud condensation nuclei—alter cloud droplet size and lifetime, extending the cloud’s residence time and further limiting solar radiation. This “aerosol indirect effect” has prolonged cloudy conditions, particularly in industrial and coastal belts.

Seasonal analysis showed that SSH peaks during the pre-monsoon months (March–May) and drops significantly through the monsoon period (June–September). The northeast region, influenced by high humidity and dense vegetation, showed the smallest decline, with some positive anomalies during monsoon and post-monsoon seasons.

The east coast cities—Chennai, Machilipatnam, and Bhubaneswar—recorded annual averages of 2244±84 hours of sunshine, but with a downward trend. The brightest year was 2004, while 2010 marked the darkest, according to the dataset.

Experts said the findings have serious implications for India’s solar energy potential, as reduced SSH directly affects energy generation efficiency. “Understanding these variations is crucial for solar energy developers and planners,” the study noted, adding that the data can help prioritise regions for solar panel installations and inform future renewable energy strategies.

The researchers called for further analysis of seasonal cloud patterns and aerosol impacts, highlighting the need to integrate atmospheric insights into renewable energy planning. Despite India’s large solar capacity push, they warned that persistent dimming and reduced sunshine hours could challenge future solar generation targets unless air quality and land-use policies are aligned with energy goals.