Sunshine hours declining due to bad air & thick cloud cover in India, reveals Study

2025 has shown some intriguing climate changes, which can be both worrying and concerning. The monsoon stayed longer than its usual tenure every season, and we couldn't witness the Sun for many days. Moreover, with the La Niña effect, early winters and chilling cold are expected to hit India. With so much happening in the climate, there is data that supports most of it. 

A new study conducted by Benaras Hindu University (BHU), the Indian Institute of Tropical Meteorology (IITM) in Pune, and the Indian Meteorological Department (IMD), among others, has revealed that sunshine hours across many parts of India have been declining over the past 30 years, something that is linked to thickened cloud cover and rising air pollution. 

The study was published in 'Nature's Scientific Reports' in October, examined the sunshine hour data of 20 met stations in nine regions, spanning from 1988 and 2018. Scientists found that the annual sunshine hours, which are the intervals when there is strong sunlight, enough to be recorded as "sunshine hour", have declined in as many as eight regions, except for the Northeast. The north-eastern region showed a marginal seasonal "levelling off."

Here is what the study revealed (according to a TOI report): 

• The sunshine hours on the West Coast fell by 8.6 hours per year, while the North Indian plains recorded an average drop at 13.1 hours an year. 

• Similar declining trends were also recorded in the East Coast and the Deccan Plateau, with 4.9 and 3.1 hours, respectively. The Central India region showed a drop of 4.7 hours per year. 

• The research revealed that sunshine increased during the drier months between October and May, while it swiftly declined in the months of monsoon from June to September. 

• Scientists stated that the long-term 'solar dimming' is associated with higher aerosol concentrations (tiny particles emitted from industries, biomass burning, and vehicles), TOI reported. 

​One of the scientists told TOI, "The released aerosols act as condensation nuclei, creating smaller and longer-lived cloud droplets that keep skies overcast for extended periods. This year's monsoon, too, has been marked by persistently cloudy skies across much of India, especially over the West Coast, Central India, and Deccan Plateau, which saw frequent overcast conditions even on days without rain. Though the study period spans till 2018, trends remain just as relevant today, as the same haze, humidity, and cloud patterns persist - if anything, more strongly than before." 

The declining sunshine hours will majorly affect solar energy generation, agriculture, and climate modelling.