Hours of sunshine received in most of India declined every year during 1988-2018: Study

Most of India could be receiving fewer hours of sunshine in a year, with the Himalayan region and west coast seeing the highest reductions, according to an analysis of trends during 1988-2018.

Researchers from the Banaras Hindu University, Indian Institute of Tropical Meteorology and India Meteorological Department found that on average, sunshine received by the Himalayan region fell by about 9.5 hours every year during the study period, while that in the west coast fell by over 8.5 hours every year.

The analysis, published in the journal Scientific Reports, looked at data collected from over 20 stations in nine geographically diverse regions across India.

Areas in the Deccan Plateau were found to receive three hours fewer sunshine every years over the three decades, while sunshine received in the north eastern region declined at about 1.5 hours every year.

The authors wrote, "The trend analysis depicted annual negative trend in all geographical regions with different rate (west coast: minus 8.62 hours/year; Deccan plateau: minus 3.05 h/year; north eastern region: minus 1.33 h/year; Himalayan region: minus 9.47 h/year)."

Sunshine hours in a month increased during October to May, followed by significant reductions during June-July in six regions, except northern inland and Himalayan region that showed comparatively opposite monthly trends, the team said.

"The study reveals persistent decline of (sunshine hours) in Indian subcontinent on all temporal scales excluding north eastern region where mild seasonal levelling off was found," the authors wrote.

Studies have shown that India has experienced persistent solar dimming — receiving lesser sunshine over time — in the 21st century, with increase in density of aerosol particles in the earth's atmosphere being the most accepted reason.

An increase in urbanisation, industrialisation and land-use changes during the 1990s period of India's economic growth — led to burning of fossil fuels, vehicle emissions and biomass — significantly raising aerosol levels in the air and reducing solar radiation, the authors said.

However, hours of sunshine received remain under-researched, especially in India, even though a decline in sunshine received may stand to impact the country's solar energy strategy, they said.