NEW DELHI: The number of hours Delhi recorded severe air quality has tripled since 2010, according to a new study. This rise is largely linked to a shift in stubble burning timing caused by the 2009 Groundwater Conservation Policy implemented in Punjab and Haryana.
The policy delayed paddy sowing, shortening the harvest and planting cycle. As a result, farmers now burn crop residue in early to mid-November instead of late October. The timing shift increased the daily 4 pm Air Quality Index by around 90 points and raised “severe” pollution hours by 275%, from 89 hours to 334 hours.
Researchers said the new burning window coincides with cooler temperatures, weaker winds, and lower boundary layer conditions, which trap smoke near the surface. This has led to a sharp rise in daily average PM 2.5 levels.
The study, titled “The role of atmospheric feedback and groundwater conservation policies in degrading air quality in Delhi”, was conducted by the Indian Institute of Tropical Meteorology, the National Centre for Atmospheric Research (USA), and the Commission for Air Quality Management. Researchers used high-resolution atmospheric models and data from 2017–2021, comparing post-policy fires in early-mid November with pre-2010 fires occurring 15 days earlier.
Delhi-based environmentalist Bhavreen Kandhari said, “By shifting burning into a period with lower wind speeds and a shallower boundary layer, smoke accumulation intensified, worsening PM 2.5 levels. Policymakers must balance groundwater conservation with protecting air quality.”
The study also highlighted that smoke transport from Punjab and Haryana, carried by northwesterly winds, continues to be a major contributor to Delhi’s winter pollution, underscoring the need for targeted residue management strategies.