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Delays in paddy planting and stubble burning in certain districts of Punjab and Haryana act like a cascade. They have caused excessive pollution in areas downwind over the past decade, a new research paper by Harvard University in the United States has said.
The northern and western districts of Punjab report the maximum delays in planting paddy and the subsequent burning of its stubble. Had these districts not delayed planting paddy, the pollution caused in downwind areas such as the national capital would have been much less.
The delay in rice planting in certain districts of Punjab and Haryana subsequently extends the burning of its stubble, which in turn causes downwind areas to witness heavy pollution year after year.
It was in 2008 that the Punjab and Haryana governments mandated rice planting until closer to the arrival of monsoon rains. ‘Planting’ here means the transplantation of paddy seeddlings that have been grown in a nursery.
The move was made in response to the continuous depletion of groundwater in the two states due to the excessive sowing of paddy.
But the date of planting paddy had not remained static, the research noted.
“Moreover, the earliest paddy sowing date, mandated as June 10 in Punjab in 2008, has not remained static, shifting to June 15 in 2014, June 20 in 2018, and finally to June 13 in 2019,” the paper read.
“Delays in rice sowing shorten the post-monsoon turnaround between monsoon rice harvests and winter wheat sowing, further elevating fire as an attractive option for rice residue management,” it added.
Peak fire activity thus shifted from late October to early November, when cooler temperatures and weak winds trapped haze more, causing excessive pollution.
The researchers collected satellite-based evidence that linked the delays in the rice growing season and post-monsoon fires at the district level in Punjab.
They used a receptor-oriented Lagrangian plume model to simulate the effect of these delays on downwind air quality in six cities.
They found that in the absence of the delay in biomass burning during 2008-2019, cities that are both downwind and near the fire source — New Delhi, Bathinda and Jind — would have consistently recorded 11 per cent-21 per cent less PM2.5 if delays would not have occurred.
For example, in New Delhi, the researchers found that PM2.5 would have on average been reduced by 12 per cent from 2008 to 2019.
“While we show that the delays alone have led to increased PM2.5 in downwind areas, the later fire season also drives further fire activity, thus compounding the net negative impact on PM2.5 exposure,” the researchers wrote.
They suggested that a revised groundwater policy, allowing earlier sowing dates in such districts, could improve air quality in north India while conserving groundwater.
Cascading Delays in the Monsoon Rice Growing Season and Postmonsoon Agricultural Fires Likely Exacerbate Air Pollution in North India was published in the journal Advancing Earth and Space Sciences.
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