Cascading Delays in the Monsoon Rice Growing Season and Postmonsoon Agricultural Fires Likely Exacerbate Air Pollution in North India
Liu, T.; Mickley, L. J.; Patel, P. N.; Gautam, R.; Jain, M.; Singh, S.; Balwinder-Singh, balwinder-singh; DeFries, R. S.; Marlier, M. E.
2022-12-27
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Liu, T.; Mickley, L. J.; Patel, P. N.; Gautam, R.; Jain, M.; Singh, S.Balwinder-Singh, balwinder-singh ; DeFries, R. S.; Marlier, M. E.; (2022). "Cascading Delays in the Monsoon Rice Growing Season and Postmonsoon Agricultural Fires Likely Exacerbate Air Pollution in North India." Journal of Geophysical Research: Atmospheres 127(24): n/a-n/a.
Abstract
Over the past two decades, smoke aerosols from crop residue burning have increasingly degraded postmonsoon (October-November) air quality in north India. We use satellite data and atmospheric modeling to investigate whether cascading delays in monsoon rice growth and postmonsoon fires over 2003–2019 have exacerbated the already poor urban air quality downwind of the fires. Beginning in 2008, a government effort to combat groundwater depletion in Punjab mandated rice sowing until closer to the arrival of monsoon rains. We find evidence of district-level delays in the timing of both monsoon rice growth and postmonsoon fires, which vary from 1 to 4 weeks with largely an east-west gradient. These delays are correlated spatially (r = 0.51–0.77), with northern and western districts in Punjab, which rely less on groundwater for irrigation, tending to have the greatest delays. Had the delays in fire activity not occurred, we estimate that cities downwind and near the fire source would have consistently seen less smoke-related fine particulate matter (PM2.5), on average ranging from 11% to 21% for New Delhi, Bathinda, and Jind during 2008–2019. This net benefit of earlier postmonsoon burning could have been even larger given that (a) a longer rice-to-wheat transition could incentivize farmers to find alternatives to burning crop residues; and (b) background PM2.5 is less abundant earlier in the season, decreasing the likelihood of extreme pollution episodes. Strategies aiming to mitigate air pollution while conserving groundwater may be more effective by promoting an earlier monsoon growing season in districts with less groundwater depletion.Plain Language SummaryDuring the postmonsoon period from October to November, farmers in northwest India have increasingly burned rice residues to quickly clear fields and prepare to plant winter wheat. As seen by satellites, these agricultural fires emit large amounts of smoke that travel to nearby rural areas and populous urban centers, such as New Delhi, contributing to severe air pollution episodes. Beginning in 2008, a government effort to combat groundwater depletion in the state of Punjab mandated rice planting until closer to the arrival of monsoon rains. However, delays in rice planting have led to delays in the timing of postmonsoon agricultural burning. Our modeling results show consistently lower air quality in nearby cities as delayed fires coincide with meteorological conditions that are more favorable for trapping smoke near the surface. Delays in the fire season also shorten the transition period from rice to wheat, thus increasing fire activity further. Strategies aiming to mitigate air pollution in north India may be more effective by stemming the delays in the postmonsoon fire season.Key PointsPunjab, India experienced cascading delays in the monsoon rice growing season and postmonsoon crop residue burning from 2003 to 2019District-level delays vary from 1 to 4 weeks with a longitudinal east-west gradient, where western districts experienced the largest delaysDelays in postmonsoon fires have consistently led to increased air quality degradation across north India from 2008 to 2019Publisher
Wiley Periodicals, Inc.
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2169-897X 2169-8996
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