In recent times, crop residue burning in India’s northern states, specifically Punjab and Haryana, has been under scrutiny for its contribution to the worsening air quality in the national capital, Delhi. A new study further examines this issue, shedding light on how meteorological conditions and the timing of stubble burning play significant roles in Delhi’s pollution crisis.
The Practice of Crop Burning
A common method used by farmers in Punjab and Haryana to prepare their fields for winter sowing is crop burning. This process typically begins in October and peaks in November, aligning with the withdrawal of the southwest monsoon. The pollutants and particulate matter (PM) from the burnt crop residue, combined with other pollution sources in Delhi, get trapped in the lower atmosphere. This significantly exacerbates the city’s winter pollution.
Increased subsidies and assured procurement of rice have led to a surge in rice cultivation. Modern farming techniques which extract only the rice grains have inadvertently escalated this issue by leaving behind large quantities of rice stubble.
Legislation and Its Impact
The Punjab Preservation of Subsoil Water Act 2009 was enacted to discourage excessive groundwater extraction. It made it mandatory for farmers to delay rice sowing until late June. This has resulted in an average delay of 10 days compared to 2002-2008. Consequently, the burning of rice crop residues now perfectly coincides with the withdrawal of the southwest monsoon.
Results of the Study
According to the study, crop burning contributed nearly 40% of the near-surface PM2.5 in Delhi in 2016, leading to one of the city’s most severe pollution episodes. The research heavily relied on mathematical modelling, using data on the number of crop burning incidents and PM levels.
The findings revealed that the contribution of crop residue to PM over Delhi in 2016 increased marginally (by 1%) when compared to a hypothetical scenario where crops were burned 10 days earlier. While early burning decreased PM levels by 20g/m3, it did not reduce the number of days of significant PM exposure in Delhi, which remained around 55 days.
Interestingly, the study also pointed out that delaying rice stubble burning by 10 days from the current practice could be more harmful. It would lead to an increase in peak PM emissions and prolong the number of pollution days.
Way Forward
Ceasing crop residue burning can significantly contribute to achieving the goals of the National Clean Air Programme (NCAP). The NCAP aims to reduce pollution by 20-30% in annual PM concentration by 2024.
Implementing a mix of incentives and prosecution could be another effective method. Authorities could incentivise farmers adopting eco-friendly methods and penalise those who don’t.
While the impact of legislation may seem negligible, it plays a crucial role in improving or worsening air quality, depending on the prevailing meteorological conditions. Thus, amendments to existing laws, considering these aspects and findings, can significantly help alleviate the issue of air pollution.
