It's All About Timing: Why Study Cited By Centre In Supreme Court Missed The Stubble Burning Around NCR

It’s that time of the year when the Supreme Court of India and government bodies try to dig a well when the house is already set on fire. The annual stubble burning ritual post paddy harvest in Punjab and Haryana is about to conclude and the apex court is castigating the state authorities for their lack of action to control the terrible air quality in Delhi and National Capital Region (NCR).

"We are in the middle of crisis situation? We can't conjure up new solutions", Justice DY Chandrachud commented while hearing a writ petition filed by Aditya Dubey (minor) last year which was first heard on 6 October 2020. As the Solicitor General was taking the bench through the affidavit filed by Centre yesterday regarding the decisions taken to improve the situation, the bench said that the steps being taken were ’long term‘ steps and they wanted to know ‘what are the emergency steps.’

The exchange gives an impression of a court really concerned about the pollution problem in Delhi. But how serious is it?

Let’s understand from the dates the court has heard this matter on. It listed the matter four times in October 2020, once in November and twice in December. In 2021, it listed the matter twice in January, once each in February and March, twice in April and then directly on 28 October, basically when the pollution load had started getting out of control.

The SC didn’t care to take up the matter or follow up on measures taken by the governments for six months.

What’s also interesting to note in the listing of this matter is how the frequency of hearing by the court increases when situation worsens which not so coincidently coincides with stubble burning season in October-November (paddy harvest) and April (wheat harvest).

But the honourable court absolved the farmers of any blame. "Last hearing, we mentioned stubble burning is not major issue, city related issues are there. So if you take steps on them, situation will improve", Chief Justice N.V. Ramana said. Of course, these observations were made even before the Centre submitted its affidavit in the court.

Yesterday, after it made the submission stating that farmers stubble burning contributed to less than 10 per cent of the air pollution in Delhi, Justice Surya Kant observed thus, “Are you agreeing that stubble burning is not the main cause? That hue and cry has no scientific or factual basis?"

“With respect to stubble burning, all affidavits indicate contribution is not much,” the bench said.

Below is the paragraph number 13 from Centre’s affidavit that the court lapped up with such surprise.

The scientific study that this table comes from was published in August 2018 and jointly conducted by The Automative Research Association of India (ARAI) and The Energy and Resources Institute (TERI) for the Department of Heavy Industry, Ministry of Heavy Industries and Public Enterprises.

The Centre made a mistake in relying on this report alone to tone down stubble burning's actual contribution to Delhi-NCR’s pollution. Though, it’s an exhaustive study in terms of different modelling used and locations that were monitored not only in Delhi but in many NCR towns, it has some serious limitations.

First, the report clearly states that “the contribution of agricultural burning is not fully accounted for in this study as the monitoring and modelling periods did not include the month of October, when the burning activities are generally at their maximum. Moreover, the sectoral contributions are averaged for the whole modelling/monitoring period, and hence, do not highlight the contribution of agricultural burning, which happens during a certain number of days and cause episodically high pollutant concentrations.” (emphasis mine)

This frank admission is enough to discard the report from consideration while discussing whether stubble burning is a major factor or not in the pollution load of Delhi-NCR. Not only the Union government but also the Supreme Court didn’t care to enquire basic questions about the limitations of the study, which is the most obvious thing to do when looking at any such scientific report. It conveniently chose to accept the Centre’s submission at the face value.

Second, and this is even more damning limitation, the period monitored per location was only about 10 days. For winter months, it was from fourth week of November 2016 (22nd onwards) to second week of March.

This is how the NASA fire map looked like during the monitoring period in 2016 (22 November to 6 December)

Most of the farm fires are not in Punjab or Haryana but in western Uttar Pradesh which, given the wind flow pattern, won’t have much impact on the air quality of Delhi. No wonder then that agriculture burning didn’t show up as a major factor in TERI-ARAI report.

Below is NASA fire map from 2016 is for period 21 October to 4 November. Had the monitoring period been this, one can easily guess how big a culprit agriculture burning would’ve turned out to be.

Third, the table showing 4 per cent share of agri burning in winters is not the actual average sectoral contribution but obtained only after modelling (dispersion model) where meteorological conditions have also been taken into account. It’s pertinent to note that the conditions vary from year to year and season to season. So, not only the period under monitoring is different in the report, the meteorological conditions were too which can skew the model non-linearly if there is drastic increase in either of the factors - emission from a particular source and the weather conditions (wind pattern, cold).

However, when we look at the annual emission inventory for NCR, the picture becomes slightly clear.

Agriculture burning's share in PM2.5 concentration in NCR is almost 20 per cent annually. Given that stubble burning is an episodic phenomenon observed most fiercely during October-November, it’s not difficult to guess its contribution in pollution load when annually, it’s so high.

Given all this, the Centre should’ve cited various other studies and research on the issue. As per a 2018 paper ‘Agricultural Burning and Air Quality over Northern India: A Synergistic Analysis using NASA’s A-train Satellite Data and Ground Measurements’ published by Dr Hiren Jethva, an Aerosol Remote Sensing Scientist with USRA at NASA Goddard Space Flight Center, ’the mass concentration of PM2.5 escalates from ~50 μg m–3 measured prior to the onset of residue burning in early October to as high as 300 μg m–3 (24-hour averaged, 7- day running mean) during the peak burning period in early November” during 2013-2016, measured in Delhi (emphasis mine).

“A linear regression analysis reveals that the variations in PM2.5 over New Delhi can be attributed to the concurrent changes in the satellite retrievals of fire counts and aerosols over the crop burning area. The back-trajectory analysis shows that most clusters (> 80%) of the northwesterly flow near the ground intercepted the crop burning region before arriving at the receptor location in New Delhi; this further corroborates the transport patterns inferred from the satellite data,” the paper states.

Both the post harvest paddy residue burning as well as the meteorological conditions seem to come into play to make a deadly cocktail for the national capital region.

A study by IIT Kanpur in 2016 could also have been cited by the Central government. Unlike the TERI-ARAI study, the monitoring period of two (Rohini and Okhla) out of six sites in this study starts from the first week of November (3 November) which is usually when the farm fires peak. Therefore, it’s a more dependable source to evaluate the impact of stubble burning in overall pollution. Also, the study like the TERI one uses both dispersion and receptor modelling methods. Using the latter, the study notes:

“The contribution of the biomass burning in winter is quite high at 17% (for PM10) 26% (for PM2.5). Biomass burning is prohibited in Delhi and it is not a common practice at a large scale. The enhanced concentration of PM in October-November is possibly due to the effect of post-monsoon crop residue burning (CRB). It can be seen that the biomass contribution in PM10 in the month of November could be as high as 140 μg/m3 and about 120 μg/m3 for PM2.5 (mean of contribution in entire winter season: 97 μg/m3 and 86 μg/m3 respectively). In all likelihood, the PM from biomass burning is contributed from CRB prevalent in Punjab and Haryana in winter. The back trajectory analyses suggest that the CRB and other biomass emissions may be transported to Delhi from the sources upwind of Delhi (in NW direction). There is an immediate need to control or find alternatives to completely eliminate CRB emissions to observe significant improvement in air quality in Delhi.“ (emphasis mine)

The Parliamentary Standing Committee on Science and Technology, Environment and Forests had presented its report (316th report) on Air Pollution in Delhi and NCR to Rajya Sabha on 7 August 2018 (and tabled in Lok Sabha on the same day). It had also cited the IIT-K study.

This is not to say that the IITK study or the paper by Dr Jethva are without limitations. Certainly not. But in face of uncertainty and inconclusive evidence and especially in the light of serious drawback of the TERI study, it would’ve been appropriate to place all the available estimates before the apex court. Of course, the court itself, if it was serious, should have asked probing questions on the Centre’s submission rather than accepting it so readily.

One hopes that a thorough study is commissioned by the Centre as soon as possible which tracks the sources of emission throughout the year and then act on basis of that evidence. The court would also be better off looking at permanent solutions rather than looking for magic bullets to solve such a grave problem.