An estimated 620 million tons of crop residue is generated annually in India, of which 16% is burnt in field. The major contribution in stubble burning is paddy straw (43%), wheat straw (21%) followed by sugarcane (19%). Punjab accounts for 21.32 million tons (mt) stubble burnt every year (out of 51 million tons of crop residue) while Haryana 9.18 mt (out of 28 mt of crop residue).
Over the last 15 years, the total production of wheat and paddy over Punjab and Haryana has increased by 6.96% while the rate of surplus crop residue left over in the field (after utilization for cattle fodder, storage & other uses) is 1.2 mt/yr.
85–90% of the paddy straw is burnt in the field. Surplus rate of crop residue will continue to increase if substantive mechanism for disposal of crop stubble or other alternatives are not provided to farmers as per a study titled ‘Long term influence of groundwater preservation policy on stubble burning and air pollution over North-West India’ in journal Nature.
Wheat stubble is burned in April & May pre-monsoon season and paddy stubble is burned in October & November post-monsoon season in Punjab and Haryana. Satellite data shows that the stubble burning in increasing in recent years. It is estimated that stubble burning fires have increased at a rate of 250 per year over Punjab and Haryana during 2003–2017.
Various studies have proven that stubble burning adversely effects the air quality and thereby human health. Stubble burning has been a major source of seasonal aerosol loading and pollution over northern India.
The economic and health costs of air pollution caused due to stubble burning in North India is around $30 billion per year. The impact of pollution (particularly PM2.5 levels) has increased over North India in the recent times (till 2015) and in post-monsoon in Delhi due to the effect of stubble burning.
On an average around 20% of total PM2.5 concentration observed in Delhi during October and November (post-monsoon) is contributed by external advection and about 50–75% PM2.5 concentration is contributed during the stubble burning period from the upwind region. It is estimated that 66,200 PM2.5 attributable deaths were caused by stubble burning in India in 2015.
Despite the government policies encouraging ways to tackle stubble burning and promote groundwater preservation (Prevention and Control of Pollution Act 1981; The Punjab Preservation of Subsoil Act 2009; The Haryana Preservation of Subsoil Act 2009; National Policy for Management of Crop Residue 2014; National Green Tribunal 2015), the practice is still continuing.
Linkage between groundwater policy and stubble burning
There is good recharge of groundwater in Punjab compared to Haryana and hence, Punjab has comparatively good groundwater condition than Haryana region. The results from GRACE/GLDAS data have shown that Punjab is witnessing low depletion in groundwater storage than Haryana. This ascertains that despite having better groundwater recharge and good amount of rainfall, Punjab is also facing similar chronic water condition like Haryana.
The study investigated the impact of the groundwater act on the changes & pattern in stubble burning, its impact on air pollution in the region and status of groundwater storage thereafter.
The aftereffects of groundwater preservation act i.e., post 2010 era (2011–2020) has seen delay in crop harvesting thereby shifting the peak stubble burning to May (wheat stubble burning) and to November (paddy stubble burning) by 8–10 and 10–12 days compared to pre-2010. Groundwater storage depletion rate of 29.2 mm yr−1 was observed over the region.
Post 2010 era shows an increase of 1.4% in wheat stubble burning and 21% in paddy stubble burning fires over Punjab and Haryana with 70% of PM2.5 air mass clusters (high probability > 0.8) advecting to the downwind regions leading to 23–26% increase in PM2.5 and 4–6% in aerosol loading over National Capital Region (NCR).
The present water preservation act was implemented to preserve the groundwater by delaying the paddy nursery and transplantation. However, this policy has led to delay in harvest & shrinking of harvest window with increased stubble burning fire occurrences (15.8%) and shift in stubble burning by 8–10 days (wheat) and 10–12 days (paddy). The particulate matter pollution associated with stubble burning fires coincides with cultural festivals in India thereby increased pollution over North India.
Although the objective of water conservation policy was supposed to preserve the groundwater by delaying the paddy transplantation and sowing, on the contrary the implementation of this policy has seen groundwater storage after 2013 depleting at a rate of 29.2 mm/yr over these regions.
Post policy implementation has led to shift and shrinking of harvest window with increased occurrences in stubble burning fires which also increase associated particulate matter pollution over North India. This is clear indication that in-spite of the enforcement of the GW act (post-2010 era) there is relatively marginal increase in fire occurrences in pre monsoon stubble burning while substantial jump in post monsoon stubble burning, implying that the stubble burning practice is continuing.
This increase and peak shift of burning pattern (1st week of November) in post monsoon stubble burning season coincide with the festive season in India with high anthropogenic carbonaceous dust, smoke and aerosol particulate matter (PM2.5, PM10) adversely affecting air quality and are advecting to regions of National Capital Region (NCR) and parts of Indo-Gangetic Plain.
The impact on Delhi NCR
The analysis shows that NCR air quality is not only affected from stubble burning but also a combined effect of synoptic low and steady winds, low boundary layer, favorable wind direction and stable atmosphere. In order to improve the air quality over NCR and northern India, long term and short-term steps need to be taken.
Government of India under the National Action Plan for Climate Change (NAPCC) had enforced National Policy for Management of Crop Residue (NPMCR) in 2014. Government is implementing ways to help farmers through use of subsidizing machinery equipment to cut stubble, promote diversified utilization of stubble for in-situ crop management, many industrial application and other uses.
While the positive effect is being visible by way of slight improvement in air quality over NCR but will take time for substantial improvement. Short-term steps include adopting rainwater harvesting & other water conservation technologies for optimal use of available water resources, renovation & use of village ponds, restoring field distributaries & increasing irrigation area under canal system, shifting from monoculture to diversified crop pattern and adopting to replace current rice variety with shorter duration rice varieties. This would shift harvest 10–15 days (in September month) earlier than current practice period.
Almost 21% increase in paddy stubble burning fires over a decade added additional 23–26% of annual PM2.5 concentration over NCR. This high influx of aerosol particulate matter over NCR and downwind regions (particularly during post monsoon stubble burning) is deteriorating air quality in north India to as much of 4–5 times the permissible Indian standard.
However, due to implementation of NPMCR policy & awareness programs among farmers by Government, the stubble burning fires incidents and related pollution over NCR are on marginal decline (5%) over the last 4 years. It is envisaged that the approach and steps proposed in this study could be potential options for policy planners. This in turn will have positive impacts on air pollution with reduced mortality and morbidity rates.
The full paper can be accessed here