A measure to conserve groundwater in northwestern India is causing added air pollution in the region already beset by haze and smog, according to a study that used time-series satellite data from NASA.
The study, published in the journal Nature Sustainability, reveals how water-use policies require farmers to transplant rice later in the year, which in turn delays harvests and concentrates agricultural burnings of crop residues in November, a month when breezes stagnate, leading to increased air pollution.
Researchers at the Cornell University in the US noted that the perfect storm of conditions during November has created almost 30 per cent higher atmospheric concentrations of fine particulate matter, small particles that are especially concerning for human health.
Scientists, including those from the International Maize and Wheat Improvement Center (CIMMYT), analysed groundwater conservation policies and their effect on the timing of farmers' planting and harvesting crops and burning crop residues.
They also connected this information with meteorological and air pollution data.
"This analysis shows that we need to think about sustainable agriculture from a systems perspective, because it's not a single objective we're managing for -- it's multidimensional, and solving one problem in isolation can exacerbate others," said Andrew McDonald, associate professor at Cornell.
Northwest India suffers from two critical sustainability issues: air pollution and groundwater depletion.
Almost 1.1 million Indians died from air pollution in 2015, adding up to costs equalling three per cent of the country's gross domestic product, according to the study.
Groundwater depletion is an ongoing issue, and rice cultivation is particularly water-intensive, said researchers, including Balwinder-Singh, a cropping systems simulation modeler at CIMMYT in New Delhi.
In northwest India, two groundwater conservation measures enacted in 2009 delayed groundwater use by farmers until later in the season, researchers said.
The acts ultimately prohibited transplanting rice into paddies until after June 20, they said.
Using time-series satellite data from NASA, the researchers showed that for six rice seasons before the groundwater acts were implemented, an average of 86 per cent of the rice-growing area in the states of Punjab and Haryana was planted on or before June 28.
Less than 40 per cent was planted on or before that date after the acts passed, according to the study.
Data showed that rice harvests then shifted later, with an aggregate eight-day harvest delay in late October and early November, researchers said.
This shift has led to a narrower window and a significant increase in crop residue burning in the first three weeks of November, they said.
Before the acts, the peak date for agricultural fires was October 24, with 490 fires per day; it was November 4, with 681 fires per day, after the acts were passed.
At the same time, meteorological data revealed that the first two weeks of November were on average cooler than the last two weeks of October, coupled with weaker winds, causing increased, stagnating air pollution in New Delhi, which is heavily affected by particulate matter from these agricultural fires.
Farmers must quickly clear residues immediately following rice harvests in this area, known as India's bread basket, to prepare fields for planting wheat that grows in the winter, researchers said.
Solutions could include new agronomic technologies such as the tractor-mounted Happy Seeder, a device that allows farmers to drill through heavy crop residues and plant seeds without burning, they said.
They might couple such advances with shorter-duration rice varieties that offer flexibility in planting and harvesting dates.
Other options include investigating alternative uses for crop residues, such as collecting and selling biomass for power generation, bio-char creation, or as material for paper or furniture.
"There may be uses that are economically viable but they have to be considered as part of a comprehensive solution," McDonald said.
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