A measure to conserve groundwater in northwestern India has led to unexpected consequences: added air pollution in an area already beset by haze and smog.

A new study 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.

The perfect storm of conditions during November has created almost 30 percent higher atmospheric concentrations of fine particulate matter, small particles that are especially concerning for human health.

The study, "Tradeoffs Between Groundwater Conservation and Air Pollution From Agricultural Fires in Northwest India," published in Nature Sustainability, is a collaboration between researchers from Cornell and the International Maize and Wheat Improvement Center (CIMMYT).

The scientists analyzed 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 of soil and crop sciences and a co-author of the paper. Balwinder Singh, a cropping systems simulation modeler at CIMMYT in New Delhi, India, is the paper's first author.

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 equaling 3 percent of the country's gross domestic product, according to the study.

Groundwater depletion is an ongoing issue, and rice cultivation is particularly water-intensive. News reports in June shed light on water scarcity in Chennai, in the south; in the northwest, two groundwater conservation measures enacted in 2009 delayed groundwater use by farmers until later in the season. The acts ultimately prohibited transplanting rice into paddies until after June 20.

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.

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 might couple such advances with shorter-duration rice varieties that offer flexibility in planting and harvesting dates.