WASHINGTON — Farmers across northern India are increasingly burning crop residue later in the day, a shift that scientists say is making it harder to monitor stubble burning and accurately assess its impact on air quality, according to new satellite observations cited by NASA.
For decades, seasonal crop fires have blanketed the Indo-Gangetic Plain with smoke and haze from October through December as farmers clear rice residue after harvest. While the overall stubble-burning season in 2025 largely followed historical patterns, the daily timing of fires has shifted noticeably in recent years, NASA said in a statement released Monday.
“In many ways, the seasonal pattern looked familiar,” said Hiren Jethva, an atmospheric scientist at Morgan State University based at NASA’s Goddard Space Flight Center. “Air quality deteriorated in Delhi and several other cities for about a month after fires intensified in the last week of October.”
What has changed, Jethva said, is when the fires are being set. For years, most stubble burning occurred in the early afternoon, typically between 1 p.m. and 2 p.m. local time. New analysis shows that fires are now more likely to occur between 4 p.m. and 6 p.m.
“Farmers have changed their behavior,” Jethva said.
The shift was identified using data from South Korea’s GEO-KOMPSAT-2A geostationary satellite, which has collected observations every 10 minutes since its launch in late 2018. By contrast, commonly used fire-monitoring instruments such as MODIS and VIIRS pass over the same location only once or twice a day, increasing the risk that later-day fires go undetected.
Satellite imagery highlights the scale of the issue. On November 11, 2025, NASA’s Aqua satellite captured a dense plume of smoke spreading across Punjab, Haryana, Uttar Pradesh, and Madhya Pradesh. News reports said it was the first of several days that year when India’s air quality index exceeded 400, the highest level on the scale.
As in previous years, severe pollution led authorities in some regions to close schools and tighten restrictions on construction and other activities. Scientists say stagnant winds and unfavorable atmospheric conditions can push pollution levels several times above World Health Organization guidelines during peak burning periods.
Jethva’s analysis found that stubble burning in Punjab and Haryana in 2025 was moderate compared with other recent years. Fire counts were higher than in 2024, 2020, and 2019, but lower than levels recorded in 2023, 2022, and 2021.
Indian researchers have independently reported similar findings. A 2025 study published in Current Science showed peak fire activity shifting from about 1:30 p.m. in 2020 to roughly 5 p.m. in 2024, based on Meteosat Second Generation satellite data. In December 2025, researchers at the International Forum for Environment, Sustainability, & Technology released a multi-satellite analysis reaching comparable conclusions.
While the role of stubble burning in Delhi’s air pollution is widely acknowledged, scientists continue to debate how much it contributes compared with other sources such as vehicles, industry, domestic cooking and heating, fireworks, and dust storms.
“Studies report contributions ranging from 10 to 50 percent,” said Pawan Gupta, a NASA research scientist specializing in air quality.
Gupta estimates that crop burning accounts for 40 to 70 percent of pollution on peak days, falling to 20 to 30 percent when averaged over a month and less than 10 percent on an annual basis. He noted that meteorological factors — including low temperatures and a shallow boundary layer during the burning season — further complicate pollution modeling.
Scientists warn that later-day fires may worsen overnight pollution buildup, as evening burns often coincide with weaker winds and atmospheric conditions that trap pollutants closer to the ground. (Source: IANS)
