With air quality in Delhi plummeting to hazardous levels, despite a five-year decline in the instances of stubble burning in Punjab, experts suggest that the current approach to satellite based tracking of farm fires by government agencies may be leading to under-reporting the number of fires.
Hiren Jethva, a researcher who studies air flow in particulate matter and the role of farm fires at the Morgan State University in the U.S., has been saying in a series of posts on X since mid-October that the drop in instances of fires from Punjab may be an illusion.
The data on fire counts are from a heat-sensing instrument on two American satellites — Suomi-NPP and NOAA-20 polar-orbiting satellites. Instruments on polar-orbiting satellites typically observe a wildfire at a given location a few times a day as they orbit earth, pole to pole. They pass over India from 1 p.m. to 2 p.m. The instrument on them, called the Visible Infrared Imaging Radiometer Suite (VIIRS), can sense aerosols, smoke, heat and is considered the most accurate to track wildfires across the globe. While the satellites map any particular location twice in 24 hours, they can miss fires that are set and extinguished outside the period of tracking.
Mr. Jethva said that data from another satellite, the GEO-KOMSAT 2A, a Korean satellite that, unlike the polar satellites, tracked the same swathe of earth continuously, seemed to suggest that there was a spike in smoke and fires in the late afternoon in the Punjab province in Pakistan and Punjab in India.
Moreover, the quantity of aerosols, or airborne pollutants, in the atmosphere had not shown any measurable change despite a decline in fire counts, he posted.
As of November 17, there have been 42,314 fires reported since September 15. This is the lowest since such data was made publicly available in 2012. In 2016, 1,33,442 fires were reported during a comparable period — an all-time high, according to bulletins by the Indian Agricultural Research Institute.
Last year, 65,600 fires were recorded — about half of them from Punjab alone. The State, being India’s highest paddy cultivator, has been responsible for 50-60% of farm fires in most years. This year, however, Punjab reported only 8,404 fires as of November 17, or a fifth of the total. Haryana too has reported a record low of only 1,000 fires.
Other researchers also suggest that merely relying on fire counts from the polar satellites may be inadequate and newer satellite data parameters, such as estimating the actual extent of fields burned, may be a more accurate indicator of the true measure of stubble burning.
Professor Sachidanand Tripathi of IIT-Kanpur said that eastern Pakistan has reported a massive spike in air pollution in the past 10 days and therefore would have ferried great quantities of pollutants across the border.