The unprecedented temperature of 52.9° Celsius reported in Delhi on May 29 is likely to have been due to a reading from a faulty instrument, and not a weather phenomenon. The India Meteorological Department (IMD) is conducting an investigation into the matter, The Hindu has learnt from conversations with multiple senior officials in the department.
With Delhi and several parts of north India reeling under an intense heatwave, Wednesday’s reading suggested that Delhi had broken a temperature ceiling that hadn’t even been breached in western Rajasthan, which is usually a region of recording-breaking temperatures in India.
The reading reported out of a single station in Delhi’s Mungeshpur was a large three degree rise from that of the previous day’s (May 28) reading at the station of 49.9° Celsius. Except for the weather station at another location, Narela, which reported a 1.5° C jump over the previous day, all other stations reported less than a degree of deviation.
The weather station at Mungeshpur is an automatic weather station (AWS), one of 16 such stations deployed by the agency to measure variations in temperature, humidity, and rainfall across Delhi. Deployed only since 2022, they work differently from the IMD’s five “departmental” or manually-operated weather stations that have been the official source of Delhi’s weather since decades. The manual weather stations have people reading a traditional thermometer to measure and report temperatures four times a day. The AWS, on the other hand, relies on sensors (thermistors) and generates meteorological values on demand, and the information is made available on the agency’s website on an hourly basis.
While the AWS’ are a vital cog in the modern meteorological observation network, and are extremely accurate, durable and consistent, experts say that the IMD doesn’t yet have all-round expertise on these instruments.
“It was clear that this was an outlier. If at least one or two of the 21 weather stations had reported a temperature of at least 50° [Celsius], then such a reading of 52.9° would still be considered plausible,” a senior meteorologist from the organisation told The Hindu. “While manual observations and thermometers are well understood, AWS are more complex instruments. While very accurate, they may, like any other instrument, be prone to error and go undetected for a while. This is a learning experience for us.”
A “thorough test and investigation is underway” before a final conclusion can be drawn on the Mungeshpur reading, M. Mohapatra, Director-General, IMD, told The Hindu. If the instrument at Mungeshpur was faulty, there was no indication over previous days that its readings were off, the official said.
Once the Mungeshpur reading became public, the IMD had an expert investigate it. However, in its public statement on Wednesday evening, the agency wasn’t categorical on whether the reading was erroneous.
“The maximum temperature over Delhi NCR varied from 45.2° to 49.1° C in different parts of city. Mungeshpur reported 52.9° C as an outlier compared to other stations. It could be due to error in the sensor or the local factor. IMD is examining the data and sensors,” the weather body’s statement on Wednesday noted.
The statement also recommended that temperature extremes be reported by relying on figures from the IMD’s departmental or manually-run weather stations. Earth Sciences Minister, Kiren Rijiju, under whom the IMD falls, had also posted on social media platform X regarding the readings.
Another scientist associated with the IMD said that the accompanying rains reported in some places in Delhi, as part of a western disturbance, had cooled temperatures, and so, a 52.9° C reading was highly unlikely. “AWS, while necessary and useful, also requires frequent calibration and checking. We don’t yet know what the specific circumstances are that surrounded the Mungeshpur reading,” the scientist added.
