New Delhi: As it rained fire in Delhi, large parts of northern and central India remained gripped by a sweltering heatwave on Wednesday, with the national capital experiencing a 79-year high. Delhi's primary weather station, Safdarjung observatory, recorded a maximum of 46.8 degrees Celsius. But, it was the maximum temperature of 52.9 degrees Celsius in Mungeshpur, a densely populated locality amid fields and open spaces on the fringes of the national capital that left weather scientists flummoxed. This prompted the India Meteorological Department (IMD) to examine the automatic weather station in the area for possible sensor errors.

The IMD later clarified that the unusual maximum temperature of over 52.9 degrees Celsius in the national capital's Mungeshpur was due to an "error in sensor or local factor." This statement came after media reports highlighted this figure as the highest ever temperature recorded in the city.

"It looks abnormal and it is an outlier when compared with other weather stations in the national capital region," IMD Director General Mrutyunjay Mohapatra said in a statement.

Examining data and sensors

In an official release, the IMD explained that temperatures across Delhi-NCR varied from 45.2 degrees Celsius to 49.1 degrees Celsius on May 29. However, the reading from Mungeshpur stood out as an outlier compared to other stations. The IMD is currently examining the data and sensors to determine the exact cause of this anomaly. The department suggested that it could be due to a sensor error or an influence of local factors affecting the measurement.

How did the mystery unfold

Hours after the reports of Delhi's Mungeshpur recording a highest temperature of 52.3°C surfaced, Union Minister of Earth Sciences Kiren Rijiju raised a question about this and said that the drastic rise in temperature is 'unlikely'. Taking to X, the minister wrote, "It is not official yet. Temperature of 52.3°C in Delhi is very unlikely. Our senior officials in IMD have been asked to verify the news report. The official position will be stated soon."

Later, the Union Minister also shared the official statement issued by the India Meteorological Department. The weather department clarified that there was an error in the sensor or a local factor. It further added that the temperature variation was likely due to due to “local exposure factors such as proximity to water bodies, barren land, concrete and dense urban clusters, green areas.”

The IMD also stated that it is investigating the sensor error or local factor that caused the anomalous temperature reading in Mungeshpur. The department's clarification aimed at addressing public concerns and to ensure the accuracy of future weather data.

IMD Full Statement on Error in the Sensor

Since the summer of 2022, the India Meteorological Department (IMD) has installed an Automatic Weather Stations (AWS) network and initiated operational reporting of temperature and rainfall observations for 15 new locations spread across different parts of Delhi and the NCR, in addition to manual departmental stations.

The maximum temperature recorded on May 29, 2024, by five departmental observatories (Safdarjung, Palam, Ayanagar, Ridge, and Lodi Road) and 15 AWS are given in Table 1. The maximum temperature over Delhi NCR varied from 45.2°C to 49.1°C in different parts of the city. Mungeshpur reported 52.9°C as an outlier compared to other stations. This could be due to an error in the sensor or a local factor. The IMD is examining the data and sensors.

The maximum temperature on May 29, 2024, has fallen at many places in Delhi compared to yesterday (refer to Table 1). It rained in many places in Delhi in the afternoon, resulting in a further fall in temperature. Heatwave conditions will reduce over the next 2–3 days due to a gradual fall in temperature associated with an approaching western disturbance, rainfall/thunderstorm, and southwesterly wind blowing from the Arabian Sea to northwest India.

Temperature over urban areas varies from place to place due to local exposure factors such as proximity to water bodies, barren land, concrete and dense urban clusters, green areas, etc. The IMD has five major stations regularly reporting observations over a long period, referred to as climate stations. Long-period data fulfilling all the exposure conditions are available from these five departmental observatories of the IMD, as shown in Table 1. Data from these five stations should be considered to find trends and extremes.

Heat wave conditions likely to abate

The IMD has forecasted a reduction in heatwave conditions over the next 2-3 days. The weather office has said that the heat wave conditions were likely to abate over the next couple of days due to a western disturbance, rainfall, thunderstorms and moist south-westerly winds blowing from the Arabian Sea to northwest India.

This shift has already begun, with parts of Delhi-NCR experiencing light showers on Wednesday afternoon, leading to a fall in temperatures.